The Limbs

Contrast Medium ●● the role of intravenous gadolinium chelate: routine post-contrast T1W SE images are generally not of

additional value in the assessment of musculoskeletal tumours: ●● contrast enhancement is advised in the assessment of suspected bone/joint/soft-tissue infection, and for the

differentiation of cystic from solid lesions ●● dynamic contrast-enhanced MRI:5 may be of value in differentiating peritumoural oedema and soft-tissue

tumour infiltration, the latter enhancing more rapidly: ●● quantitative dynamic contrast-enhanced MRI shows promise in determining the degree of

chemotherapy-related necrosis in Ewing sarcoma and osteosarcoma, correlating fairly well with histopathological findings6

●● it may also be of value in discriminating between local recurrence and post-operative granulation/scar tissue ●● recent studies have suggested that static and dynamic contrast-enhanced MRI can aid the differentiation

of benign and malignant soft-tissue tumours

Additional Techniques ●● MR angiography without contrast enhancement:7 a technique of fresh blood imaging (FBI) has been used to

assess the vascularity of bone and soft-tissue tumours, and relationship to major neurovascular structures ●● in vivo 1H MR spectroscopy:8 identification of a discrete choline peak has been shown to have a sensitivity

of 88% and specificity of 68% in the detection of musculoskeletal tumours, and can evaluate response to treatment and identify recurrent tumour: ●● however, overlap of imaging findings with some benign tumours, including giant cell tumour (GCT) may

limit the overall utility of this technique

●● diffusion-weighted imaging (DWI):9 multi-shot spin echo echo-planar (SE-EPI) DWI has been used to differentiate between benign and malignant soft-tissue masses: ●● the apparent diffusion coefficient (ADC) values for benign and malignant tumours overlap, and therefore

do not allow adequate differentiation10 ●● however, the ADC values for tumours increases following chemotherapy and radiotherapy, and may prove

of value in assessing treatment response, although care must be taken to avoid diagnostic pitfalls due to unrelated confounding factors that influence the ADC11

●● T1W SE images are sensitive to fatty atrophy and acute haemorrhage, while STIR/FS T2W FSE images are sensitive to muscle oedema

●● muscles are best imaged in the axial plane, allowing optimal assessment of which muscle group is involved, while sagittal/coronal images give the best assessment of the longitudinal extent of muscle abnormality

●● administration of intravenous gadolinium: ● may optimise the diagnosis of subtle muscle trauma that is occult on T2W/STIR images ● may allow optimal demonstration of torn muscle fibres in the presence of excessive haemorrhage and

oedema ●● pre-and post-exercise imaging may be of value in exertional compartment syndrome:

● acute increase in T2W muscle SI is termed ‘exercise enhancement’ and is thought to be due to increased extracellular water, occurring within 30 minutes of exercise

●● imaging during muscle contraction may demonstrate muscle hernias and muscle retraction ●● advanced imaging techniques: including diffusion tensor imaging (DTI), fibre tracking, blood-oxygen-

level dependent (BOLD) imaging, dynamic contrast-enhanced MRI and 1H-MR spectroscopy, are used to evaluate muscle fibre architecture, structure, contractility, microvasculature and metabolism

●● multi-nuclear imaging using phosphorus and sodium shows potential in the imaging of skeletal muscle disorders, including myotonic dystrophy13

●● utilises a FS T2W FSE sequence to limit the signal from skeletal muscle, perineural fat and intraneural fat, leaving the resulting signal from the endoneurial fluid content

●● high SI from vessels must also be suppressed ●● MR neurography: may be subject to magic angle artefact as with tendons and ligaments, resulting in

increased nerve SI when the imaged nerve is orientated at 55° to the main magnetic field: ● in contrast to tendons, peripheral nerves are susceptible to magic angle artefact at longer TEs

●● DTI: measures the molecular motion of water to provide information about the orientation and architectural organisation of the tissue, and tractography allows 3D visualisation of fibre tracts:

● by means of ADC, fractional anisotropy values and nerve fibre orientation, these techniques are of use in imaging of compression neuropathy and traumatic nerve damage

The Arm The Bones ●● the humerus: extends from the glenoid cavity at the glenohumeral joint, to the elbow ●● specific bony landmarks:

●● the deltoid tuberosity is located approximately half way down the lateral aspect of the humeral shaft (Fig. 8.1a)

●● behind and below the deltoid tuberosity is the spiral groove, within which runs the radial nerve (Fig. 8.1b) ●● the distal shaft expands to form the medial and lateral supracondylar ridges (Figs 8.1c, d), which continue

to the medial and lateral epicondyles

●● the arm: is divided into anterior and posterior compartments, which are enclosed within the deep fascia ●● the anterior and posterior compartments are separated by medial and lateral fascial septa (Fig. 8.2a), which

extend from the deep fascia to the medial and lateral supracondylar ridges of the humerus ●● the anterior compartment: contains the biceps brachii, coracobrachialis and brachialis muscles, all of which are

innervated by the musculocutaneous nerve, which is located between the biceps brachii and brachialis muscles ●● biceps brachii: lies within the anterior aspect of the arm (Fig. 8.2b):

●● it arises from 2 attachments (long head-supraglenoid tubercle, short head-coracoid process), the 2 tendons of which combine in the mid-upper arm and insert into the posterior aspect of the proximal radius, crossing 2 joints

●● one or more additional heads may be present, most commonly arising from the humerus at the site of insertion of coracobrachialis, and seen in up to 20% of the population16-18

●● a variant with persistence of the 2 separate muscle bellies and 2 discrete distal tendons inserting onto the proximal radius has been described19,20

●● a fibrous band known as the lacertus fibrosus arises from the distal bicipital musculotendinous junction and fuses with the forearm fascia21

●● the distal biceps tendon lacks a tendon sheath, but is separated from the anterior radial cortex by the bicipitoradial bursa, which is usually only visible when distended

●● coracobrachialis (Figs 8.2c, d): arises from the tip of the coracoid process and inserts into the middle of the medial side of the humeral shaft

●● brachialis: arises from the anterior surface of the lower half of the humerus (Fig. 8.2e) and inserts into the coronoid process of the ulna, crossing the elbow joint and lying deep within the compartment, immediately anterior to the distal humerus

●● the posterior compartment: contains the triceps muscle, which is innervated by the radial nerve: ●● the long head of triceps arises from the infraglenoid tubercle ●● the lateral head arises from the upper half of the posterior humeral shaft above the spiral groove (Fig. 8.3a) ●● the medial head arises from the lower half of the posterior humeral shaft below the spiral groove, and is

located deep to the lateral and long heads (Fig. 8.3b) ●● the common tendon inserts into the olecranon process of the ulna

●● the deltoid muscle: is located in the lateral upper arm, is innervated by the axillary nerve and functions to abduct the arm: ●● it comprises anterior, middle and posterior bellies (Fig. 8.4), which converge to insert into the deltoid

tuberosity (Figs 8.1a, b)

The Nerves and Vessels ●● the brachial artery: begins at the lower border of the teres major muscle as a continuation of the axillary

artery, and runs in the medial aspect of the arm between the anterior and posterior compartments (Fig. 8.5a), terminating opposite the neck of the radius by dividing into the radial and ulnar arteries

●● the median nerve: is a continuation of the medial and lateral cords of the brachial plexus, running lateral to the brachial artery in the upper arm but medial to the artery in the lower arm (Fig. 8.5b)

●● the ulnar nerve: originates from the medial cord of the brachial plexus and runs posteromedial to the brachial artery in the upper arm (Fig. 8.5a): ●● in the mid-arm, the ulnar nerve pierces the medial intermuscular septum to enter the posterior

compartment (Fig. 8.5b), thereafter running posterior to the medial epicondyle of the humerus ●● the radial nerve: originates from the posterior cord of the brachial plexus, winding round the back of the

humerus in the spiral groove between the heads of the triceps (Fig. 8.1b): ●● it is accompanied by the profunda brachii artery, a branch of the proximal brachial artery ●● distal to the spiral groove, the nerve runs between the anterior and posterior compartments (Fig. 8.5c)

then pierces the lateral intermuscular septum (Fig. 8.5d) just above the elbow and continues into the cubital fossa

The Forearm The Bones ●● the radius: is the lateral bone of the forearm, articulating proximally via its head with the capitellum

(radiocapitellar joint) and distally with the carpus (radiocarpal joint): ●● bony landmarks of the radial shaft include the sharp medial interosseous border (Fig. 8.6a), for

attachment of the interosseous membrane (Fig. 8.6b), and the pronator tubercle for insertion of the pronator teres muscle

●● the ulna: is the medial bone of the forearm, articulating proximally with the trochlea (ulnohumeral joint) and distally through the TFCC with the carpus (ulnocarpal joint): ●● bony landmarks of the shaft include the sharp lateral interosseous border (Fig. 8.6a)

●● both bones also articulate with each other at the proximal and distal radio-ulnar joints

Compartmental Anatomy of the Muscles ●● the forearm: contains 2 compartments, volar (anterior) and dorsal (posterior), which are separated by the

interosseous membrane (Fig. 8.6b) ●● the volar compartment: contains the flexor muscles and is divided into superficial, intermediate and deep

muscle groups: ●● the superficial group (Fig. 8.7a): comprises pronator teres (PT), flexor carpi radialis (FCR), palmaris

longus (PL) and flexor carpi ulnaris (FCU), which all arise from the common flexor origin of the medial humeral epicondyle:

● PT has 2 heads, which unite to insert into the pronator tuberosity on the lateral radial shaft ● the remaining muscles insert via tendons into the hand

●● the intermediate group: consists of flexor digitorum superficialis (FDS) (Fig. 8.7a)

●● the deep group: consists of flexor pollicis longus (FPL), flexor digitorum profundus (FDP) and pronator quadratus (PQ):

● FPL originates from the anterior surface of the mid-radial shaft and adjacent interosseous membrane (Fig. 8.7b) and inserts in the hand

● FDP originates from the upper anterior and medial surfaces of the ulnar shaft and adjacent interosseous membrane (Fig. 8.7b) and inserts in the fingers

● PQ originates from the anterior surface of the lower ulna and inserts into the anterior surface of the lower radius (Fig. 8.7c)

●● the dorsal compartment: contains the extensor muscles and comprises lateral, superficial and deep muscle groups: ●● the lateral group: comprises brachioradialis and extensor carpi radialis longus (ECRL) (Fig. 8.8a), both

arising from the lateral supracondylar ridge of the humerus and inserting around the wrist/hand ●● the superficial group (Fig. 8.8b): comprises extensor carpi radialis brevis (ECRB), extensor digitorum

(ED), extensor digiti minimi (EDM) and extensor carpi ulnaris (ECU): ● all arise from the common extensor origin of the lateral humeral epicondyle and insert into the hand/

fingers ●● the deep group (Fig. 8.8c): comprises supinator, abductor pollicis longus (AbPL), extensor pollicis brevis

(EPB), extensor pollicis longus (EPL) and extensor indicis (EI): ● AbPL arises from the posterior surface of the mid-ulna and adjacent interosseous membrane and inserts

into the thumb ● EPL arises from the posterior surface of the radius and adjacent interosseous membrane and inserts into

the thumb

● EPB arises from the posterior ulnar shaft and adjacent interosseous membrane and inserts into the thumb ● EI originates from the posterior surface of the ulna and adjacent interosseous membrane and inserts

into the index finger

The Nerves and Vessels ●● the ulnar artery: is the larger terminal branch of the brachial artery, originating in the cubital fossa:

●● it runs within the anterior compartment of the forearm, proximally lying deep to the flexor muscles (Fig. 8.9) and distally becoming superficial to run between the tendons of FCU and FDS

●● the radial artery: is the smaller terminal branch of the brachial artery, originating in the cubital fossa: ●● within the forearm, proximally it runs deep to brachioradialis (Fig. 8.9) and distally lies on the volar

surface of the radius between the tendons of brachioradialis and FCR ●● the median nerve: enters the forearm by passing between the 2 heads of pronator teres:

●● within the forearm, it runs between FDS and FDP, but is difficult to visualise on MRI due to the paucity of surrounding fat

●● the ulnar nerve: enters the forearm by passing between the 2 heads of FCU: ●● within the forearm, it runs between FCU and FDP (Fig. 8.9)

●● the radial nerve: divides into superficial and deep branches: ●● the superficial branch: within the forearm, runs deep to brachioradialis and lateral to the radial artery

(Fig. 8.9), terminating at the posterior surface of the wrist ●● the deep branch (posterior interosseous nerve): winds around the radial neck within the supinator muscle,

extending into the posterior compartment of the forearm, to run between the superficial and deep muscle groups (Fig. 8.9) to reach the wrist

●● anterior interosseous nerve: is a branch of the median nerve, arising 2-8 cm below the humeral medial epicondyle: ●● within the forearm, it runs just anterior to the interosseous membrane (Fig. 8.9)

The Thigh The Bones ●● the femoral shaft: extends from the lesser trochanter to the femoral condyles and is round in cross-section

anteriorly ●● bony landmarks: a posterior ridge along the femoral shaft, the linea aspera, gives attachment to the medial and

lateral intermuscular septa and various muscles (Fig. 8.10a): ●● the linea aspera diverges distally to form the medial and lateral supracondylar ridges of the femur

(Fig. 8.10b), the medial ridge extending to the adductor tubercle on the medial condyle (Fig. 8.10b)

●● the thigh: contains 3 compartments, anterior, medial and posterior, which are surrounded and contained by the fascia lata (Fig. 8.10a)

●● the anterior compartment is separated from the medial and posterior compartments by the medial and lateral intermuscular septa respectively, which extend from the linea aspera to the fascia lata (Fig. 8.10a)

●● the anterior compartment: contains the tensor fascia lata and iliotibial tract (Fig. 8.11a), sartorius and the quadriceps muscles (rectus femoris, vastus medialis, vastus intermedius and vastus lateralis (Fig. 8.11b), and distally the articular muscle) ●● vastus medialis: arises from the intertrochanteric line and the linea aspera (Fig. 8.11c) ●● vastus intermedius: arises from the anterior and lateral surfaces of the femoral shaft (Fig. 8.11a) ●● vastus lateralis: arises from the intertrochanteric line, the base of the greater trochanter and the linea aspera

(Fig. 8.11a) ●● the articular muscle arises from the anterior distal femoral shaft and inserts into the suprapatellar pouch ●● the quadriceps muscles insert into the quadriceps tendon, and via the patella and patellar tendon, into the

tibial tuberosity ●● the quadriceps muscles are innervated by the femoral nerve, and act to extend the knee joint

●● the medial compartment (Fig. 8.12a): contains gracilis and the adductor muscles (brevis, magnus and longus), which arise from the inferior aspect of the pubis and the inferior pubic ramus: ●● gracilis: runs superficially in the medial thigh to insert into the medial tibia as part of the pes anserinus ●● adductor longus: is the most anterior of the adductor muscles and inserts into the linea aspera ●● adductor brevis: runs deep to adductor longus to insert into the linea aspera ●● adductor magnus: consists of adductor and hamstring portions:

● the adductor portion: inserts into the posterior surface of the femoral shaft ● the hamstring portion: extends distally to insert into the adductor tubercle of the medial femoral

condyle (Fig. 8.10b) ● a gap between the adductor and hamstring portions, the adductor hiatus, allows passage of the femoral

vessels from the thigh to the popliteal fossa

●● the adductor muscles are innervated by the obturator nerve (hamstring portion of adductor magnus by the sciatic nerve), and act to adduct the thigh at the hip and assist in lateral rotation

●● the posterior compartment (Fig. 8.12b): contains the hamstring muscles (semimembranosus, semitendinosus and biceps femoris): ●● semimembranosus, semitendinosus and the long head biceps femoris arise from the ischial tuberosity and

insert around the knee joint ●● the short head biceps femoris arises from the linea aspera and the lateral supracondylar ridge of the femur

(Fig. 8.12c) ●● the hamstrings are supplied by the sciatic nerve and act to extend the hip

The Nerves and Vessels ●● the femoral artery: is a continuation of the external iliac artery and enters the thigh by passing deep to the

inguinal ligament: ●● it continues distally, between the anterior and medial compartments, lying deep to sartorius and anterior

to adductor longus (Fig. 8.13a) ●● it enters the popliteal fossa by passing through the adductor hiatus, where it becomes the popliteal artery

(Fig. 8.13b) ●● the major branch within the thigh is the profunda femoris artery, which arises approximately 4 cm below

the inguinal ligament and runs in the medial compartment (Fig. 8.13a)

●● the sciatic nerve: enters the buttock/thigh through the greater sciatic notch: ●● it runs in the posterior compartment between adductor magnus (anteriorly) and biceps femoris

(posteriorly) (Figs 8.13a, b) ●● in the lower third of the thigh, it divides into its terminal branches, the tibial and common peroneal nerves

(Fig. 8.13c)

The Calf The Bones ●● the tibia: extends from the knee and proximal tibiofibular joint to the ankle:

●● at the junction of the upper tibia with the anterior border is the tibial tuberosity, to which the patellar tendon attaches (Figs 8.14a, b)

●● the tibial shaft is triangular in cross-section, with the anterior and medial borders and the medial surface being subcutaneous (Fig. 8.14c)

●● the lateral border gives attachment to the interosseous membrane (Fig. 8.14c), which separates the anterior from the deep posterior compartments of the calf

●● the fibula: extends from the proximal tibiofibular joint to the ankle (Fig. 8.14a): ●● its medial border gives attachment to the interosseous membrane

Compartmental Anatomy of the Muscles ●● the calf: has 4 compartments, anterior, deep posterior, superficial posterior and lateral ●● the muscle compartments are surrounded by the deep crural fascia and are separated by various septa

(Fig. 8.15a): ●● the anterior and lateral compartments are separated by the anterior intermuscular septum (AIS) ●● the lateral and posterior compartments are separated by the posterior intermuscular septum (PIS) ●● the anterior and deep posterior compartments are separated by the interosseous membrane (IM) ●● the deep and superficial posterior compartments are separated by the transverse intermuscular

septum (TIS) ●● the anterior compartment: contains the tibialis anterior (TA), extensor digitorum longus (EDL) and extensor

hallucis longus (EHL) muscles (Fig. 8.15b): ●● TA: arises from the upper half of the lateral surface of the tibia ●● EDL: arises from the upper 2/3 of the anterior surface of the fibula and adjacent interosseous

membrane ●● EHL: arises from the middle half of the anterior surface of the fibula and the adjacent interosseous

membrane ●● the muscles are all innervated by the deep peroneal nerve

●● the deep posterior compartment: contains the tibialis posterior (TP), flexor digitorum longus (FDL) and flexor hallucis longus (FHL) muscles (Fig. 8.15c): ●● TP: arises from the posterolateral aspect of the tibia, the adjacent interosseous membrane and the posterior

surface of the fibula ●● FDL: arises from the posteromedial aspect of the tibia ●● FHL: arises from the posterior surface of the lower fibula ●● all of the muscles are innervated by the tibial nerve

●● the superficial posterior compartment: contains the gastrocnemius, plantaris and soleus muscles (Fig. 8.15d): ●● gastrocnemius: has medial and lateral heads, arising from the posterior distal femoral metaphysis/condyles

and combining to form the Achilles tendon ●● soleus: arises from the soleal line on the posterior surface of the upper tibia and from the posterior upper

fibula, combining with the gastrocnemius tendon to form the Achilles tendon (Fig. 8.15e) ●● plantaris: runs within the calf between the soleus and gastrocnemius muscles ●● all of the muscles are innervated by the tibial nerve

●● the lateral compartment: contains the peroneal muscles (brevis and longus) (Fig. 8.15f): ●● peroneus longus: arises from the upper 2/3 of the lateral surface of the fibula ●● peroneus brevis: arises from the lower 2/3 of the lateral surface of the fibula ●● both muscles are innervated by the deep peroneal nerve

●● the popliteal artery: divides in the upper calf into the anterior tibial and posterior tibial arteries, the latter giving off the peroneal artery

●● the anterior tibial artery: penetrates the interosseous membrane to enter the anterior compartment of the calf, where it runs with the deep peroneal nerve between the interosseous membrane and the anterior compartment muscles (Fig. 8.16a)

●● the posterior tibial artery: runs in the deep posterior compartment, together with the tibial nerve (Figs 8.16b, c)

●● the peroneal artery: is a large branch of the posterior tibial artery, arising just after its origin and running in the calf behind the fibula (Fig. 8.16c)

●● anatomical variants: of the anterior and posterior tibial arteries arising from the peroneal artery have been described, with implications relating to fibular flap surgery potentially resulting in lower limb ischaemia23

●● the tibial nerve: is the larger branch of the sciatic nerve and runs in the posterior compartment of the calf deep to the gastrocnemius and soleus muscles (Figs 8.16b, c), supplying soleus, FDL, FHL and tibialis posterior

●● the common peroneal nerve: runs in the upper aspect of the lateral compartment (Fig. 8.16d) and after giving off the deep peroneal nerve which runs adjacent to the lateral fibula (Fig. 8.16a), continues as the superficial peroneal nerve within the peroneus longus muscle

●● the sural nerve: runs in the superficial posterior compartment, adjacent to the short saphenous vein (Fig. 8.16e)

●● stress injury: is a term preferred to stress fracture, since not all stress injuries of bone are accompanied by a fracture line

●● stress injuries: may be classified as fatigue or insufficiency fractures, the former resulting from abnormal stress on normal bone, and the latter from normal stress applied to abnormal bone

●● sites of involvement include: ●● the tibia and fibula, accounting for 40-70% of cases and most commonly seen in long-distance runners

and military recruits ●● the foot bones, accounting for 20-35% of cases, most commonly the 2nd and 3rd MTs ●● the neck of femur or femoral diaphysis in ~7% of cases25,28 ●● atypical femoral shaft fractures (AFF) are a recently recognised phenomenon, occurring between the

trochanter and the femoral epicondyles, most commonly originating in the lateral femoral cortex29 ●● stress injuries of the shoulder girdle and upper limbs can be seen in a variety of sporting activities, such as

racket sports, gymnastics, golf, weight-lifting, rowing and throwing,30 and can also occur following the use of crutches

●● transverse/oblique are more common and typically affect the proximal posterior tibial cortex ●● longitudinal stress fractures account for ~10% of tibial stress fractures and typically occur in non-athletes ●● stress fractures of the anterior tibial mid-shaft are less common and have a propensity to non-union and

extension to complete fracture ●● fibular stress fractures: usually affect the distal shaft and account for ~30% of stress fractures in athletes ●● clinically: the diagnosis of stress injury is suggested by the combination of a history of increased physical

activity and appropriate radiological findings: ●● stress injuries are more common in women ●● initially, bone pain is related to increased physical activity, with resolution at rest ●● when the injury becomes more severe, the pain may become constant ●● occasionally, stress fractures may progress to displaced fractures, particularly in the femoral neck ●● proximal tibial stress/insufficiency fractures may mimic meniscal tears and can be identified on knee MRI

(Figs 8.17a, b) ●● non-union/malunion may occur in stress fractures of the tibia, tarsal navicular and 5th MT ●● MRI findings:

●● an MRI classification system has been proposed for stress injuries: ● grade 1: mild periosteal oedema with normal marrow SI ● grade 2: periosteal oedema and increased marrow SI on FS T2W/STIR images but normal T1W

marrow SI (Figs 8.17c, d)

● grade 3: reduced T1W marrow SI with increased FS T2W/STIR marrow SI (Figs 8.17e, f ) ● grade 4: a stress fracture line is present (Fig. 8.18a)

●● grade 4 injuries: were originally divided into grade 4a and 4b, but the relevance of the pattern of grade 4a is uncertain and may be seen in asymptomatic individuals:32

● grade 4a: multiple focal areas of intracortical signal abnormality and bone marrow edema (BMO) visible on both T1W and T2W images

● grade 4b: linear areas of intracortical signal abnormality and BMO visible on both T1W and T2W images

●● transverse tibial stress fracture: appears as a low SI linear band in the proximal metaphysis (Fig. 8.18b), surrounded by oedema on FS T2W/STIR images:

● periosteal reaction and soft-tissue oedema may also be demonstrated (Fig. 8.18c) ●● longitudinal stress fractures: appear as extensive areas of marrow and periosteal oedema (Figs 8.19a, b)

with the fracture line commonly not identified, but when present optimally seen on axial images: ● in the presence of only oedema, the fracture line is demonstrated by CT with MPR (Fig. 8.19c),

which helps to differentiate stress fracture from osteoid osteoma and osteomyelitis ●● anterior tibial stress fractures:33 may appear as focal cortical thickening and adjacent oedema, with a small,

horizontally orientated cortical fracture line occasionally visible (Figs 8.19d, e) ●● subtle MRI findings of mild endosteal oedema have been identified on serial imaging of asymptomatic

army recruits, and are thought to represent adaptive stress changes or remodelling rather than stress injuries, particularly when <10 cm in dimension, while areas of endosteal oedema >10 cm in dimensions may be a manifestation of an early stress response, with potential for progression to a stress injury34

●● thigh splints: is also termed the adductor insertion avulsion syndrome, an avulsive injury of the proximal femoral shaft related to one or more of the adductor muscle insertions

●● clinically: the condition typically affects young athletes, presenting with non-specific hip, groin or thigh pain: ●● examination findings include adductor tenderness and severe pain on resisted hip adduction and external

rotation ●● MRI findings:

●● increased periosteal SI representing traction periostitis along the posteromedial proximal to mid-femoral shaft on STIR images, ranging from 4 cm to 9 cm in length

●● involvement of adductor brevis results in signal changes at the level of the proximal femur, adductor longus at the mid-femoral shaft and adductor magnus slightly more distally

●● associated marrow oedema at the same level is present in 80% of cases ●● increased cortical SI on STIR, indicative of a developing stress fracture (Figs 8.20a, b) ●● changes may be bilateral and resolve completely with conservative management, leaving mild residual

cortical thickening

●● MTSS: represents a group of conditions that present with exercise induced posteromedial tibial pain, referred to generally as ‘shin splints’: ●● risk factors include leg length inequality, running on hard ground, foot pronation during running and pes

planus ●● MTSS may be classified into 3 types:

●● type 1: stress fracture or stress reaction of bone (see above) ●● type 2: periostitis resulting from chronic excessive traction at the periosteal-fascial junction along the tibial

shaft, involving the soleus and tibialis posterior insertions ●● type 3: chronic posterior compartment syndrome (see later)

●● type 2 MTSS: presents with posteromedial distal tibial pain with weakness of the involved muscle ●● MRI findings:

●● type 2 MTSS demonstrates periosteal fluid along the posteromedial aspect of the distal tibia (Fig. 8.21), as seen with grade 1 stress injury/type 1 MTSS

●● however, many patients with type 2 MTSS have a normal MRI appearance

●● pathological fractures: typically occur at sites of bone tumours, either benign or malignant ●● MRI is more accurate in the diagnosis of pathological fracture as opposed to stress fracture, compared with

both radiography and CT ●● MRI findings:

●● a well-defined, focal hypointense T1W marrow signal (Fig. 8.22a) abnormality with corresponding increased SI on STIR/FS T2W FSE images:

● additional features include endosteal scalloping, cortical break, soft-tissue mass and muscle oedema/ haemorrhage (Fig. 8.22b)

●● conversely, the absence of a focal marrow lesion excludes a pathological fracture (Figs 8.22c, d) ●● the presence of mineralisation within the lesion, a soft-tissue mass and cortical lysis at the site of

pathological fracture is more suggestive of a primary bone tumour than a metastatic lesion41

●● osteomyelitis (OM): refers to infection of the bone and bone marrow, and may follow haematogenous spread (haematogenous OM) or develop from direct local invasion of bone

●● haematogenous OM: occurs following bacteraemia from conditions such as urogenital infection, enteritis, cholangitis, endocarditis or from an unknown cause

●● direct spread: may occur following penetrating injuries or may be post-surgical, and is the commonest form of infection complicating diabetes (from plantar ulcers) or in bed-ridden patients (from decubitus ulcers)

●● pathologically: the commonest infecting organism is S. aureus, accounting for 80-90% of cases, 30-40% of these involving community acquired Methicillin-resistant Staphylococcus aureus (MRSA): ●● other organisms include Streptococcus B (in the newborn), pseudomonas (in drug addicts or

immunocompromised patients), Salmonella (in sickle cell anaemia or diabetes) Haemophilus influenzae B in unvaccinated children and Kingella kingae in under 4’s43

●● clinically: acute haematogenous OM occurs most commonly in children, becoming more common again after the age of 50 years: ●● OM in the newborn: is rare and most commonly involves the proximal and distal femoral metaphyses:

● the presence of transphyseal vessels in infants under 18-24 months of age allows spread of infection across the growth plate from metaphyses to epiphyses and then into the adjacent joint, although septic arthritis is more commonly secondary to direct haematogenous synovial seeding

● during early infancy, isolated involvement of the growth plate may occur ●● juvenile OM: localises to the metaphysis and typically extends to the subperiosteal space, since the

avascular growth plate acts as a relative barrier to epiphyseal spread: ● extension into the joint can occur when the metaphysis is intracapsular, as with the hip and knee ● adjacent joint effusions may be reactive in nature, but should always be considered to represent septic

arthritis until proven otherwise44 ●● adult OM: is also relatively rare and when it occurs, most commonly involves the flat bones, the vertebrae

and the diaphyses of long bones: ● extension along the bone can result in a medullary phlegmon ● extension into the epiphysis (Fig. 8.23a) and joint is relatively common, since the growth plate is now

closed, but a subperiosteal abscess is rare ●● MRI findings:

●● the infected marrow space initially shows reduced SI on T1W images (Fig. 8.23a) and increased SI on FS T2W/STIR images (Fig. 8.23b), with diffuse enhancement

●● inflammatory regions are usually large with irregular outlines and areas of preserved medullary fat which may be diffuse or focal (Fig. 8.23c), together with extraosseous fat globules are a characteristic feature, which help to differentiate OM from tumour45

●● intracortical areas of increased SI (Fig. 8.23b), which enhance with gadolinium are also a feature, while central areas of non-enhancement are due to abscess formation and/or sequestra, the latter also being of low SI on T2W/STIR images

●● periostitis and subperiosteal collections are also a feature (Fig. 8.23d) ●● periosseous oedema, optimally identified on axial FS T2W FSE/STIR images (Fig. 8.23b), is almost

invariable ●● intraosseous abscesses are typically well-defined (Figs 8.23e, f ), with a low SI rim on T2W/STIR images

and intense peripheral contrast enhancement ●● if fluid-sensitive sequences are normal, post-contrast studies usually make no additional contribution to

imaging in osteomyelitis: ● an exception is physeal involvement in which the only visible abnormality is increased physeal

enhancement, with no abnormal oedema seen on precontrast T1W or fluid sensitive sequences ●● contrast may also differentiate between a solid inflammatory mass (phlegmon) and abscess formation ●● in children, metaphyseal infections may cross the growth plate (Fig. 8.23g) ●● abnormal marrow signal intensity can persist for several months following successful treatment

●● subacute OM: represents a relatively low-grade infection, which may result from incompletely healed acute OM or may present as a bone abscess termed ‘Brodie’s abscess’

●● pathologically: it is usually 1-4 cm in size, being oval and commonly progressing to intraosseous tunnelling, but rarely resulting in fistula formation

●● it most commonly involves the metaphyses of the lower limbs, can cross the open growth plate in younger patients (Fig. 8.24a) and also the fused growth plate in older individuals to involve the epiphysis

●● S. aureus is the commonest organism, having a predilection for physeal cartilage with cultures being positive in ~50% of cases

●● MRI findings: ●● has the appearances of a bone abscess, with peripheral increased SI on T1W images (penumbra sign)

(Fig. 8.24b), hyperintensity on FS PDW/T2W/STIR images (Fig. 8.24c) and a hypointense rim (Fig. 8.24d), corresponding to medullary sclerosis on radiography

●● the ‘penumbra sign’ is suggestive of, but not pathognomonic for a Brodie’s abscess ●● surrounding marrow oedema is invariable with active lesions (Figs 8.24c, d) and cortical penetration

may result in associated soft-tissue inflammation (Fig. 8.24e) ●● the abscess wall enhances intensely following contrast (Fig. 8.24f) but if the lesion is filled with

granulation tissue, the lesion may enhance more uniformly (Fig. 8.24f)

●● intracortical OM: is relatively rare, appearing as an abscess cavity within an area of cortical thickening, typically demonstrating an enhancing margin and communicating with an adjacent soft-tissue abscess

●● clinically: the femur is most commonly involved, and stretching of the overlying periosteum may be the cause of significant discomfort

●● both clinical symptoms and radiological findings may mimic an osteoid osteoma ●● MRI findings:

●● an elongated intracortical abscess cavity commonly containing an area of signal void due to sequestrum formation (Figs 8.25a, b)

●● medullary and adjacent soft-tissue oedema, and frequently soft-tissue abscess formation (Fig. 8.25c)

●● chronic OM: is defined as symptoms persisting after one month of appropriate antibiotic treatment, and may be classified as primary chronic haematogenous OM or secondary exogenous chronic OM: ●● primary chronic haematogenous OM, without evidence of previous acute/subacute OM, is considered to

be extremely rare ●● however, it is possible that the majority of these cases represent non-bacterial inflammatory bone lesions

●● chronic osteomyelitis: may be secondary to chronic soft-tissue infection or open fractures, the latter becoming infected in approximately 27% of cases, while only 1-2% of joint prostheses become infected

●● pathologically: the condition is characterised by medullary and cortical sclerosis: ●● hyperostosis occurs due to solid periosteal reaction ●● during periods of active infection, the sclerotic areas often contain areas of lysis due to intramedullary/

intracortical abscesses or collections of granulation tissue ●● sequestration and fistulae may also occur

●● MRI findings: ●● signs of active infection include the demonstration of intraosseous abscesses, sequestra and sinus tracts ●● the presence of active infection is suggested by areas of low medullary SI on T1W and increased medullary

SI on FS T2W FSE/STIR images due to oedema (Figs 8.26a, b) ●● granulation tissue surrounding the infection will enhance following contrast

●● other features include: cortical thickening and remodelling, sequestrum formation, sinus tracts and softtissue inflammation/abscesses (Fig. 8.26c):

● cortical sequestra appear as low SI areas on T1W and T2W images (Fig. 8.26d) and cancellous sequestra are relatively hyperintense, showing no enhancement following contrast and possibly requiring CT for demonstration (Fig. 8.26e)

● sinus tracts appear as linear/curvilinear areas of increased T2W SI and post-contrast enhancement extending from the medullary cavity into the soft tissues (Fig. 8.26c)

●● post-traumatic OM: is defined as bone infection that follows skeletal trauma, or complicates the surgical management of skeletal trauma and results from failure of adequate initial antibiotic therapy

●● the commonest causative organism is S. aureus, although Gram negative organisms may be implicated in association with surgical implants

●● 2-6% of open fractures are complicated by OM, of which 15-30% of cases progress to chronic OM, most commonly affecting the tibia and femur

●● the incidence of infection related to surgery and orthopaedic implants is reported as 0.5-2% ●● the role of imaging: in patients with suspected chronic OM is to identify activity of the disease, to determine

the extent of involvement of bone and soft tissue and to identify the presence of sequestra

●● MRI findings: ●● features of active chronic OM include intramedullary and soft-tissue oedema, abscess formation and

sequestrum, as for chronic haematogenous OM (Figs 8.26a-e) ●● conversely, absence of increased SI on FS T2W FSE/STIR images excludes active disease (Figs 8.27a, b) ●● difficulty in the diagnosis of active infection relates to the presence of abnormal T2W SI and post-contrast

enhancement of the marrow in patients who have suffered bony trauma or undergone surgery: ● such changes are due to reparative granulation tissue, and may persist for up to 12 months following surgery ● granulation tissue initially enhances uniformly, but with time the enhancement becomes peripheral,

leaving a relatively hypovascular central scar ● enhanced MRI is reported to have a sensitivity and specificity of 84% and 60%, respectively, in

diagnosing chronic post-traumatic OM ● the presence of sinus tracts increases the diagnostic confidence of active infection ● marrow SI alterations may also be due to susceptibility artefact from residual metallic fragments or the

presence of instrumentation

●● the incidence of musculoskeletal TB is once again rising, in part due to the increased incidence of AIDS ●● pathologically: haematogenous spread from a primary or reactivated focus in another part of the body (lung,

meninges, lymphatic system) is the commonest cause: ●● haematogenous spread to the medullary cavity results in granuloma formation, enlargement with

caseation and bone destruction

●● TB OM occasionally follows direct spread from soft-tissue infection and can also occur following BCG vaccination

●● prosthesis-related TB OM and septic arthritis may present in patients with a history of previously treated skeletal or extraskeletal TB, and has also been reported in cases with no known history of TB

●● TB may affect the axial skeleton (see Chapter 9), joints, tendon sheaths and bursae (see Chapter 7) and the bones of the appendicular skeleton, resulting in TB OM

●● cystic TB:52,53 is a subcategory of TB usually affecting children and young adults: ●● it typically affects the metaphyses of long bones, but flat bones including the skull may be involved

●● extra-axial TB OM: is usually monostotic, but multi-focal TB may occur in immunocompromised patients such as the elderly, AIDS patients, or those on chemotherapy

metacarpals, commonly with associated periostitis ●● with progression of infection, intra-articular cystic spaces develop resulting in bone expansion, a condition

referred to as ‘spina ventosa’ ●● TB granuloma: of bone is an uncommon solid focal lesion, which may mimic a bone tumour ●● clinically: TB OM differs from pyogenic OM in the relative absence of symptoms such as fever and pain,

typically having a very insidious onset, and any bone can be affected: ●● a paradoxical reaction (PR) refers to worsening of the infection that rarely follows initiation of therapy ●● HIV-positive status, disseminated TB and commencement of highly active anti-retroviral treatment

(HAART) are risk factors, but the phenomenon can occur in any patient group54 ●● MRI findings:

●● similar to those seen with pyogenic OM ●● reduced marrow SI on T1W images with increased SI on FS T2W FSE/STIR images (Figs 8.28a, b) ●● enhancement of the marrow following contrast (Figs 8.28c, d) ●● bone abscess may eventually develop (Fig. 8.28e), with/without associated soft-tissue involvement

(Figs 8.28c, d) ●● cystic TB: multiple round/ovoid lesions with sclerotic margins, occasionally associated with bone

expansion: ● metaphyseal lesions may cross the growth plate to involve the epiphysis, potentially resulting in physeal

damage, bone bar formation and growth arrest, although careful curettage can minimise damage to the growth plate55

●● TB dactylitis: bone expansion with reduced T1W SI, increased SI on FS T2W FSE/STIR images, periostitis and soft-tissue swelling (Figs 8.28f, g)

●● TB granuloma of bone: non-specific bone lesion with associated marrow oedema-like SI (Figs 8.28h, i)

●● fungal infections: that can result in OM include cryptococcosis, candidiasis, aspergillosis, coccidioidomycosis, maduromycosis, blastomycosis and histoplasmosis

●● musculoskeletal involvement is uncommon and is predisposed to by conditions such as immunosuppression, DM, sickle cell disease and AIDS

●● infection may be mild and chronic, with certain pathogens limited by distinct geographic distribution ●● infection typically results from skin inoculation or haematogenous spread from a distant focus, usually the

lungs ●● clinically: features that suggest a fungal infection include a skin sinus, chronic multi-focal OM, soft-tissue

nodules and chronic granulomatous joint involvement: ●● tendon and muscle involvement is uncommon, but presents with chronic nodular tenosynovitis or

granulomatous tenosynovitis with abscess formation ●● cryptococcosis: is caused by Cryptococcus neoformans, a fungus that is distributed throughout the world:

●● bone and joint infection occurs secondary to haematogenous spread following inhalation into the lungs, and occurs in 5-10% of cases

●● sites of infection include the spine, pelvis, ribs, skull, tibia and knees

●● OM presents as focal lytic lesions with minimal or no surrounding sclerosis, occasionally spreading to involve the adjacent joint

●● AVN of the larger joints has been described ●● candidiasis (moniliasis): most commonly results from Candida albicans, as an opportunistic infection typically

in patients with central lines or intravenous drug abusers: ●● OM is a rare feature of disseminated disease and most commonly affects the pelvis, sternum, scapula,

spine and ribs, resulting in an osteolytic lesion with no periosteal reaction, and has a predilection for larger joints

●● aspergillosis: caused by Aspergillus fumigatus is almost exclusively confined to the immunocompromised patient: ●● bone involvement is extremely rare, usually involving the spine and ribs, but has been described in other

bones, including the hands and feet, presenting with a granulomatous polyarthritis ●● coccidioidomycosis:57 a systemic fungal infection caused by Coccidioides immitis, which is endemic to the

south-western USA, Mexico and parts of South America: ●● infection occurs in the lungs and is commonly asymptomatic ●● 0.5-1% of patients may suffer disseminated disease, with OM or septic arthritis occurring in 10-50%

of these ●● the spine, ribs, sternum, pelvis and skull are most commonly involved ●● extraspinal involvement frequently involves long bone metaphyses, osseous protuberances such as the

trochanters, ischial and iliac spines with diaphyseal involvement more common in the hands and feet ●● long bone OM results in punched out lesions, with a more moth-eaten appearance in smaller bone, usually

with no periosteal reaction: ● when present, sclerosis represents a healing response in treated lesions

●● joint involvement is as a monoarthritis or reactive polyarthritis, commonly involving the knees and ankles ●● imaging reveals a granulomatous arthritis that mimics TB, which may be associated with focal soft-tissue

cyst formation ●● maduromycosis (mycetoma): a chronic granulomatous fungal infection caused by various actinomycetes:

●● it is prevalent in India, sub-Saharan Africa, the southern Arabian peninsula and central/south America ●● the disease typically follows a thorn prick and affects the lower limb in 70-75% of cases ●● initial skin infection spreads to the bones, resulting in erosion, deep sinuses and abscesses ●● foot involvement is common, presenting as nodular thickening of the plantar surface, granuloma

involvement involving the adjacent bones and pus-discharging via multiple skin sinuses ●● histoplasmosis: caused by Histoplasma capsulatum, occurring in the Mississippi valley of the USA or by

H. duboisii, present in Africa: ●● skeletal involvement results in radiological features which mimic TB and sarcoidosis, with involvement of

the flat bones, ribs and small tubular bones of the hands and feet ●● blastomycosis: endemic in the mid-western United States:

●● skeletal infection usually involves the thoracic and lumbar spine and lower limbs ●● OM of the long bones appears as a focal eccentric osteolytic lesion, that may mimic a bone tumour ●● joint involvement manifests as joint space narrowing, marginal erosions, synovial swelling and focal

osteopenia ●● sporotrichosis: is a contaminant of wood and soil and most commonly presents as a deep soft-tissue fungal

infection of the extremities: ●● inoculation is usually through scratches to the hands and feet, resulting in soft-tissue infection with

multiple sinuses ●● contiguous or lymphatic spread to bone results in proliferative and sclerotic bone lesions with appearances

similar to other causes of sclerosing osteomyelitis such as TB or Brodie’s abscess ●● Lyme disease (Borrelia burgdorferi): a tick-born spirochete infection in which musculoskeletal involvement

presents with large joint effusion, with progression to synovitis and cartilage loss in late stages58 ●● parasitic infections: rarely involving the musculoskeletal system include toxoplasmosis (Toxoplasma gondii),

giardiasis (Giardia lamblia) and hydatid disease (Echinococcus granulosus): ●● musculoskeletal hydatid occurs in 0.5-4.7% of cases, with 60% occurring in the spine, pelvis and hips

joints, 28% in the long bones

●● melioidosis (Burkholderia pseudomallei) is a multi-system infectious disease: OM, septic arthritis, pyomyositis and soft-tissue abscess formation are recognised features of the disease, which should be suspected in cases with co-existing splenic and hepatic abscess formation

●● MRI findings: ●● fungal OM results in appearances that are essentially indistinguishable from chronic pyogenic OM ●● hydatid disease: may result in cystic bone expansion, which may be unilocular or multilocular:

● the cysts are hypointense on T1W and hyperintense on T2W, with the peripheral rim showing high SI in its outer part and low SI in its inner part on T2W

●● CRMO: is a disorder of unknown aetiology, which typically affects children and adolescents (females more than males), and is considered to represent the childhood equivalent of the SAPHO syndrome61

●● it is a diagnosis of exclusion based on the following criteria: ●● bone lesions with a radiographic picture similar to subacute/chronic OM ●● common involvement of the medial clavicle and frequently multi-focal ●● absence of abscess, fistula and sequestrum formation, with no growth on microbiological investigation ●● a characteristic clinical course with recurrent episodes of pain occurring over several years, while non-

recurrent sterile osseous lesions are termed non-bacterial osteitis (NBO)62 ●● occasional associated skin disease, most commonly palmoplantar pustulosis (PPP) and less commonly acne

or psoriasis ●● lesions typically involve the medial 1/3 of the clavicle, the metaphyses of the long bones, the spine

(see Chapter 9) and pelvis ●● involvement of the mandible, sternum/manubrium, ribs, small bones of the hands/feet is also well recognised ●● lesions are commonly multiple and symmetrical, but a single bone may also be affected ●● clinically: CRMO results in pain and swelling, with occasional malaise and low-grade fever:

●● the duration of symptoms is usually 7-25 years ●● it is a self-limiting condition with few long-term osseous sequelae, but may result in premature growth-

plate fusion and consequent limb shortening ●● MRI findings:

●● whole body MRI comprising coronal T1W and STIR sequences is a sensitive means of detecting multifocal lesions, which may be asymptomatic63 and also in monitoring treatment response (Figs 8.29a, b)

●● long bone lesions: destructive metaphyseal lesions eccentrically located adjacent to the growth plate (Figs 8.29c-e):

● associated bone marrow oedema is seen with active lesions and mild periosteal/soft-tissue oedema may be demonstrated (Fig. 8.29d)

● marrow changes revert to normal as the lesions heal ● spread to the metadiaphyseal region can occur with repeated periostitis resulting in cortical

hyperostosis (Fig. 8.29f) ●● clavicular lesions: medullary lytic lesions in the medial third-to-half, with associated marrow oedema

(Figs 8.30a, b): ● periosteal reaction, which may be multi-laminated (Fig. 8.30c) ● surrounding soft-tissue swelling but no soft-tissue mass or abscess formation ● progressive healing and reactivation result in medial clavicular hyperostosis (Fig. 8.30d)

●● flat bone lesions: may present as foci of marrow oedema without abscess formation/bone destruction (Fig. 8.31a), destructive lesions at joint surfaces or synchondroses, or predominantly sclerotic lesions (Fig. 8.31b)

●● benign tumours: local imaging of the lesion including the nearest joint is sufficient ●● primary malignant tumours: high resolution imaging of the local disease plus imaging of the whole bone for

assessment of ‘skip’ metastases

●● local staging: can be subdivided into intraosseous and extraosseous extent ●● intraosseous extent: coronal T1W SE sequences allow accurate assessment of the longitudinal extent of

marrow involvement (Fig. 8.32a), with the addition of a coronal STIR sequence optimally demonstrating tumour associated reactive marrow oedema (Fig. 8.32b): ●● relationship of tumour to the growth plate is important in children, since disease not involving the physis

may allow joint sparing reconstruction (Fig. 8.32c)

●● coronal T1W SE image of the whole bone allows assessment of ‘skip’ lesions (Fig. 8.32d): ● a ‘skip’ lesion is a metastasis occurring in the same bone as the primary lesion but separated from it by a

region of normal uninvolved marrow ● a transarticular skip lesion is a metastasis occurring in the bone on the other side of the joint from the

primary tumour (Fig. 8.32e), and prognostically is considered to represent a distant metastasis ●● extraosseous extent: requires assessment of the relationship between extraosseous tumour and the

neurovascular bundle, adjacent joint and muscle groups and is optimally assessed on a combination of axial PDW/FS PDW FSE sequences, which allow excellent tissue contrast between tumour, bone cortex, muscle, fat and the neurovascular bundle: ●● the neurovascular bundle: may be clear of tumour (Fig. 8.33a), in contact with/displaced by tumour

(Fig. 8.33b) or partially/completely encased by tumour (Fig. 8.33c) ●● involvement of the joint can be assessed on a variety of sequences and is diagnosed if there is:

● extension of solid tumour tissue into the joint space (Figs 8.33d, e) ● pathological fracture involving the joint (Fig. 8.33f) ● the presence of a joint effusion alone is a poor predictor of joint involvement

●● peritumoural marrow and soft-tissue oedema: are relatively common findings, which in themselves do not distinguish benign from malignant lesions, being related to tumour prostaglandin production: ●● however, the greater the ratio of marrow oedema extent to lesion size, the more likely the lesion will be

benign65

●● bone islands: are hamartomatous lesions located in the medullary cavity, most commonly identified in the pelvis, ribs and the metaphyses/epiphyses of the femur

●● clinically: they are asymptomatic and usually identified incidentally, being seen in all age groups with no gender bias: ●● they are present in approximately 14% of cadaveric studies

●● pathologically: they are single or multiple lesions ranging from 1 to 20 mm in diameter, with larger lesions being termed ‘giant bone islands’, which may be symptomatic: ●● multiple lesions occur in the setting of osteopoikilosis or osteopathia striata, both autosomal dominant

conditions in which rounded (osteopoikilosis) or elongated (striata) lesions are identified in a periarticular distribution

●● MRI findings: ●● lesions have the characteristics of cortical bone within the medullary cavity, appearing as foci of signal

void on all pulse sequences, without associated marrow oedema (Fig. 8.34a) ●● the margins of the lesion may be spiculated, merging with the surrounding trabeculae (Fig. 8.34a) ●● when located in long bones, the long axis of the lesion follows that of the bone (Fig. 8.34b) ●● multiple periarticular lesions characterise osteopoikilosis (Fig. 8.34c) ●● lack of growth on serial imaging is helpful in the differentiation from sclerotic metastases, and growth of

more than 25% in a year is an indication for a biopsy

●● osteomas: are benign tumours or hamartomas composed of dense mature lamellar/compact bone, most commonly arising on the external surfaces of the membranous bones of the skull or paranasal sinuses, but occasionally involving other bones

●● they are usually solitary but may be multiple in conditions such as Gardeners syndrome, (associated with intestinal polyps, fibromata, desmoid tumours and epidermal cysts), or tuberous sclerosis

●● clinically: they are usually asymptomatic and identified incidentally, although they may present as bony masses (parosteal osteomas)

●● pathologically: central or medullary osteomas are associated with the endosteum (Figs 8.35a, b), do not have a spiculated margin and do not blend with the surrounding bone, in contrast to enostoses: ●● parosteal osteoma: may mimic the solid periosteal reaction seen with osteoid osteoma, and a small nidus

should be excluded with high resolution CT ●● characteristics more suggestive of a parosteal osteosarcoma than a juxta-cortical osteoma include:

a metaphyseal location, heterogeneous T2W signal, soft-tissue mass, periosteal reaction and lucent cleavage plane between the lesion and the underlying bone on plain radiographs

●● MRI findings: ●● well-defined, low SI lesions on all pulse sequences arising either within (Figs 8.35a, b) or on the surface

of the bone (Figs 8.35c, d) ●● they are usually ~3 cm in diameter with no associated periosteal or soft-tissue reaction

●● osteoid osteoma (OO): is a benign osteoblastic lesion, which represents approximately 10% of all biopsied benign bone tumours

●● many different bones can be affected but the long bones are the commonest site with more than two-thirds involving the femur and tibia, usually the diaphysis but also the femoral neck, while approximately 10% are intra-articular

●● the natural history of OO: involves a gradual burn-out of the lesion which can take as long as 3 years, and although conservative management may be successful,71 treatment is usually sought in the early stages due to the severity of symptoms

●● pathologically: the tumour consists of a small (<1.5 cm), richly innervated vascular nidus composed of osteoid and woven bone with variable calcification: ●● there is a surrounding host response comprising reactive marrow/soft-tissue oedema, medullary sclerosis

and periosteal reaction ●● long bone lesions are typically intracortical, whereas medullary lesions are usually found in the small bones

of the hand and foot, and the epiphyses of long bones ●● subperiosteal lesions may also be seen, typically in the femoral neck

●● clinically: OO is seen in all age groups but most commonly in the first 3 decades of life: ●● typical symptoms include a dull ache, which is worse at night and relieved by NSAIDs ●● intra-articular lesions present as monoarthropathy with joint effusion and synovitis

●● MRI findings: ●● the nidus shows intermediate SI on T1W (Fig. 8.36a) and variable SI on T2W/STIR images depending

upon the degree of fibrosis/mineralisation72 (Fig. 8.36b), and intense enhancement following gadolinium (Fig. 8.36c)

●● reactive changes: reactive bone and soft-tissue changes are reported to occur in 77% and 86% of cases respectively,73 and include:

● medullary sclerosis (reduced SI on T1W and T2W images) and oedema (reduced SI on T1W and increased SI on FS T2W/STIR images) (Fig. 8.36d):

● periosteal reaction (Figs 8.36e, f ) and soft-tissue oedema/reactive soft-tissue mass (Fig. 8.36g) ● reactive changes are typically more florid in younger patients (Fig. 8.36h)74 ● feeding vessels may be visible on CT and MRI, which may be helpful in characterising less typical lesions75

●● intra-articular lesions:76 demonstrate in addition, a joint effusion due to synovitis and periosteal response, which will be adjacent to the joint:

● typical locations include the femoral neck (Figs 8.37a, b), especially the medial aspect and the distal humerus adjacent to the olecranon fossa (Fig. 8.37c)

● subtle abnormalities of the overlying articular cartilage may be demonstrated with T2 mapping77 ●● the ability of MRI to demonstrate the nidus depends upon the imaging technique, particularly the

relationship between slice thickness and nidus dimensions: ● unenhanced MRI potentially misses 35% of OO73 ● improved lesion detection may be achieved using dynamic-enhanced MRI compared to

non-enhanced MRI, demonstrating rapid wash-in and rapid wash-out or a plateau pattern of contrast enhancement, with the greatest enhancement occurring in the first 90 seconds

● high spatial resolution dynamic enhanced MRI can reliably identify the OO nidus, and is particularly useful in cases where the nidus cannot be identified on plain radiographs or CT78

● dynamic contrast-enhanced MRI can also identify OO recurrence after percutaneous ablative treatment, with the recurrent lesion displaying similar perfusion characteristics to those seen prior to treatment, and these findings may even be apparent prior to the recurrent lesion becoming symptomatic79

●● following percutaneous thermocoagulation: sclerosis of the nidus may be seen (Fig. 8.37d), and the presence of residual marrow oedema-like SI does not necessarily indicate treatment failure (Fig. 8.37e)80

●● MR-guided percutaneous laser ablation: is emerging as a novel technique for the treatment of OO, having the benefit of real time thermal imaging to monitor tissue temperature and not carrying a radiation dose burden81

●● osteoblastoma (OB): is a benign, though locally aggressive tumour histologically similar to OO but larger, the nidus being >1.5-2 cm in dimension

●● it is a rare lesion, accounting for <1% of all primary bone tumours and is usually seen in young adults, being more common in males (approximately 2:1)

●● the femoral diaphysis is the commonest long bone site, but any bone can be affected ●● pathologically: it may show local extension through the bony cortex, with surrounding reactive oedema and

sclerosis: ●● secondary aneurysmal bone cyst (ABC) change is recognised, and rarely aggressive/malignant variants

occur which have the potential to metastasise ●● aggressive lesions tend to be larger, occur in older individuals and have more prominent mitotic activity ●● <1% of OB undergo malignant transformation into osteosarcoma

●● MRI findings: ●● the tumour is predominantly lytic with intermediate T1W/T2W FSE SI (Figs 8.38a, b) and increased FS

T2W/STIR SI (Fig. 8.38c) with heterogeneous enhancement seen following contrast ●● focal areas of signal void and heterogeneity may occur due to matrix mineralisation, and a sclerotic margin

is present in 90% of cases ●● secondary ABC change: is manifest by the presence of cystic areas containing fluid levels, seen in

10% of OB ●● reactive changes in the form of marrow/soft-tissue oedema and periostitis are also typical (Figs 8.38a-c) ●● however, unlike OO, an extraosseous soft-tissue mass may be due to tumour extension rather than

reactive soft-tissue swelling

●● conventional central OS: is the second commonest primary malignant bone tumour following multiple myeloma

●● it is also termed intramedullary high-grade OS and accounts for ~75% of all types of OS ●● clinically: it most commonly presents in the second decade of life, being rare in patients under 6 and over

60 years of age: ●● ~10% occurring after the age of 40 years, more frequently arising in flat bones or as secondary

degeneration of pre-existing lesions ●● pathologically: it typically arises in the metaphyses of long bones (distal femur>proximal tibia>proximal

humerus>proximal femur), but diaphyseal and epiphyseal extension are not uncommon: ●● primary diaphyseal OS: represents 2-11% of cases, occurs in an older age group, is often larger at diagnosis

and has more prominent osteolytic features,83 while primary epiphyseal OS is very rare ●● histologically: the predominant subtype may be osteoblastic, chondroblastic or fibroblastic but the mixed

variety is most common, accounting for the mixed radiographic densities and MRI signal intensities ●● lytic (osteoclast-rich) OS is a further subtype ●● most lesions are approximately 8-10 cm in length at presentation and have extended through the cortex to

form an extraosseous mass, which may or may not be limited by the periosteum ●● intra-articular extension is most commonly seen with distal femoral lesions, typically in the region of the

posterior capsule, the intercondylar notch (related to the ACL), or into the suprapatellar pouch ●● ‘skip’ metastases: occur in approximately 8-10% of cases of appendicular OS and are associated with a

poorer prognosis, due to the frequency of co-existing distant metastases84 ●● MRI findings:

●● depending on the stage of presentation, tumour tissue may involve part (Figs 8.39a, b) or all (Fig. 8.39c) of the transverse extent of the medullary cavity

●● the tumour is typically of mixed intermediate SI on T1W images (Fig. 8.32a) and intermediate/increased SI on FS T2W/STIR images (Fig. 8.32b)

●● areas of low SI may be due to predominantly osteoblastic tissue or regions of fibrosis (Figs 8.39a, b), whereas areas of increased SI may represent subacute haemorrhage

●● extension of tumour across an open growth plate is a relatively common finding (Fig. 8.39d)

●● ‘skip’ lesions: appear as foci of similar SI characteristics to the main tumour, separated from the main tumour by a region of normal marrow (Fig. 8.39e)

●● extraosseous tumour may be either concentric (Fig. 8.39f) or eccentric (Figs 8.39a, b), and may show spiculated, linear low SI on PDW/T2W images (Fig. 8.39f) consistent with the vertical (sunburst) periosteal reaction seen on radiographs

●● small areas of fluid level change, typically representing less than a third of the tumour volume are relatively common in conventional OS (Fig. 8.39b)85

●● heterogeneous enhancement is seen following contrast (Fig. 8.39g), although routine use of gadolinium is not required

●● peritumoural oedema will also enhance following contrast (Fig. 8.39g) and therefore, conventional postgadolinium T1W imaging is of no value in differentiating peritumoural oedema from extraosseous tumour

●● however, oedema can be differentiated from extraosseous tumour using dynamic enhancement techniques, which can also facilitate in determining the response to chemotherapy86

●● post-treatment imaging: ● following the use of granulocyte-colony stimulating factor (GCSF), extensive areas of marrow

hyperplasia may become evident and should not be mistaken for tumour extension, a potential pitfall on conventional T1W SE and high b-value diffusion weighted sequences10

● MRI volumetry shows promise as an indicator of treatment response87

●● telangiectatic OS: is an uncommon aggressive form of central OS accounting for 3.5-11% of cases, affecting the same locations as conventional OS and occurring in the same age group

●● pathologically: the tumour is expansile and lytic, being composed of multi-locular blood filled cavities, divided and surrounded by thick septa containing malignant cells

●● telangiectatic OS may present following dedifferentiation of other primary tumours, including parosteal osteosarcoma90 and chondrosarcoma:91 ●● imaging features suggesting dedifferentiation include lytic changes and fluid levels in osseous cavities

●● the haemorrhagic nature of the lesion may result in areas of increased SI on both T1W and T2W images (Figs 8.40a, b)

●● extensive areas of cystic/fluid level change are characteristic, mimicking ABC (Figs 8.40b, c) ●● post-contrast MRI may help in differentiating from ABC by demonstrating areas of peripheral or nodular

septal enhancement due to solid tumour tissue

●● small cell OS: is a rare lesion accounting for approximately 1% of all OS ●● the clinical and imaging features are similar to those of conventional OS, but pathologically, the tumour is

composed of small round cells, similar to Ewing sarcoma

●● pseudocystic OS: is a rare form of high-grade central OS, which radiologically resembles either simple bone cyst (SBC) or ABC, being purely lytic and expansile with no associated periosteal reaction

●● MRI findings: ●● an expansile bone lesion with heterogeneous intermediate SI on T1W and intermediate/high SI on T2W

images (Figs 8.41a, b) and no extraosseous tumour mass

●● LGCOS: is a rare lesion comprising less than 1% of all OS ●● clinically: the mean age at presentation is ~30 years, with equal male to female ratio and patients typically

have a long period of symptoms prior to presentation

●● most cases occur in the metaphyses around the knee, with two-thirds involving the distal femur or proximal tibia: ●● other bone involvement is rare, but extension into the epiphysis and diaphysis is relatively common

●● radiological features: can mimic those of fibrous dysplasia (Figs 8.42a, b), osteoblastoma or non-ossifying fibroma, with over 60% of lesions being lytic with trabeculation (Fig. 8.42c), and the remainder being densely sclerotic or mixed in nature

●● pathologically: LGCOS is a well-differentiated intramedullary lesion, which is histologically the same as parosteal osteosarcoma

●● MRI findings: ●● bone expansion (Figs 8.42a, b) and extraosseous extension (Fig. 8.42d) are common findings ●● the SI characteristics will be variable depending upon the relative lytic/sclerotic components ●● fluid levels are not reported and reactive medullary changes are not a prominent feature (Fig. 8.42c) ●● the presence of cortical destruction, soft-tissue extension and periosteal reaction distinguish LGCOS from

benign fibroosseous lesions

●● intracortical OS: represents the rarest form of OS, accounting for less than 1% of all cases ●● in contrast to other OS subtypes, intracortical OS typically arises in the diaphysis ●● it occurs in the femur or tibia as an intracortical lytic lesion without gross intramedullary extension ●● the age range of reported cases is 10-43 years, most occurring in the 2nd decade ●● MRI findings:

●● it has non-specific SI characteristics, the lesion being limited to the cortex ●● it may be associated with peritumoural and medullary oedema, the latter being associated with

microscopic intramedullary tumour extension ●● the imaging findings are similar to those of an OO, but the margins of OO are typically better defined

and associated with more florid marrow and soft-tissue oedema

●● juxta-cortical (surface) OS: account for 3-6% of OS and comprise periosteal, parosteal and high-grade surface OS

●● they arise from the bone surface or periosteum, and are further subclassified by histological features and grade

●● periosteal OS: represents 1-2% of all OS, 25% of surface OS and presents in an older age range than conventional OS (mean age 20 years)

●● 85-95% involve the distal femoral or proximal tibial metadiaphysis, typically arising on the anteromedial portion of the bone

the periosteum ●● MRI findings:

●● the lesion is typically oval with an average longitudinal dimension of ~8 cm ●● the tumour appears as a broad-based soft-tissue mass attached to the cortex (Figs 8.43a, b), commonly

with associated cortical scalloping and spiculated periosteal reaction (Fig. 8.43b) ●● chondral-type matrix mineralisation may be evident ●● the tumour is typically isointense to muscle on T1W images (Fig. 8.43a) and heterogeneous and

hyperintense on PDW/T2W/STIR images (Fig. 8.43b) ●● the soft-tissue margin is typically well-defined, with or without a pseudocapsule

●● 75% of cases show areas of abnormal adjacent marrow SI consistent with oedema (Fig. 8.43c), but malignant infiltration of the marrow is rare:

● when the intervening cortex is intact and such foci are not continuous with the soft-tissue mass, there is no pathological evidence of intramedullary tumour

● if the cortex is abnormal, SI in the marrow may represent tumour invasion ●● following contrast, variable enhancement is seen, which may be peripheral/septal as is typically seen with

chondral tumours or more uniform (Fig. 8.43d) ●● differentiation between periosteal OS and high-grade surface OS may be challenging, but the latter often

involves the entire bone circumference and is more likely to show medullary invasion

●● POS: is the commonest of the surface OS and accounts for 3-4% of all OS ●● clinically: it occurs in an older age group with a peak incidence in the 3rd-4th decades, being slightly more

common in females: ●● older patients are more likely to present with a higher-grade lesion, and such lesions are larger than low-

grade tumours ●● the commonest site is the posterior metaphysis of the distal femur (60% of cases), followed by the proximal

tibia and proximal humerus ●● pathologically: it consists of heavily mineralised/ossified lobular masses arising from the outer fibrous layer of

the periosteum: ●● a cleavage plane or ‘string sign’ represents an interval between the mass and the underlying normal cortex,

seen in 65% of cases on cross-sectional imaging, while in other cases cortical thickening and fusion between the mass and cortex may be evident

●● most are low-grade tumours (grade 1), treated by primary surgical excision, but higher grade POS (grade 2 or 3) and dedifferentiation to high-grade OS (dd-POS) may occur, the latter requiring neo-adjuvant chemotherapy and carrying a prognosis similar to that of conventional high-grade central OS

●● high-grade areas may be seen in 22-64% of cases ●● MRI is useful for assessing the grade of tumour and identifying intramedullary extension, which occurs in

approximately 40% of low-grade and 50% of high-grade tumours, but is not thought to be related to the overall prognosis

●● MRI findings: ●● the classical low-grade lesion appears as a lobular mass applied to the cortex of the bone, with very low SI

on all pulse sequences due to heavy mineralisation (Figs 8.44a, b) ●● 70% of tumours have a cortical attachment of at least 1 cm and 80% involve 50% or less of the bone

circumference, with the tumour having a tendency to wrap around the involved bone with growth102 ●● intramedullary extension is demonstrated as continuity of tumour through the cortex (Fig. 8.44c) ●● areas of soft-tissue SI (intermediate T1W and increased PDW/T2W) >1 cm3 are indicative of the presence

of high-grade tumour or dd-POS (Figs 8.44d-f)

●● HGSOS: is the least common of the juxta-cortical OS, accounting for less than 1% of all OS and 8-10% of surface OS

●● clinically: it usually affects adolescents and young adults in the 2nd-3rd decades of life, and the lesion involves the metadiaphyseal regions of the femur, humerus and tibia, most commonly located within the diaphysis

●● HGSOS: is a broad-based moderately-densely ossified lesion, usually lacking the spiculated periosteal reaction seen in periosteal OS

●● pathologically: it arises from the bone surface and is histologically indistinguishable from conventional central OS, with a similar management and prognosis

●● MRI findings: ●● it appears as a broad-based surface lesion with low/intermediate T1W SI and intermediate/high T2W SI

(Figs 8.45a-c) ●● heterogeneous areas of low SI may be seen due to matrix mineralisation ●● erosion/destruction of the underlying cortex may occur, with frank intramedullary extension present in

8-48% of published cases (Figs 8.45a, b)103,104 and does not appear to influence overall survival

●● multi-centric OS: is also termed osteosarcomatosis and represents the occurrence of OS at multiple sites, which may be either synchronous or metachronous

●● it is unclear whether this condition represents multiple primary tumours, or the presence of bone metastases from a primary OS

●● MRI findings: ●● multiple foci of disease are identified, but patients often present with only one symptomatic site, and the

remainder identified on staging studies

●● (en)chondroma: is a benign intramedullary tumour, being the 2nd commonest benign bone tumour after osteochondroma and accounting for 3-17% of all primary bone tumours in large biopsy series

●● previously thought to occur as a result of misplacement of embryonic physeal cartilage into the metaphysis, more recent studies have identified an association with specific genetic mutations, suggesting that enchondromas are neoplastic lesions

●● clinically: it usually presents as an incidental finding on radiographs/MRI studies, or with pathological fracture in the small tubular bones: ●● enchondroma is identified as an incidental finding in 2.9% of knee MRI studies (Figs 8.46a, b)

●● the commonest locations are the metacarpal and phalangeal diaphyses (Fig. 8.46c) of the hand (40-65%) and the long bones including the femur, humerus and tibia (25%)

●● pathologically: the neoplasm is composed of lobules of hyaline cartilage, with variable matrix mineralisation seen in ~95% of cases: ●● long bone lesions typically arise centrally or eccentrically in the metaphysis or diaphysis, while 2-5% of

cases are located within the epiphysis, the latter usually involving the proximal humerus or distal femur and typically with a sclerotic margin (Fig. 8.46d)

●● the term ‘endosteal enchondroma’ is used for lesions located in a subcortical location, which can be associated with marked endosteal scalloping (Figs 8.46e, f )

●● enchondromas are usually less than 6 cm in length ●● MRI findings:

●● appear as well-defined, lobular lesions with intermediate SI on T1W (Fig. 8.47a) and variable increased SI on PDW/T2W FSE images (Figs 8.47b, c), with areas of signal void due to calcification and T1W hyperintensity due to trapped yellow marrow (Fig. 8.47d)

●● on FS PDW/T2W FSE/STIR (Figs 8.46b, c) and T2W GRE images (Fig. 8.46d), the lesion is markedly hyperintense

●● peripheral and/or septal enhancement is typical following gadolinium (Fig. 8.47e) ●● larger lesions may show a variable degree of endosteal scalloping, but marrow oedema and periosteal

reaction are rare

●● Ollier’s disease: or enchondromatosis, represents a rare, non-hereditary condition characterised by multiple foci of intramedullary and intracortical cartilage: ●● Ollier’s commonly involves only/predominantly one side of the body ●● the long bones are usually affected, with deformity and shortening, although lesions may also be seen in

the hands, feet and pelvis ●● transformation to chondrosarcoma is thought to occur in ~5-30% of cases

●● enchondromatosis: associated with soft-tissue haemangiomas is termed Maffucci’s syndrome, which may also be associated with soft-tissue lymphangiomas: ●● the soft-tissue abnormality usually affects the same limb as the enchondromatosis and involvement of the

hand and wrist predominates ●● sarcomatous degeneration is estimated to occur in ~20% of cases

●● enchondromatosis: associated with osteochondroma is termed metachondromatosis ●● malignant transformation usually involves a solitary lesion, with cases of multiple CS in enchondromatosis

rarely reported111 ●● Maffucci’s syndrome and Ollier’s disease are also associated with an increased incidence of granulosa cell

tumour of the ovary

●● MRI findings: ●● in childhood, the condition is characterised by linear streaks of cartilage in the long bone metaphyses

(Fig. 8.48a), extending from the growth plate and resulting in bone deformity, including bowing and limb shortening

●● multiple intramedullary (Fig. 8.48b) and/or intracortical chondromas, with similar characteristics to isolated lesions (Figs 8.48b, c)

●● Maffucci’s syndrome: may be identified by the presence of the associated soft-tissue lesion (Figs 8.48d, e) ●● metachondromatosis: is identified by the presence of enchondromas in a patient with multiple

osteochondromas (Figs 8.48f, g)

●● features suggestive of chondrosarcoma over enchondroma include: ●● clinically: male gender, increased age at presentation and pain

●● radiologically: deep endosteal scalloping >2/3 of cortical thickness (but this has less significance in eccentric or subcortical lesions), cortical disruption, periosteal reaction, soft-tissue mass, size >5 cm and a multi-locular appearance on post-contrast T1W images

●● enchondromas commonly affect the tubular bones in the hands and feet, an uncommon site for chondrosarcoma, while the flat bones of the pelvis are a more common location for chondrosarcoma than enchondroma

●● a cut off of 2× the enhancement of normal skeletal muscle in DCE MRI studies resulted in a sensitivity of 100% and a specificity of 67% in differentiating between enchondroma and low-grade chondrosarcoma, with a 93% accuracy in identifying chondrosarcoma115

●● periosteal chondroma: is a rare tumour accounting for <2% of all bone tumours and usually affecting children and young adults in the 3rd and 4th decades

●● they are most commonly located in the metaphysis of the proximal humerus, followed by the femur (medial femoral neck and distal metadiaphysis) and tibia, and are less commonly seen in the small bones of the hands and feet

●● patients typically present with a slowly growing, painful swelling ●● MRI findings:

●● a lobular lesion arising on the cortex but deep to the periosteum, with a mean size of 2.5 cm (range 1-6.5 cm)

●● intermediate SI on T1W (Fig. 8.49a) with hyperintensity on T2W/STIR images (Figs 8.49b, c) and associated focal signal voids due to matrix mineralisation (~70% of cases)

●● marginal periosteal reaction is typical, as is cortical scalloping (Fig. 8.49c) and localised elevation of the cortex at the margin of the lesion

●● the lesion is usually surrounded by a hypointense rim of intact periosteum and cortex, best appreciated on T2W GRE images

●● intramedullary oedema, intramedullary extension and soft-tissue oedema are rare features, while postcontrast imaging reveals thin peripheral and septal enhancement

●● the major differential diagnosis is periosteal chondrosarcoma, which has a larger size (mean 5.3 cm; range 3-14 cm) but no other differentiating features

●● osteochondroma (OC): is also termed cartilage capped exostosis, and accounts for approximately 20-50% of benign bone tumours and nearly 10-15% of all bone tumours

●● OCs: were previously considered developmental lesions rather than true neoplasms, but mutations in the gene encoding exostosin 1 (EXT1) associated with solitary OC suggests that these are neoplastic lesions

●● OC: may also arise following Salter-Harris fractures, surgery and radiotherapy, with a reported prevalence of 6-24% in irradiated patients and the greatest incidence in children under 5 years of age who have received total body irradiation119

●● pathologically: both pedunculated (Figs 8.50a, b) and sessile (Figs 8.50c, d) forms are recognised, the formed having a thin stalk arising from the host bone and typically pointing away from the adjacent joint, while the latter has a broad-based attachment to the underlying bone: ●● the characteristic features are continuity between the medullary cavities of the host bone and the lesion,

and the presence of a variably mineralised/ossified cartilage cap

●● the cartilage cap thickness is typically 1-3 cm in children and only a few millimetres in adults, and it may invaginate into the underlying medullary component of the lesion

●● clinically: they present at any age from 2 to 60 years, but the highest incidence is in the 2nd decade: ●● the metaphyses of long bones are usually affected, especially around the knee (40%), with the commonest

bones affected being the femur (30%), tibia (15-20%) and humerus (10-20%) ●● the commonest flat bones affected are the ilium (5%), scapula (4%) and small bones of the hands and

feet (10%) ●● the vast majority of OCs are asymptomatic, with symptomatic lesions typically affecting younger patients

who present with mechanical problems, such as an enlarging mass, pressure on adjoining structures or rarely fracture of the bony stem (Fig. 8.50e)

●● intra-articular OC are uncommon, and typically result in reduced range of movement or joint clicking120

●● mechanical irritation of overlying soft tissues may result in bursa formation (Figs 8.50f, g), reported in 1.5% of cases of OC and most commonly involving the scapula, hip or shoulder:

● secondary synovial chondromatosis may complicate bursa formation121,122 ●● additional complications include: neurovascular compromise123 due to direct pressure (Fig. 8.50h),

pseudoaneurysm formation most commonly involving the popliteal artery,124,125 and malignant degeneration to peripheral chondrosarcoma

●● lesions arising at the ends of paired bones, such as the tibia and fibula may result in prominent scalloping/ deformity of the adjacent bone (Fig. 8.50i) and complete bony synostosis (Fig. 8.50j)

●● Trevor’s disease126,127 (dysplasia epiphysealis hemimelica; DEH): is a rare developmental condition involving asymmetrical osteochondral overgrowth of an epiphysis or epiphyseal equivalent, resulting in an intra-articular osteochondral mass:

● more common in males and the knee and ankle are most frequently affected, but any joint may be involved

● 3 patterns of disease are recognised: localised (single epiphysis involved, usually in the ankle or hindfoot), classical (involving more than one epiphysis in the same limb), or generalised (involving an entire limb)

● epiphyseal location and the lack of EXT1 and EXT2 gene mutations differentiates Trevor’s disease from OC

●● MRI findings: ●● pedunculated OC: appears as a bony outgrowth from the host bone, attached by a thin stalk, with

continuity of the medullary canal between the two (Fig. 8.50a): ● red marrow SI may be seen within the stalk of a pedunculated OC (Fig. 8.50b), this being of no

clinical relevance and likely related to patient age ● the overlying cartilage cap is isointense to muscle on T1W (Fig. 8.50a), hyperintense on PDW/STIR/

T2W images (Fig. 8.50b), and may appear heterogeneous in younger individuals while undergoing endochondral ossification

● the cartilage cap should measure less than 3 cm in children and is typically 6-8 mm with a maximum of 2 cm in adults

● a cut off of 2 cm cartilage cap thickness in the differentiation of osteochondroma from peripheral chondrosarcoma has a 100% sensitivity and 98% specificity on MRI128

● cap thickness is optimally assessed on axial PDW/T2W images (Figs 8.50b, d) and may show a peripheral thin hypointense rim due to the perichondrium

● the cartilage cap typically shows peripheral/septal enhancement following contrast ●● sessile OC: has a broad-base in continuity with the host bone and an overlying cartilage cap

(Figs 8.50c, d) ●● bursa formation: occurs between the cartilage cap and overlying soft tissues, appearing as a well-defined

or irregular fluid-filled lesion (Figs 8.50f, g): ● rarely, the bursa may contain low SI chondral bodies ● differentiation between bursa formation and hyaline cartilage may be achieved by using pulse

sequences that differentiate free water (bursa) from bound water (hyaline cartilage) such as magnetisation transfer contrast (MTC) or FS 3D SPGR

●● additional findings include denervation changes in adjacent muscle due to nerve compression by the lesion ●● Trevor’s disease: the asymmetric cartilage cap is usually isointense to adjacent physeal cartilage, but may

be slightly hyperintense on T2W sequences: ● cortical and medullary coalescence occurs with maturation (Figs 8.50k, l), and dense foci of

intramedullary calcification are seen as signal voids ● associated local soft tissue and neurovascular complication as with osteochondroma ● articular surface irregularity and altered mechanics predispose to osteoarthritis, and meniscal tears and

valgus deformity in the knee

●● osteochondromatosis: also termed diaphyseal aclasis (DA) or hereditary multiple exostoses (HME) is a rare autosomal dominant condition, with an estimated prevalence of 1:50-100,000 and associated with mutations in the EXT1 and EXT2 genes in 90% of cases

●● most patients are diagnosed by the age of 5 years and all by 12 years of age ●● the exostoses may be larger than the solitary variety and may lead to shortening or deformity of the affected

limbs ●● the metaphyses/metadiaphyses in this condition are also typically widened and dysplastic (Figs 8.51a, b) ●● common sites of involvement: include the scapula and ribs (40%), humerus (50-98%), elbow (35-40%),

wrist (30-60%), hands (20-30%), pelvis (5-15%), hips (30-90%), knees (70-98%), ankles (25-54%) and feet (10-25%)

●● malignant degeneration: in diaphyseal aclasis is approximated at 3-5% and occurs in the cartilage cap, most commonly resulting in secondary low-grade chondrosarcoma, with high-grade/dedifferentiated peripheral chondrosarcoma being a rare development

●● abnormal morphology of the long bone metaphyses, which appear expanded (Figs 8.51a-c) ●● multiple osteochondromas, which may be either sessile (Figs 8.51a-c) or pedunculated ●● ischiofemoral impingement: OC arising from the posteromedial proximal femur with oedema and/or

atrophy of the quadratus femoris muscle (Figs 8.51d, e)

●● chondroblastoma (CB): is a benign chondral tumour that accounts for approximately 1% of all bone neoplasms

●● clinically: CB is more common in men (2.7:1) and presents with joint pain (98%), stiffness (74%), swelling (40%) and a joint effusion (4%),133 since it is typically located in the epiphysis of a long bone and may promote a synovial reaction: ●● 80-90% occur between the ages of 5-25 years (mean age 18 years) and the tumour is rare after the age of

30 years, when flat bones are mostly affected ●● location: 40% arise around the knee, while the proximal femur is the single commonest location, accounting

for 33% of all cases: ●● it is typically located eccentrically in the epiphysis (40%), but with partial closure of the growth plate

usually extends to involve the metaphysis (55%) ●● less than 4% are located purely within the metaphysis

●● epiphyseal equivalents: such as the apophyses and sesamoid bones can also be involved, accounting for locations such as the greater trochanter of the femur (Fig. 8.52a), the greater tuberosity of the humerus, the acromion and patella

●● in the feet: the calcaneus and talus are most commonly involved

●● MRI findings: ●● an epiphyseal or epiphyseal/metaphyseal lesion with well-defined, often lobular margins and a hypo-

intense rim (Figs 8.52b, c) ●● intermediate T1W SI (Fig. 8.52b), hyperintensity on FS PDW/T2W/STIR (Fig. 8.52c) with variable SI

on T2W images, including hypointensity due to abundant immature chondral matrix (Fig. 8.52a), and fluid levels due to secondary ABC change (Fig. 8.52d), demonstrated in 15% of cases

●● associated marrow (Figs 8.52b, c) and soft-tissue (Fig. 8.52c) oedema and reactive joint effusion are almost invariable

●● heterogeneous enhancement is seen following contrast, which also demonstrates enhancement of reactive bone and soft-tissue oedema

●● a thick, solid periosteal reaction occurs in 60% of cases (Fig. 8.52b) and reactive soft-tissue swelling may be observed adjacent to the involved joint

●● occasionally, the lesion can be very large and result in cortical expansion (Figs 8.52e, f ) ●● lesions in the foot commonly result in bony expansion, in addition to the features described above

(Figs 8.52g, h)

●● chondromyxoid fibroma (CMF): is a benign chondral neoplasm, which accounts for less than 0.5% of biopsied primary bone tumours

●● clinically: 75% of cases occur between 10 and 30 years of age (mean age 23-30 years), and most lesions are metaphyseal and eccentric within the medulla (Figs 8.53a, b) resulting in thinning and expansion of the cortex, although lesions may be more centrally located in slim bones, such as ribs, fibulae and small tubular bones

●● intracortical, subperiosteal (Figs 8.53c, d) and juxta-cortical locations are also reported

●● the long bones account for 60% of cases with ~ 25% overall located in the upper third of the tibia and 40% arising in the flat bones (ilium 10%) or small tubular bones of the hands and feet (17%)

●● there is a high local recurrence rate (9%), particularly in younger patients, but only a small risk of malignant transformation (1-2%)

●● MRI findings: ●● the diagnosis is suggested by a proximal tibial metaphyseal location (Figs 8.53a-d), whereas non-tibial

lesions lack characteristic imaging features (Figs 8.53e, f ) ●● the tumour shows hypointense-to-intermediate SI on T1W images (Fig. 8.53e), with internal

hyperintense foci in 37% ●● heterogeneous increased SI on T2W/STIR images (Figs 8.53a-c), with a peripheral intermediate signal

intensity band in 58% ●● peripheral, nodular and diffuse heterogeneous/homogeneous enhancement patterns have been described

following contrast (Fig. 8.53f)135

●● chondrosarcoma (CS): is a malignant cartilage producing tumour and is the second commonest primary malignant bone tumour in the adult skeleton, accounting for 8-17% of all biopsied primary bone tumours and 25% of all biopsied malignant primary bone tumours

●● it is classified as being central when it arises in the medullary cavity, peripheral when it arises in the cap of an OC or periosteal ( juxta-cortical)

●● it may also be classified as primary when arising de novo, or secondary when arising from a pre-existing lesion such as enchondroma/OC

●● pathologically: CS is graded as I-III based on histology, with the majority being low-grade (I): ●● chondral lesions of unknown malignant potential (CLUMP) are atypical cartilaginous tumours, which are

moderately cellular, show mild atypia and myxoid change, and may be regarded as 0.5 grade CS140 ●● histological subtypes include: conventional, clear cell, mesenchymal and dedifferentiated

●● clinically: conventional CS typically presents in the 4th-5th decades of life with pain (almost invariable), swelling in 28% of cases and pathological fracture in 27% of cases

●● the commonest sites of occurrence are the femur, humerus and tibia, accounting for 45% of all cases and involving the metaphysis (49%) followed by the diaphysis (36%): ●● primary epiphyseal CS is rare (16%), while 25% of cases arise from the ilium, 8% from the ribs, 7% from

the fibula and 5% from the scapula ●● the small bones of the hands and feet account for 1-4% of cases

●● MRI findings: ●● the features of conventional central low-grade CS are very similar to those of chondroma, the major

differences being: ● size, with CS tending to be greater than 4 cm (50% >10 cm) (Figs 8.54a, b) ● the presence of deep endosteal scalloping >2/3 the depth of the cortex (Fig. 8.54c)

●● DCE-MRI frequently shows increased relative enhancement and perfusion of low-grade chondral lesions when compared to enchondromas115 but there is a significant overlap with actively enhancing chondromas, particularly in the unfused skeleton and DCE-MRI should be considered complementary to standard MRI in the evaluation of these lesion

●● the tumour has a lobular growth pattern with intermediate T1W SI (Fig. 8.54a) and increased T2W/ STIR SI (Figs 8.54b, c)

●● lobules of tumour may be separated by hypointense fibrovascular septa, which enhance following contrast

●● peripheral enhancement patterns may also be seen (Fig. 8.54d), but the presence and type of enhancement does not clearly differentiate chondroma from low-grade CS

●● matrix calcification is identified in 79% of long bone CS on MRI, appearing as punctate areas of signal void ●● areas of fatty marrow may be trapped within the lesion, appearing hyperintense on T1W and being

seen in 35% of cases (vs 65% of enchondromas), suggesting that the CS had arisen within a pre-existing enchondroma139

●● features that allow accurate differentiation between low-and high-grade appendicular CS include increased tumour length (mean tumour length for high-grade CS is 11.4 cm and 5.5 cm for low-grade CS), bone expansion, medullary oedema, active periostitis and soft-tissue mass (Figs 8.55a-d)140

●● grade III CS appears as a non-specific aggressive destructive lesion, that may show no macroscopic features of chondral origin (Figs 8.55e, f )

●● pelvic CS: most commonly arises in the ilium, with a predilection for the area around the closed triradiate cartilage (Figs 8.56a, b):

● it is typically large at presentation, demonstrating marrow infiltration and a lobular extraosseous mass on either side of the iliac blade

●● CS of the rib/chest wall usually arises at the costo-chondral junction (Figs 8.56c, d)

●● clear cell chondrosarcoma (CCCS): is a rare low-grade central CS accounting for 1-2% of all CS and presenting in the 3rd-5th decades of life, being more common in males

●● the long bones are affected in 85-90% of cases, particularly the proximal femur (68%), the proximal humerus (23%) and around the knee (10-15%), while flat bones are rarely involved

●● unlike conventional CS, the tumour is typically located in the epiphysis, sometimes with metaphyseal extension

●● pathologically: CCCS is characterised by the presence of cells with abundant clear, vacuolated cytoplasm containing glycogen, and the tumour may rarely undergo dedifferentiation

●● MRI findings: ●● a well-defined epiphyseal lesion, which may result in bone expansion, occasionally with a hypointense

sclerotic margin (Fig. 8.57a) ●● low/intermediate T1W SI (Fig. 8.57a), occasionally with hyperintense areas due to intralesional haemorrhage ●● heterogeneous hyperintensity on T2W/STIR images (Fig. 8.57b), rarely with fluid levels and diffuse or

heterogeneous enhancement following contrast (Fig. 8.57c)

●● mineralisation, osseous metaplasia or haemorrhage may all result in heterogeneous SI on T1W and T2W images (Figs 8.57d, e)

●● extraosseous extension is rare, occurring in less than 10% of cases ●● differentiation of smaller lesions from chondroblastoma may be difficult:

● CCCS is suggested by an older age at presentation, lack of associated marrow oedema (Figs 8.57b, e) and T2W hyperintensity

●● mesenchymal CS: is a rare high-grade CS accounting for 2-13% of all CS ●● the average age of presentation is 25 years and 7% of cases may be multicentric ●● sites of involvement include the femur (15-23%), ribs (12-23%), pelvis (10-13%), humerus (4-16%) and, less

commonly, the tibia and fibula ●● most cases arise de novo, but mesenchymal CS may also arise in previous fibrous dysplasia ●● radiographs show aggressive bone destruction with fine, stippled matrix mineralisation in 67% of cases ●● MRI findings:

●● are relatively non-specific, with typical chondroid matrix mineralisation reported in two-thirds of cases ●● intermediate T1W SI (Fig. 8.58a) and intermediate/high SI on T2W/STIR (Fig. 8.58b) images ●● associated soft-tissue extension is common (Figs 8.58a, b) and serpentine flow voids (Fig. 8.58b) may be

seen within the tumour ●● enhancement following contrast is either diffuse or heterogeneous, but does not show the peripheral/septal

pattern of conventional CS

●● periosteal CS: is also termed juxta-cortical CS and accounts for approximately 4% of all CS ●● it most frequently occurs in the 3rd-4th decades of life, presenting as a slowly growing, usually painless mass ●● typical sites of involvement include the long bones, most commonly the posterior aspect of the femoral

diaphysis or distal metaphysis, the proximal humerus, proximal femur and tibia, and the ilium

●● MRI findings: ●● a surface lesion with associated thickening of the underlying cortex, cortical saucerisation and Codman’s triangle ●● the lesion itself has typical features of a well-differentiated chondral tumour, with a lobular growth

pattern, intermediate T1W SI (Fig. 8.59a) and increased T2W/STIR SI (Fig. 8.59b) ●● a peripheral/septal enhancement pattern is also characteristic (Fig. 8.59c) ●● intramedullary extension is rare (~12% of cases), although adjacent medullary oedema may be seen ●● differentiation from periosteal chondroma is made mainly by lesion size, with CS tending to be larger

(3-14 cm), and periosteal chondroma usually measuring less than 2 cm ●● periosteal OS: may have a similar appearance, but typically display a perpendicular periosteal reaction,

while parosteal OS contains extensive osteoid matrix

●● dedifferentiated CS (dd-CS): refers to a situation when a high-grade, non-cartilaginous malignant neoplasm arises in association with a low-grade CS, occurring in approximately 11% of CS

●● the mean age at diagnosis is 66 years and there is an equal male:female ratio ●● sites of occurrence include the femur (55%), pelvis (23%) and humerus (10%) ●● in ~3% of cases, dd-CS may occur in association with peripheral CS or on the surface of the bone, with

similar radiographic appearances to those of central dd-CS other than intramedullary involvement, namely heterogeneous mineralisation, soft-tissue mass and bimorphism148

●● pathologically: the dedifferentiated component is typically OS (70%), fibrosarcoma (24%) or malignant fibrohistiocytic tumour (MFH) (4%) and rarely giant cell tumour (GCT)

●● MRI findings: ●● are typically those of an aggressive destructive lesion with a variety of morphological patterns described ●● evidence of a well-differentiated CS (Figs 8.60a, b) with an associated adjacent high-grade component

(collision tumour), the latter manifest as a region of intermediate SI on T1W and T2W/STIR images (Figs 8.60a, b)

●● following contrast, peripheral/septal enhancement of the chondral component and uniform enhancement of the dedifferentiated component is seen

●● in case of dedifferentiation to predominantly osteoblastic OS, signal void due to osteoblastic matrix mineralisation may be present

●● the presence of chondral-type matrix mineralisation may be the only indication of a pre-existing chondral tumour (Fig. 8.60c)

●● cortical destruction and a soft-tissue mass are evident in 90% and 80% of cases respectively (Figs 8.60a, b) ●● alternatively, in 13% of cases imaging shows features of a non-specific aggressive tumour with no evidence of an

underlying chondral component (Figs 8.60d, e), or in 6% features more suggestive of primary osteosarcoma

●● peripheral CS: is also known as secondary CS and represents the development of CS within the cap of an OC, occurring in ~1-4% of solitary lesions and ~3-9% of patients with diaphyseal aclasis (HME)

●● it accounts for 8% of all CS and is usually solitary and low-grade (67-85% of cases), although dedifferentiation may occur

●● sarcomatous change is more likely to occur in axial lesions, including those located around the pelvis, hips and shoulders, than the peripheries150

●● clinically: it should be suspected with the development of pain or increase in size of a known OC, either solitary or in association with HME: ●● the mean age of development of CS in solitary OC is 50-55 years and in HME is 25-30 years

●● pathologically: malignant change occurs within the cartilage cap (Figs 8.61a-c) and should be suspected if the cap measures in excess of 1.5 cm thickness in an adult: ●● cartilage cap thickness in peripheral CS ranges from 1.5 to 12 cm (mean 5.5-6 cm) ●● rarely, OS may occur in association with OC

●● MRI findings: ●● those of the underlying OC (Figs 8.61a-d)/diaphyseal aclasis ●● cartilage cap thickness is best evaluated on axial T2W images

●● fibrous dysplasia (FD): is a developmental disorder of bone accounting for 7% of benign bone tumours and may be either monostotic (70-85%) or polyostotic (15-30%)

●● clinically: FD is usually painless unless a fracture has occurred, with 75% of cases presenting before the age of 30 years and there is no sex predilection: ●● however, patients with polyostotic disease present earlier (67% by the age of 10 years) and approximately

30-50% of patients with polyostotic disease have café-au-lait spots

●● FD may be associated with a variety of syndromes: ●● McCune-Albright: consists of polyostotic FD (typically unilateral), ipsilateral café-au-lait spots and

endocrine disturbance, most commonly precocious puberty in girls ●● Mazabraud’s: consists of FD (most commonly polyostotic) and soft-tissue myxoma ●● whole body MRI has been advocated as an alternative to radiographs for lesion surveillance in

polyostotic FD154 ●● the commonest sites of monostotic FD are the ribs (28%), proximal femur (23%) and craniofacial bones (20%) ●● polyostotic FD: may range from the involvement of 2 bones to more than 75% of the skeleton and most

commonly affects the femur, tibia and pelvis ●● pathologically: the medullary bone is replaced by a mass of fibroosseous tissue, which may undergo

haemorrhage and secondary ABC change: ●● long bone lesions typically affect the metadiaphyseal region, resulting in endosteal scalloping and well-

defined bone expansion ●● the presence of islands of cartilage, which may mineralise/ossify produces the condition of

fibrocartilaginous dysplasia155 ●● severe skeletal involvement may be associated with deformity and pathological fractures in up to 85% of cases

●● complications: malignant transformation is rare, affecting 0.5-1% of cases but being more common in polyostotic disease: ●● the usual sequelae are OS, fibrosarcoma/MFH and CS ●● a history of previous radiotherapy is noted in 30% of cases

●● MRI findings: ●● affected bones may show mild/moderate expansion, without cortical destruction, periosteal reaction or

soft-tissue extension (Figs 8.62a-c) ●● the lesions tend to be well-defined, commonly with a surrounding hypointense (sclerotic) margin

●● SI characteristics will be determined by the predominant tissue types ●● fibrous/fibroosseous tissue typically has intermediate/low SI on all pulse sequences (Figs 8.62a-c) ●● cystic degeneration appears as low T1W SI (Fig. 8.62d) and hyperintensity on T2W/STIR images

(Fig. 8.62e), while in the presence of haemorrhage increased T1W SI may be seen (Fig. 8.62f), as may fluid levels (Fig. 8.62g)

●● solid areas will show uniform enhancement, whereas cystic areas show rim enhancement ●● additional features in long bone lesions include deformity (Fig. 8.63a) and associated areas of cartilage,

indicating fibrocartilaginous dysplasia (Figs 8.63b, c) ●● flat bones show similar features, with endosteal scalloping, mild expansion and heterogeneous SI

(Figs 8.63d-g)

●● osteofibrous dysplasia (OFD): is a rare lesion that histologically resembles fibrous dysplasia and the stroma of adamantinoma (see later), but having a specific clinical and radiological picture

●● clinically: presentation is from birth to 40 years, with almost 50% occurring under the age of 10, and OFD may regress spontaneously with skeletal maturity

●● pathologically: the tibia is affected in over 90% of cases and in two-thirds of these, the anterior middiaphyseal cortex is involved: ●● multiple lesions may occur in the same bone and the ipsilateral fibula is affected in 20% of cases, with

bilateral involvement occasionally seen ●● MRI findings:

●● the diagnosis is suggested by an anterior intracortical mid-tibial location, with associated anterior tibial bowing commonly present

●● the lesion has intermediate T1W SI (Fig. 8.64a), increased SI on STIR (Fig. 8.64b) and variable T2W SI depending upon the solid (Fig. 8.64c) or cystic (Fig. 8.64d) nature of the lesion

●● lesions are typically loculated, surrounded by a low signal rim and frequently demonstrate medullary involvement (Fig. 8.64a), which is complete in a third of cases

●● diffuse uniform or heterogeneous enhancement occurs following contrast, with peripheral, central or marginal septal patterns of enhancement described, while imaging of the whole bone is required to identify satellite lesions (Fig. 8.64e)

●● fibrous cortical defect (FCD): is commonly seen in childhood, and can almost be regarded as a normal variant, possibly due to a growth disturbance related to subclinical injury at a tendon insertion

●● it is most commonly identified in the distal femoral and proximal tibial metaphyses as an incidental finding on radiographs or MRI of the knee

●● FCD has the same appearance, location and histology as a non-ossifying fibroma (NOF), the lesions differing only in their size, with FCD usually 1-1.5 cm in maximal dimensions, and the lesion typically disappears with time

●● MRI findings: ●● FCD typically appears as a small, lobular intracortical lesion in the metaphysis with low/intermediate SI

on T1W images (Fig. 8.65a) and variable T2W/PDW SI depending upon the solid/cystic components of the lesion (Figs 8.65b-d)

●● enhancement of the solid component is seen following contrast

●● non-ossifying fibroma (NOF): is considered a benign developmental abnormality, with symptoms typically arising when it is large enough to cause a pathological fracture

●● most patients present in the second decade of life, but can present as late as the fifth decade

●● the majority (90%) involve the lower limbs, particularly the tibia and distal femur and multiple lesions are seen in association with neurofibromatosis (5%): ●● Jaffe-Campanacci syndrome:162 consists of multiple (usually unilateral) NOFs (Figs 8.66a, b) with

café-au-lait spots, ocular anomalies, cryptorchism and hypogonadism, but no other stigmata of neurofibromatosis

●● rarely, NOF may produce endocrine substances blocking vitamin D activity, resulting in vitamin D resistant rickets or osteomalacia

●● lesions pass through 4 stages: ●● stage A: small lesion adjacent to the growth plate ●● stage B: increasing size of lesion with lobular borders, extending towards the metaphysis ●● stage C: mineralisation starting in the shaft and extending towards the growth plate ●● stage D: complete calcification of the lesion

●● imaging features are similar to FCD, except that the lesion is larger ●● NOF has intermediate SI on T1W images (Fig. 8.66c) and variable increased SI on STIR (Fig. 8.66d),

commonly with prominent internal hypointensity ●● on T2W images, approximately 80% are hypointense, but with marginal or septal hyperintensity, while

cystic degeneration results in fluid SI (Fig. 8.66e) ●● internal septa may be seen in 95% of cases (Fig. 8.66e) while marginal sclerosis appears as a hypointense

rim (Fig. 8.66c) ●● adjacent marrow oedema may also be demonstrated (Fig. 8.66f) and enhancement of the solid

component is seen following contrast ●● complications include stress fracture163 (Fig. 8.66g), pathological fracture and secondary ABC change,

which may result in the development of fluid levels (Fig. 8.66h)

●● desmoplastic fibroma (DF): is a rare, locally aggressive benign neoplasm, which is considered to be the intraosseous counterpart of soft-tissue fibromatosis

●● it accounts for up to 0.3% of all primary bone tumours, with 70% of cases presenting between 10 and 30 years of age (mean age 21 years)

●● DF usually arises in the metaphyseal/metadiaphyseal regions of long bones (femur, humerus, tibia and radius constitute 56% of cases), the mandible (26%) and ilium (14%), and has rarely been reported in the clavicle and foot164,167

●● approximately two-thirds are central and a third eccentric within the bone, and epiphyseal lesions may also be seen with extraosseous extension reported in ~50% of cases

●● the lesion measures 8 cm in mean longitudinal dimension and is usually greater than 5 cm at presentation ●● it is locally aggressive with bone expansion, but with non-specific SI characteristics, showing

intermediate/low T1W SI (Fig. 8.67a), intermediate/low SI on conventional T2W SE images due to abundant collagen and relative acellularity,170 and heterogeneous increased SI on STIR (Figs 8.67b, c)

●● fibrosarcoma: also termed spindle-cell sarcoma of bone, is the commonest primary malignant tumour of fibrous origin affecting bone and accounts for 5% of primary malignant bone tumours

●● ~25-30% arise in a pre-existing lesion, especially Paget’s disease, post-radiotherapy,172 bone infarction and in relation to dedifferentiated CS

●● rarely, it is associated with fibrous dysplasia (Figs 8.68a-c),173 NOF, chronic osteomyelitis and THR ●● the age range is from 6 to 80 years with the peak incidence in the fourth decade and a slight male pre-

dominance (3:2)

●● the long bone metaphyses are predominantly involved (75% of cases), particularly around the knee, followed by the humerus

●● in 21% of cases, the pelvis, spine or ribs are involved171 and multicentric lesions are also recognised ●● similar clinical and pathological features are seen with fibrosarcoma ●● MRI findings:

●● non-specific aggressive marrow lesion with intermediate SI on T1W and isointense or mildly hyperintense on T2W imaging

●● the diagnosis may be suggested by the presence of a predisposing lesion (Figs 8.68a-c) ●● the tumour is locally destructive and may reach the subarticular surface, mimicking GCT ●● soft-tissue extension is relatively common and ‘skip’ metastases may occur, necessitating imaging of the

whole bone

●● SBC: also termed unicameral bone cyst, is a lesion of unknown aetiology and is not considered truly neoplastic

●● by definition, these cysts are solitary but not always unilocular and most occur between the ages of 5-15 years, with less than 15% reported over the age of 20 years

●● the male to female ratio is 2.5:1 and presentation with pathological fracture is classical, especially with humeral lesions

●● the proximal humerus is by far the commonest site of involvement (>60% of cases), followed by the proximal femur (~30% of cases), while other reported sites tend to affect adults, including the calcaneus and the ilium adjacent to the SIJ

●● pathologically: appendicular SBC originates in the proximal metaphyses of the humerus or femur adjacent to the physeal plate and progresses into the diaphysis with skeletal growth, eventually reaching the junction of the middle and distal thirds of the shaft, by which time it has usually healed: ●● occasionally, the cyst adheres to the growth plate and extension into the epiphysis/apophysis is reported in

2% of lesions (Figs 8.69a, b) ●● SBC usually lies centrally in the shaft, expanding the bone symmetrically and thinning the cortex, and is

typically 6-8 cm in size ●● fracture may result in a fragment of cortex penetrating the cyst lining, resulting in the ‘fallen fragment’

sign, reported in only 5% of cases radiologically ●● the ‘rising bubble’ sign involves a locule of gas or vacuum phenomenon rising to the non-dependent aspect

of a SBC containing a pathological fracture, seen as T1 and T2 low SI, with blooming artefact on gradient echo sequences177

●● MRI findings: ●● the fluid content of the lesion is manifest by homogeneous low/intermediate SI on T1W

images (Fig. 8.69c), although mild hyperintensity due to a high protein content may be seen (Fig. 8.69a)

●● marked hyperintensity on T2W/STIR images is typical (Fig. 8.69b) and rim enhancement is seen following contrast (Fig. 8.69d)

●● these appearances are altered by the presence of fracture, in which case haemorrhage may result in the presence of fluid-fluid levels (Fig. 8.69e) and pericystic oedema (Fig. 8.69f)

●● occasionally, a ‘fallen fragment’ may be identified (Fig. 8.69f)

●● primary ABC: accounts for 70% of ABCs, 1-2% of all primary bone lesions and usually presents in the second decade, with 70-80% occurring between 5 and 20 years of age

●● recent cytogenetic studies indicate that primary ABC represents a true neoplasm, rather than a benign reactive lesion

●● secondary ABC change: represents 30% of ABCs and can develop in a variety of preceding benign or malignant lesions, including NOF, chondroblastoma, giant cell tumour, fibrous dysplasia, OB and OS

●● ABC can involve many sites, but the long bones are commonest (over 50% of cases), mainly the femur and tibia, with only 7% occurring in the pelvis181

●● long bone lesions typically occur eccentrically within the metaphysis (Figs 8.70a-c), resulting in bone expansion, which can be dramatic, and 20% of lesions are diaphyseal

●● intracortical (Fig. 8.70e) or subperiosteal ABC (Fig. 8.70f)182 is also recognised and accounts for ~15% of all ABCs: ●● they most commonly arise from the forearm bones, femur and tibia and are typically diaphyseal or

metadiaphyseal in location, classically showing erosion of the outer cortex ●● involvement of flat bones is commonest in the pelvis, followed by the scapula ●● pathologically: ABC classically consists of multiple blood filled spaces separated by thin septa:

diffuse enhancement following contrast (Figs 8.71a, b)

●● MRI findings: ●● the typical features are of an eccentric, metaphyseal expansile lesion, with a well-defined hypointense rim,

due to a thin ‘egg-shell’ of expanded cortex or periosteum (Figs 8.70a-c) ●● periosteal reaction, in the form of a Codman’s triangle may be seen at the margins of the lesion

(Fig. 8.70d) ●● the lesion is of heterogeneous intermediate/increased SI on T1W images (Fig. 8.70a) with heterogeneous

increased SI on PDW/T2W/STIR images (Figs 8.70b, c) ●● the classical feature is the presence of multiple fluid levels, optimally appreciated on sagittal or axial PDW/

T2W images (Figs 8.70c, e, f ): ● the vast majority of lesions showing >2/3 fluid levels will be ABCs, and lesions composed entirely of

fluid levels are benign and need not be biopsied prior to treatment, provided that there are no associated atypical features85,187

● semi-automatic MRI techniques are available for measurement of fluid volume within a lesion188 ● the significance of T1W SE images (Fig. 8.70g) in the assessment of fluid levels has also been

investigated, with reduced T1W SI in the superior component compared to the inferior component being significantly associated with a benign lesion189

●● thin, hypointense internal septa are a common feature, and these may show enhancement following contrast (Fig. 8.70h)

features is reported as 77.8% and 66.7%, respectively178

●● GCT: is an aggressive benign neoplasm accounting for approximately 4-9.5% of primary bone tumours and 18-23% of benign neoplasms

●● however, <10% of GCTs show malignant change, being either primary or secondary (typically following radiotherapy to the primary tumour) and benign lesions may rarely metastasise to the lungs

●● multi-focal, metachronous GCT occurs in 1% of patients, in which case hyperparathyroidism must be excluded, and GCT can also complicate Paget’s disease of bone

●● approximately 80% occur between 20 and 50 years of age, only 1-3% in children and 9-13% in the over 50s, with a male to female ratio of 2:3

●● 84-99% of lesions extend to within 1 cm of subarticular bone, or adjacent to a fused apophysis, being eccentrically located in 42-93% of cases (Figs 8.72a-c)

●● the distal femur (23-30%), proximal tibia (20-25%), distal radius (10-12%) (Figs 8.72d, e) and proximal humerus (4-8%) are the commonest appendicular sites

●● rarer sites include the proximal femur (4%), the distal tibia (2-5%) (Fig. 8.72f), the proximal fibula (3-4%), the innominate bone (3%), the hand/wrist (1-5%) and the foot (1-2%)

●● MRI findings: ●● GCT is classically a subarticular, eccentric lesion with a well-defined, non-sclerotic margin, usually

measuring 5-7 cm in size at presentation ●● poorly-defined margins, seen in 10-20% of cases, suggest a more aggressive growth pattern ●● involvement of the subchondral (Figs 8.72c-f) or apophyseal bone is classical, although lesions arising in

the immature skeleton involve the metaphysis adjacent to the growth plate ●● cortical expansion is a common feature, with cortical destruction and extraosseous extension occurring in

33-44% of cases (Figs 8.72e, f ) ●● GCT usually has intermediate SI on T1W images (Figs 8.72a, d, f ) and shows heterogeneous

hyperintensity on STIR (Fig. 8.72e) ●● areas of hyperintensity on T1W/PDW images indicate the presence of subacute haemorrhage, whereas

areas of low SI indicate chronic haemorrhage (Fig. 8.72c) ●● profound hypointensity on T2W images (Fig. 8.72b), particularly T2W GRE, in solid areas of the

tumour is seen in the majority of cases, being due to the deposition of haemosiderin from chronic recurrent haemorrhage and the collagen content of fibrous components

●● marrow oedema is also relatively common (Fig. 8.72a), while fluid-fluid levels indicate the presence of secondary ABC change (Fig. 8.72g), which is reported in approximately 14-53% of cases

●● solid areas enhance uniformly following contrast, whereas cystic areas show peripheral and septal enhancement (Fig. 8.72h), and pathological fracture is not uncommon, particularly with distal femoral lesions (Fig. 8.72i)

●● malignant GCT has no characteristic distinguishing features

●● both solitary and multiple haemangiomas and lymphangiomas occur in bone and may be regarded as congenital vascular malformations

●● unlike the majority of primary bone tumours, intraosseous haemangiomas are twice as common in women

●● however, many present as isolated bone lesions and are therefore included in the differential diagnosis of a bone tumour, particularly in the case of expansile lesions

●● pathologically: haemangiomas are classified histologically as capillary, cavernous, arteriovenous or venous: ●● cavernous and capillary subtypes are most common, but the matrix in all subtypes includes vessels, fat,

smooth muscle, fibrous tissue and clotted blood ●● osseous capillary haemangiomas most commonly affect the vertebral body, whereas osseous cavernous

haemangiomas most commonly affect the skull vault ●● involvement of the long bones is uncommon, affecting the medullary canal of the metaphysis or diaphysis,

with the epiphysis most commonly involved in multi-focal haemangiomatosis ●● the femur, tibia or humerus are most commonly involved, with approximately 3/4 of all extra-axial lesions

involving the lower extremity ●● a characteristic feature of haemangioma is the presence of trabecular thickening resulting in a honeycomb,

‘Irish lace’ or spiculated appearance, which may be identified on radiographs and CT ●● intralesional calcification is less common in intraosseous haemangiomas than in their soft-tissue

counterparts, and purely lytic lesions have also been described ●● MRI findings:

●● trabecular thickening is commonly in a vertical orientation along the bone, appearing as multiple, linear, hypointense striations (Fig. 8.73a) and hypointense dots on axial images (Fig. 8.73b)

●● rounded or curvilinear intraosseous vascular channels are also a characteristic feature (Figs 8.73c, d)

●● in the presence of slow-flow lesions, these channels are of low-to-intermediate T1W SI and increased T2W SI (Figs 8.73c, d)

●● occasionally, the lesion may manifest as a poorly-defined area of marrow oedema-like SI ●● high-flow osseous arteriovenous malformations manifest as low SI channels on all pulse sequences

(Figs 8.73e-g)

●● periosteal reaction, bone marrow and soft-tissue oedema are variable findings ●● rarely, osseous haemangiomas are confined to the subperiosteum or cortex,196 usually involving the long

bones of the lower extremities, and most commonly located in the anterior tibial diaphysis: ● imaging findings include lucency, adjacent cortical thickening or occasionally cortical erosion, a ‘wire

netting’ trabecular pattern and hyperintensity on T1W images ● marrow involvement is typically absent ● the imaging appearances may be similar to those of an OO

●● cystic angiomatosis: is defined as a diffuse, extensive haemangiomatous and/or lymphangiomatous infiltration of multiple tissues including bone, muscle, viscera (in particular the lungs, liver and spleen) and subcutaneous fat

●● osseous lesions appear as multiple lucencies with a soap bubble or honeycomb appearance, usually orientated along the long axis of the bone

●● it is a condition of the young, with 50% presenting before 20 years of age ●● bone lesions occur in 75% of cases of lymphangiomatosis, and although isolated skeletal involvement is

recognised, associated soft tissue and visceral involvement occurs in 60-70% ●● haemangiomatosis limited to the skeleton carries a better prognosis and is seen in 30-40% of cases ●● sites of involvement include the femur, ribs, spine, pelvis, humerus, scapula, other long bones and the clavicle,

with central skeletal lesions more common than peripheral involvement ●● the joints are not directly involved and the condition may be limited to a single extremity, resulting in

gigantism ●● bisphosphonate treatment: can limit disease progression and increase bone density,199 but may result in

osteosclerotic conversion of the lesions with increased bone fragility198 ●● MRI findings:

●● similar to those seen with solitary haemangioma but more extensive ●● MRI may demonstrate associated soft-tissue extension (Figs 8.74a, b)

●● massive osteolysis: is also known as Gorham’s disease or vanishing bone disease and represents a rare, noninheritable disorder, which occurs at any age, but predominates in children and young adults

●● pathologically: it is identical to cystic angiomatosis and characterised by a non-malignant proliferation of vascular or lymphatic structures of bone resulting in progressive bony destruction, often with extension into the surrounding soft tissues

●● it is typically monostotic and most commonly affects the shoulder region, mandible and pelvis, although any bone may be affected

●● progressive resorption of a single bone occurs, but paired bones, several contiguous ribs and segments of the spine may also been affected

●● spontaneous arrest and resolution is rarely reported ●● MRI findings:

●● similar to other haemangiomatous conditions, with destructive lesions of the metaphysis and diaphysis of long bones (Figs 8.75a, b) and the absence of any major soft-tissue mass being a notable features

●● there is usually no associated periosteal reaction, and progressive contiguous bony destruction usually occurs without ‘skip’ lesions

●● malignant vascular tumours: arising in bone include epithelioid haemangioendothelioma and angiosarcoma

●● epithelioid haemangioma: is a benign lesion but shows clinical and histological overlap with these malignant vascular tumours, and may demonstrate multi-focal lymphatic involvement/metastases: ●● skeletal lesions may be solitary or multi-focal (25%) (Figs 8.76a-c), and although frequently presenting

as painful, well-defined lytic lesions with no cortical destruction, they can cause osseous destruction and expansion with extraosseous extension

●● epithelioid haemangioendothelioma: is multi-focal in approximately 40% of cases, but has a propensity to be limited to a single anatomic region: ●● individual lesions are lytic with a small extraosseous mass identified in 40% of cases

●● angiosarcoma: represents a high-grade vascular neoplasm, which may also be unifocal or multi-focal: ●● the mean age of presentation is in the 3rd-4th decades and skeletal involvement is commonest in the long

bones (60% of cases), usually the tibia, femur, humerus and pelvis ●● angiosarcoma has a recognised association with previous radiotherapy and lymphoedema

●● MRI findings: ●● the imaging features are non-specific, being those of an intermediate to markedly aggressive, lytic

destructive process (Figs 8.77a, b) ●● high-flow vascular channels may result in the presence of serpiginous flow voids ●● fluid levels are also reported

●● Ewing sarcoma (ES) and primitive neuroectodermal tumour (PNET): are related entities differentiated by immunohistochemical techniques, but sharing mutations involving chromosomes 11 and 22: ●● PNET of the chest wall is referred to as the Askin tumour

●● ES: is a rare, highly malignant primary bone neoplasm accounting for approximately 5% of biopsied primary tumours, and exceeded in prevalence only by OS in children and adolescents: ●● together OS and ES represent 90% of primary malignant bone tumours in children

●● clinically: 75% of patients are <20 years at presentation, 95% 4-25 years and 95% occur in Caucasians, with males more frequently affected: ●● presentation is with localised pain and swelling, and the presence of systemic symptoms including pyrexia

and raised erythrocyte sedimentation rate (ESR) simulate infection and signify disseminated disease and a poor prognosis

●● pathologically: a single bone is usually involved, but multiple lesions occur at presentation in 10% of cases, more commonly later in the disease: ●● most lesions show extensive involvement of the metadiaphysis (59%) or the diaphyseal region (35%) of a

with a better prognosis210

●● the bones most commonly affected are the femur and humerus (together 31% of cases), the pelvic bones (21% of cases, most commonly the ilium), and ribs (6.5-8% of cases)

●● the distal appendicular skeleton is involved in 27% of cases ●● MRI findings:

●● in long bones: extensive metadiaphyseal/diaphyseal marrow infiltration is typical (Figs 8.78a, b): ● the SI characteristics are non-specific, with intermediate T1W (Fig. 8.78a) and intermediate/high

PDW/T2W/STIR SI (Figs 8.78b, c)

● enhancement of solid tumour occurs following contrast, and post-contrast imaging can prevent overestimation of tumour size, since areas of cystic necrosis are non-enhancing but show fluid SI on T2W images (Fig. 8.78b)

● a moderate/large, soft-tissue extension is almost always present (Figs 8.78b, c), which is commonly circumferential and may be limited at its margins by a Codman’s triangle

● typical patterns of periosteal reaction include vertical and multi-laminated, which may be evident on MRI ● irregular cortical thickening (Fig. 8.78c) with mild bone expansion may occur, while erosion of the

outer cortex by subperiosteal tumour results in cortical saucerisation (Fig. 8.78d) ● ‘skip’ metastases are a recognised finding, requiring imaging of the whole bone ● whole body MRI, with or without diffusion sequences may be used as an alternative to, and is possibly

more sensitive than, whole body scintigraphy for staging10,211 ●● an unusual presentation is of a mainly extraosseous mass with a relatively small intraosseous component,

usually seen in adults (Figs 8.78e, f )212 ●● in flat bones: ES is characterised by the presence of a large soft-tissue mass on either side of the bone, with

associated aggressive bone destruction (Figs 8.79a-c): ● bone metastases (distant metastases and ‘skip’ lesions) may be seen at the time of presentation (Fig. 8.79c) ● occasionally, ES demonstrates a mixed or mainly sclerotic appearance, especially in the flat bones (Fig. 8.79d)

●● periosteal Ewing sarcoma (PES): is an extremely rare tumour, which most commonly presents in adolescent males as a subcutaneous mass

●● lesions are lytic on plain radiography, with subperiosteal cortical erosion and a Codman’s triangle ●● the commonest reported sites are the proximal humerus and proximal femur, mainly in a diaphyseal/

metadiaphyseal location ●● MRI findings:

●● a soft-tissue mass arising on the surface of the bone with no cortical penetration or intramedullary extension214 (Figs 8.80a, b)

●● the lesion has no characteristic SI changes, and shows either uniform or heterogeneous contrast enhancement

●● the lack of matrix mineralisation differentiates PES from parosteal OS and periosteal CS, while the absence of a perpendicular periosteal reaction is a helpful discriminator from periosteal OS

●● PBL: the diagnosis of PBL depends upon involvement of a single site in bone with no evidence of disease elsewhere in the body for at least 6 months after diagnosis, excluding regional lymph node metastasis

●● PBL is the rarest primary intraosseous malignancy, accounting for approximately 3% of malignant bone tumours

●● pathologically: the majority are B-cell non-Hodgkin’s lymphoma (NHL) with primary Hodgkin’s disease of bone being extremely rare,220 with PBL occurring in <1% of Hodgkin’s disease and accounting for ~6% of PBL cases

●● clinically: the age at presentation is from the 2nd-8th decades, with a mean age of approximately 50 years: ●● a slightly biphasic age distribution is recognised, showing peaks around 20 and 50 years

●● the metadiaphyses of long bones are most commonly involved, particularly the femur (25%), tibia and humerus: ●● a primary lesion centred on the epiphysis is extremely rare, with only a few reported cases221

●● synovitis can occur in an adjacent joint, most often the knee and lesions can cross a joint space to involve an opposing bone

●● imaging features are very similar to ES, with poorly-defined extensive infiltration of the metadiaphyseal region of a long bone (Figs 8.81a, b) and typically a large extraosseous soft-tissue mass (Fig. 8.81c), but rarely, PBL may be confined to the cortex or periosteum

●● areas of bone involvement are hypointense on T1W and show variable heterogeneous SI on T2W SE sequences, sometimes resulting in a ‘mosaic’ SI pattern

●● heterogeneous/low signal intensity areas may relate to a high content of fibrous tissue ●● the majority of lesions have a periosseous soft-tissue cuff or more significant soft-tissue component ●● solid tumour enhances following contrast, while areas of necrosis demonstrate fluid characteristics and

occasionally fluid levels ●● characteristic features: include a relative lack of bone destruction (Figs 8.81a-c), the presence of

sequestra, seen in 11-16% of cases and appearing as focal areas of signal void, and regional lymph node enlargement (Fig. 8.81d)

●● intraosseous lipoma: is an uncommon intramedullary tumour, although the commonest lipomatous tumour of bone

●● clinically: it affects patients from 5 to 85 years, but most commonly presents in the 4th-5th decades of life: ●● pain is reported in 66% of cases, with the remainder commonly presenting as incidental findings

●● pathologically: medullary bone is replaced by mature fat, resulting in expansion, sometimes with endosteal scalloping and trabeculation: ●● tumours range in size from 2 to 13 cm (mean 5-6 cm) ●● rarely lesions may be multiple, a condition termed intraosseous lipomatosis, possibly associated with

hyperlipoproteinaemia ●● tumours may be divided into 3 stages:

●● stage 1: lesions containing viable fat which cause trabecular resorption, without necrosis (Figs 8.82a, b) ●● stage 2: lesions having viable fat and fat necrosis, with regions of dystrophic calcification (Fig. 8.82c) ●● stage 3: lesions demonstrating involutional changes, with extensive fat necrosis, cyst formation,

calcification and reactive new bone formation (Figs 8.82d-g)

●● common sites of involvement are the intertrochanteric region of the femur (34%), calcaneus (8%), ilium (8%; most commonly adjacent to the SIJ), tibia (13%), fibula (12%), humerus (5%) and ribs (5%)

●● long bone lesions are typically metaphyseal and intramedullary, although intracortical and surface lesions are occasionally seen227,228

●● malignant transformation of an intraosseous lipoma is extremely rare, and may be mistaken for malignant transformation within a bone infarct229

●● MRI findings: ●● depend on the stage of the lesion, but typically, a well-defined lesion with a thin hypointense

(sclerotic) margin and internal trabeculation, although trabecular resorption may be evident (Figs 8.82a-c)

●● expansile remodelling of the bone may be present in stages 2 and 3, helping to differentiate an intra-osseous lipoma from a bone infarct (Figs 8.82d-g)

●● the lesion has a predominantly fatty matrix, appearing hyperintense on T1W/PDW/T2W FSE images (Figs 8.82b-d, f ) and hypointense on FS PDW/T2W FSE/STIR (Figs 8.82a, g) and T2W GRE images

●● cystic areas demonstrate fluid SI characteristics (Figs 8.82d, e), while the presence of calcification/ sclerosis/fibrosis results in areas of signal void (Figs 8.82c, f, g)

●● intracortical lesions appear as areas of fatty cortical expansion (Figs 8.82h, i)

●● parosteal lipoma: is a rare benign tumour arising from the mesenchymal cells of the periosteum, representing up to 15% of all osseous lipomas and 0.45% of all bone tumours

●● clinically: it presents in the 40-60 years age range as a slowly growing, painless mass: ●● proximal forearm lesions may be associated with compression neuropathy of the posterior interosseous

nerve, and sciatic, median and ulnar nerve compression has also been reported ●● pathologically: it consists of mature fatty tissue adherent to the underlying periosteum:

●● cartilage, osseous metaplasia and bony excrescences or cortical thickening are commonly seen adjacent to the lesion

●● subtypes of parosteal lipoma exist, based on the presence of chondroid matrix and endochondral ossification:230

● no ossification or chondroid matrix within the lipoma, which rests on the cortex ● pedunculated or sessile exostosis mimic, comprising a narrow osseous stalk with lipomatous cap ● patchy chondro-osseous tissue within the lipoma

●● the commonest sites of involvement are the proximal thigh adjacent to the femur, and the forearm near the proximal radius, although multiple other sites have been reported

●● MRI findings: ●● a juxta-cortical fatty mass with increased SI on T1W and T2W FSE images (Fig. 8.83a) and reduced SI

on STIR/T2W FSE FS images (Fig. 8.83b) ●● hypointense fibrovascular septa are present within the lesion, possibly producing a lobular appearance ●● areas of intermediate T1W SI and increased T2W SI may be seen, corresponding to cartilaginous

components ●● abnormal underlying bone is reported in 70% of cases and osseous reaction in 50% of cases:

● osseous changes include bowing of the bone (usually in the immature skeleton), cortical erosion or surface bone production (Fig. 8.83a), which does not show continuity with the underlying medullary cavity

●● associated features include denervation atrophy of adjacent muscles

●● LSMFT: is a rare benign tumour, which may be a variant of fibrous dysplasia ●● clinically: most are discovered incidentally or are associated with vague pain (48%), and rarely present with

pathological fracture (10%)

●● pathologically: it is a benign fibroosseous lesion composed of lipoma, fibroxanthoma, myxoma, myxofibroma, fibrous dysplasia-like areas, cyst formation, fat necrosis, ischaemic ossification and, occasionally, cartilage: ●● the lesion may be the result of degenerative changes including myxoid transformation, fat necrosis,

reactive bone change and calcification in a pre-existing fibrous dysplasia or intraosseous lipoma232 ●● ~85% affect the femur, with 90% of these arising in the intertrochanteric region ●● malignant change has been identified histologically in ~10% of cases ●● MRI findings:

●● a well-defined oval lesion, which may cause mild bone expansion ●● SI reflects the contents, with areas of low T1W SI (Fig. 8.84a) and increased T2W/STIR SI due to the

myxoid component (Fig. 8.84b) ●● frank fat SI is rarely seen, while foci of signal void may indicate matrix mineralisation (Figs 8.84a, b) ●● many lesions may be difficult to distinguish from fibrous dysplasia

●● intraosseous hibernoma: is a rare benign tumour composed of brown fat ●● most cases are picked up as incidental sclerotic lesions in middle-aged and elderly patients, frequently affecting

the axial skeleton ●● MRI findings:

●● heterogeneous T1W hyperintensity, but lower SI than subcutaneous fat, with variably hyperintense or rarely hypointense SI on T2W and STIR sequences, and vessels or low signal bands often visible within the mass

●● heterogeneous post-contrast enhancement

●● LCH: is now considered to represent a malignant bone tumour, accounting for ~1% of biopsied primary bone lesions

●● it is an extremely heterogeneous disorder, which embraces Letterer-Siwe disease, Hand-Schüller-Christian disease and eosinophilic granuloma (EG), the latter term used to describe disease limited to a single or a few bones, with no associated extraskeletal involvement, and thus presenting as a bone tumour

●● EG: accounts for ~70% of all LCH cases, with ~80% presenting before the age of 10 years, although the disease is also seen in adolescents, young adults and occasionally as late as 60 years

●● clinically: presentation is usually with pain and local tenderness, the ESR being either normal (<50% of cases) or showing a moderate elevation (<60 mm/h), in which case the condition mimics low-grade infection

●● >50% of cases involve the skull, spine, pelvis, ribs and mandible ●● in the long bones (25-35% of cases of monostotic disease), the femur, tibia and humerus are typically involved

and within the long bones, diaphyseal involvement is commonest (58%), followed by metaphyseal (28%) and metadiaphyseal (12%), while ~2% of lesions involved the epiphysis

●● long and flat bones are affected equally in children, but flat bone involvement is more frequent in adults over 20 years, most commonly the ribs

●● lesions of the hands and feet are rare, and multiple lesions are demonstrated in ~10% of cases at presentation ●● MRI findings:

●● long bone and flat bone lesions present as mild/moderately aggressive focal lesions with intermediate T1W SI (Fig. 8.85a) and increased SI on T2W/STIR (Fig. 8.85b) images, with heterogeneous post-contrast enhancement (Fig. 8.85c)

●● endosteal scalloping (Fig. 8.85a) with a ‘budding’ subperiosteal appearance and/or mild bone expansion may be seen

●● surrounding marrow oedema, periosseous oedema and periosteal reaction are common (Figs 8.85b, c) and indicative of active lesions, whereas absence of surrounding SI abnormality suggests quiescent/healed disease

●● whole body MRI: is more sensitive than plain radiography and bone scintigraphy in the detection of skeletal lesions, and will also identify extraskeletal pathology in multi-system disease239

●● adamantinoma: is a rare low-grade malignant tumour accounting for 0.1-0.5% of all malignant bone tumours

●● clinically: most cases occur between 10 and 50 years with an average age at presentation of 35 years and is slightly more common in males, patients usually having local pain and tenderness of several months to several years duration: ●● risk factors for aggressive behaviour of the lesion include male sex, young age at presentation, short

duration of symptoms, pain at initial presentation and local recurrence ●● 85%–90% occur in the tibia, mostly in the mid-shaft (Figs 8.86a-d) but almost as commonly towards either

metaphysis (Fig. 8.86e) ●● synchronous involvement of the tibia and fibula is reported in 10-50% of cases with other bones rarely

affected, and multi-focal lesions in the same long bone are occasionally seen ●● initially, the tumour is eccentric but eventually involves the whole depth of the shaft ●● pathologically: differentiation is made between classical adamantinoma and OFD-like adamantinoma, which

is of clinical importance since the former is more likely to metastasise, usually to the lungs and lymph nodes and less commonly to the bones: ●● OFD, OFD-like adamantinoma (Figs 8.86a, b) and adamantinoma (Figs 8.86c-g) have similar imaging

appearances, but increased length of lesion (average lesion length is 13.2 cm for adamantinoma, and 6.1 cm and 6.5 cm respectively for OFD and OFD-like adamantinoma), complete medullary involvement and a moth-eaten border are more suggestive of adamantinoma156

●● MRI findings: ●● eccentric involvement of the diaphysis of the tibia is classical, the majority being predominantly

intracortical (Figs 8.86a, b, f ) and showing well-defined cortical destruction ●● the lesion usually has a sclerotic, lobular margin and internal ossification (Figs 8.86c, d) or septa may be

identified ●● a multilocular appearance and satellite lesions are useful diagnostic features ●● extension into the marrow cavity is seen in 60% of cases (Figs 8.86d, e), extraosseous extension and

multi-focal lesions (Fig. 8.86e) in 15-27% of cases, while rarer findings include anterior tibial bowing and bony expansion

●● there are no specific SI characteristics, with the MR appearances being somewhat variable, depending upon the presence of cystic components

●● intense enhancement is seen following contrast (Fig. 8.86g) ●● MRI is unable to clearly differentiate between the 2 histological subtypes

Bone Metastasis ●● bone metastases: are common and often multiple ●● however, ~9% of carcinoma bone metastases are solitary, making a solitary metastasis much more common

than a primary malignant bone tumour ●● bone metastases: are commonest from carcinoma of the breast, bronchus, prostate, kidney and thyroid, and

the commonest sites are those containing red bone marrow, such that the axial skeleton is affected more commonly than the appendicular skeleton in adults

●● therefore, bone metastases commonly involve the vertebrae, pelvis, proximal femora and humeri, skull and ribs, while peripheral metastases are rare with 50% of these being from bronchus

●● whole body MRI: using non-contrast coronal T1W and STIR sequences is highly accurate in the detection of skeletal metastases,243 but can be supplemented with additional MRI techniques:244

●● chemical shift imaging: utilises the difference between the signal of normal fat-containing bone marrow and that of lesional marrow replacement on opposed phase imaging, and whilst useful in evaluating malignant versus benign lesions, there is a certain amount of overlap between pathologies

●● DWI:245,246 relies upon variations in diffusibility of tightly packed tumour cells compared to that of oedema and necrosis, and in the field of musculoskeletal imaging has been of most use in differentiation between benign osteoporotic/traumatic vertebral fractures and metastatic vertebral collapse

●● MRI findings: ●● most metastases are lytic and located in the medulla, showing intermediate SI on T1W/PDW images

(Figs 8.87a, b), with intermediate/increased SI on T2W images and hyperintensity on FS T2W FSE/ STIR images (Fig. 8.87c)

●● the identification of a hyperintense ‘halo’ around a lesion is a highly specific feature of metastasis on T2W images

●● sclerotic metastases, commonly arising from prostate or breast, show reduced SI on both T1W and T2W images (Fig. 8.87d)

●● vascular metastases, such as those arising from renal carcinoma, may show serpentine flow voids247 (Fig. 8.87e)

●● some metastases may be subarticular in location (particularly renal) (Fig. 8.87e), or predominantly intracortical, commonly involving the femur and arising from the bronchus (Fig. 8.87f)

●● additional, non-specific features include pathological fracture and soft-tissue extension (Fig. 8.87g)

●● following chemotherapy: successfully treated malignant lesions may display a rim of fat with or without reduced contrast enhancement, indicating effective treatment:

● however, necrotic metastases may remain unchanged in morphology and SI after treatment, making it difficult to evaluate therapeutic response

●● in late foetal life and infancy, the entire bone marrow is utilised for red blood cell (RBC) formation, supplemented by extramedullary erythropoiesis in the liver and spleen

●● as a result, the diaphyseal cortex of the third trimester foetus is relatively thick, with only a narrow intramedullary canal, resulting in a diffuse hypointense SI of the skeleton

●● in the first weeks of life, the marrow space becomes more evident, and is filled with haematopoietic marrow

●● as the child becomes older and RBC lifespan increases, erythropoiesis is withdrawn from the liver and spleen, then gradually centripetally from the peripheries and diaphysis to metaphyses of the long bones, so that by the age of 18-20 years active bone marrow is confined to the axial skeleton, the flat bones and the proximal ends of the femora and humeri

●● conversion to fatty marrow occurs first in the epiphyses, within 6 months of the radiological appearance of the secondary centre of ossification

●● the process of withdrawal will not occur if there is a need for extraerythropoiesis, and the process reverses in the presence of increased RBC destruction, resulting in marrow reconversion in the opposite direction to that of fatty marrow conversion, with the epiphyses the last to reconvert

●● normal adult marrow contains both fat and water: ●● yellow marrow: 80% fat and 15% water ●● red marrow: 40% fat and 40% water

●● MRI findings: ●● on T1W SE/PDW and T2W FSE images, yellow marrow appears hyperintense (isointense to

subcutaneous fat) and red marrow appears mildly hypointense to fat but hyperintense to skeletal muscle (Fig. 8.88a)

●● on FS PDW/T2W FSE and STIR images, yellow marrow appears hypointense and red marrow demonstrates mild hyperintensity (Fig. 8.88b)

●● on GRE images, the marrow appears generally hypointense, with red marrow showing marked hypointensity (Fig. 8.88c):

● marrow hypointensity is also a function of magnetic field heterogeneity created by trabecular bone, which is most marked in the vertebrae, pelvic bones and proximal ends of the long bones

●● following contrast, SI changes in normal marrow are not appreciable on T1W SE images ●● within the long bones, prominent residual red marrow is present in:

● the medial metaphysis of the proximal humerus (Fig. 8.88d) ● the medial neck and metaphysis of the proximal femur (Fig. 8.88e) ● the posterior aspect of the distal femoral metaphysis (Figs 8.88a-c) ● the posterior aspect of the proximal tibial metaphysis (Fig. 8.88f)

●● chronic haemolytic anaemia: will result in marrow reconversion, which affects the appearance of the bone marrow on MRI

●● thalassaemia:252,253 is an inherited defect of haemoglobin A synthesis with inadequate manufacture of α or β chains: ●● β-thalassaemia is prevalent in Europe and the Near East, while α-thalassaemia is encountered in the Far East ●● thalassaemia is transmitted by an autosomal dominant gene and exists in two forms, homozygous

(thalassaemia major) and heterozygous (thalassaemia minor and thalassaemia minima), with radiological changes being typically limited to thalassaemia major

●● sickle cell disease (SCD):251,252,254 occurs due to abnormal red cell formation: ●● the full clinical and radiological picture occurs in the homozygous sickle cell subject (Hb S-S) and skeletal

changes are due to a combination of: ● chronic anaemia resulting in marrow reconversion, and vaso-occlusive disease, resulting in marrow

infarction ●● in children: bone infarction occurs most frequently in the hands and feet resulting in destructive lesions

with associated periostitis and soft-tissue swelling: ● the resulting dactylitis is termed ‘hand-foot syndrome’ and typically occurs before the age of 4 years

and rarely after the age of 7 years, due to replacement of red marrow by fibrous tissue in these bones ● asymmetrical shortening of tubular bones (e.g. hands or feet) is a common sequel a to childhood sickling crises

●● in adolescents and adults: infarction occurs more in the metaphyses and epiphyses: ● diaphyseal infarctions are also common, causing localised metadiaphyseal osteolysis and periosteal

reaction ● infarction of the metaphyses on either side of the knee is common and may lead to premature fusion of

the growth plates ● ON is common, particularly in the proximal femur and proximal humerus

●● SCD is the commonest cause of ON of the femoral head in children, and approximately 50% of all patients will develop ON by the age of 35 years

●● secondary OM: is most commonly due to Salmonella, usually complicating bone infarction: ● it may be difficult to distinguish clinically or radiologically between an infarct with infection, and one

without ● the presence of subperiosteal fluid and geographic rather than rim enhancement of lesions

are features more suggestive of osteomyelitis than acute infarction without superimposed osteomyelitis

●● MRI findings: ●● thalassaemia: in children, the medulla enlarges relative to the cortex, leading to bony expansion and

cortical thinning: ● in long bones, this results in the characteristic Erlenmeyer flask appearance ● MRI also demonstrates diffuse reduction of marrow SI on T1W/PDW images (Fig. 8.89a) and

marrow hyperintensity on FS/STIR images (Fig. 8.89b) due to marrow reconversion ● transfusion siderosis: may cause synovitis and arthropathy, resulting in typical degenerative changes

most commonly affecting the large joints: – several iron chelation therapy agents also have a recognised association with synovial and chondral

siderosis-associated arthropathy, metaphyseal oedema, splayed and blurred physeal/metaphyseal junctions, widened growth plates and subchondral cystic defects252,253

– the marrow iron burden can be quantified using FS R2 relaxometry techniques255 ●● SCD: marrow reconversion results in generalised marrow SI changes, as with thalassaemia

(Figs 8.89c, d): ● bone infarction: MRI shows medullary oedema (Figs 8.89e, f ) with associated periostitis and adjacent

soft-tissue inflammation, making differentiation from OM difficult: – with healing, these areas assume low T1 and T2/STIR SI due to fibrosis and medullary sclerosis

● ON: MRI initially demonstrates infarction as epiphyseal oedema, which progresses to the typical features of ON (Figs 8.89c, d), eventually resulting in secondary OA

● chronic ischaemia or multiple small infarctions produce cortical thickening, which is both endosteal and periosteal resulting in narrowing of the marrow cavity

● splitting of the cortex may give rise to a bone-within-a-bone appearance (Fig. 8.89g), while secondary myelofibrosis causes medullary sclerosis

● secondary OM: is 100 times more common than in the general population with Salmonella the most common pathogen, appearing as poorly-defined marrow oedema and subperiosteal fluid (Figs 8.89h, i): – regions of periosteal and marrow enhancement on post-contrast FS T1W images are strongly

associated with infection – subperiosteal fluid and irregular geographic enhancement (as opposed to rim enhancement) suggest

osteomyelitis rather than bone infarction

●● PRV: results in excess erythroid, myeloid and megakaryocytic elements with elevation of the haemoglobin level to above 17.5 g/l and a RBC count persistently greater than 6.0 × 1011: ●● any skeletal change results from occasional bone infarction due to increased viscosity of the blood ●● the superimposition of leukaemia and myeloid metaplasia is relatively common, and MRI can

readily depict conversion of cellular marrow to fatty marrow and vice versa in PRV and myeloid metaplasia

●● myelofibrosis: primary myelofibrosis is a slowly progressive marrow disorder of unknown aetiology, which affects males and females equally, with an age range of 20-80 (median age 60 years): ●● it should only be diagnosed once causes of secondary myelofibrosis have been excluded ●● clinically: the disorder presents insidiously with weakness, dyspnoea and weight loss ●● antecedent PRV is common, but obliteration of the marrow by fibrosis or bony sclerosis soon leads to a

moderate normochromic, normocytic anaemia ●● the natural history is one of slow deterioration, with death typically occurring 2-3 years after diagnosis

●● secondary myelofibrosis: is the end-stage of the myeloproliferative syndrome and occurs to a greater or lesser degree in leukaemia, lymphoma, Gaucher’s disease, toxic exposure, carcinomatosis and even infection

●● MRI findings: ●● radiographic bone sclerosis manifests on MRI as reduced marrow SI on all pulse sequences, which is also

contributed to by marrow fibrosis ●● typically, this is diffuse (Fig. 8.90a) or occasionally patchy (Fig. 8.90b), occurring most often in the axial

skeleton, pelvis and metaphyses of the femur, humerus and tibia ●● sclerosis is due to trabecular and endosteal new bone formation, resulting in reduced marrow diameter

●● Gaucher’s disease: is the most common lipid storage disorder and is due to a genetic enzyme (glucocerebrosidase) deficiency, which results in the accumulation of the lipid glucocerebroside in the lysosomes of monocytes and macrophages

●● these engorged cells are called Gaucher cells and their accumulation within a variety of organ systems accounts for the symptoms of the disorder

●● many of those affected are Ashkenazi Jews (approximately 1 of every 400-600), but all races are vulnerable ●● 3 types are recognised: the common type 1, which is non-neuronopathic and termed ‘adult type’, although

approximately half of the patients are diagnosed before 10 years of age, and the rare neuronopathic types 2 (acute) and 3 (subacute)

●● skeletal changes occur in more than 80% of Gaucher type 1, and are due to a combination of marrow storage disorder and bone crises, resulting in substandard growth, bone deformity, chronic bone pain, pathological fracture, osteopenia, vertebral collapse, ON, osteosclerosis and bone crises

●● clinically: both dull bone pain and acute painful crises occur, the latter being characterised by acute episodes of severe skeletal pain, fever, leucocytosis and raised ESR

●● MRI findings: ●● lipid storage defects: result in large amounts of lipid in the marrow spaces, causing loss of normal

modelling of the long bones in childhood, resulting in the Erlenmeyer flask appearance

●● acute bone crises: are due to marrow infarcts and manifest as marrow oedema on MRI: ● they must be differentiated from osteomyelitis, which also complicates Gaucher’s disease

●● ON of the femoral and humeral heads is common ●● MRI is useful in evaluating the extent of marrow infiltration, manifesting as either homogeneous or

inhomogeneous areas of reduced SI on T1W, T2W FSE and T2W GRE images (Figs 8.91a, b) as compared to subcutaneous fat, and hyperintensity on STIR

●● focal areas of increased T2W SI are thought to represent active bone lesions ●● ON results in osteoarthritis and vertebral body collapse ●● quantitative evaluation of marrow involvement can be achieved by the use of quantitative chemical

shift imaging (QCSI), which works by determining the reduction of the fat fraction in bone marrow adipocytes

●● leukaemia: acute lymphocytic leukaemia (ALL) accounts for 80%, acute myeloblastic leukaemia (AML) for 10% and other types for 10% of cases: ●● acute leukaemia: is the commonest malignancy of childhood, while chronic leukaemias predominate in

adults but sometimes terminate in an acute blastic form ●● adults are most commonly affected by ALL and chronic myeloid leukaemia (CML) ●● chronic lymphocytic (lymphoid) leukaemia (CLL): is a disease of the elderly, characterised by enlargement

of the spleen and lymph nodes with skeletal involvement being rare, except as a terminal event ●● lymphoma: secondary bone involvement in NHL and Hodgkin’s disease (HD) usually indicates stage IV

disease: ●● 1-4% of patients with HD present initially with a skeletal lesion, whereas the prevalence of bone

involvement at autopsy is almost 75% ●● however, at clinical assessment, bone involvement is reported in 15-20% of cases, especially in the more

aggressive histological subtypes, and is more commonly multi-focal ●● the most common radiological appearance is a lytic lesion, but sclerotic and mixed patterns are recognised ●● NHL embraces a variety of follicular and diffuse lymphocytic lymphomas, representing a monoclonal

proliferation of B-cells, T-cells or histiocytes ●● secondary skeletal involvement occurs in 15-25% and sclerotic lesions are less commonly seen than in HD

●● MRI findings: ●● MRI typically demonstrates diffuse marrow infiltration with reduction of T1W SI in affected areas in

both leukaemia and lymphoma (Figs 8.92a, b)

●● a change from normal to nodular to diffuse low SI can be seen with disease progression, together with an increase in the extent of SI abnormality

●● MRI can also identify complications of treatment such as ON ●● a particular focal lesion occurring in AML is granulocytic sarcoma (chloroma), which is usually located in

the skull, spine, ribs or sternum of children: ● this is an expanding geographical tumour caused by a collection of leukaemic cells (Figs 8.92c, d),

and reported to occur in 4.7% of patients

●● mastocytosis: is a disorder of mast cell proliferation within different body tissues that can result in a variety of clinical syndromes, including urticaria pigmentosa, systemic mastocytosis and mast cell leukaemia

●● urticaria pigmentosa: accounts for 80-90% of cases and is a self-limiting condition that typically affects children

●● systemic mastocytosis: accounts for <10% of cases and usually occurs in adults: ●● clinical symptoms resemble lymphoma or leukaemia and the condition can be fatal ●● the liver, spleen, lymph nodes, skin and bone marrow can all be affected ●● skeletal changes are usually evident in early adult life and affect 10% of patients with urticaria pigmentosa

alone, but 70% of patients with systemic mastocytosis ●● mast cell-associated histamine secretion stimulates fibroblastic activity and osteoid formation, resulting in

osteosclerosis, while increased heparin secretion can result in osteopenia and osteoporosis ●● the resulting pattern may be osteosclerotic, lytic, osteoporotic or mixed, and focal or diffuse, and the lytic

and osteoporotic forms may present with pathological fractures, while the sclerotic form is associated with a more aggressive disease

●● MRI findings: ●● MRI may be normal, or show a variety of marrow infiltration patterns, including homogenous and non-

homogeneous areas of reduced SI on T1W images (Figs 8.93a, b)

●● T2 and STIR marrow SI are variable and may be hyperintense or hypointense, depending upon the degree of marrow infiltration and fibroblast proliferation, while sclerotic lesions are hypointense on all sequences

●● mast cell marrow infiltration result in increased post-contrast enhancement ●● it may be difficult to differentiate between low degree mast cell infiltration and normal red marrow ●● the spine is always affected (Figs 8.93c, d)

●● plasmacytoma: is apparently solitary at presentation and accounts for 3-5% of patients with plasma cell dyscrasias

●● it may remain localised for many years, but more than 30% progress quite rapidly to generalised myelomatosis (multiple myeloma, MM) and it is unusual for a patient to persist with a solitary plasmacytoma for more than 10 years

●● clinically: presentation with pain is common, but uncomplicated plasmacytoma may be asymptomatic: ●● although presentation below 40 years of age is unusual, the age of presentation tends to be on average

10 years earlier and the age range wider than in MM ●● as plasma protein changes are related to the total tumour mass, protein electrophoresis is often normal and

the ESR normal or only slightly elevated ●● sites of involvement are typically those with persistent red marrow and include the axial skeleton (thoracic>

lumbar>sacrum>cervical), pelvis, proximal femur, proximal humerus and ribs, with peripheral lesions being rare

●● radiographic appearances of flat and long bone lesions can vary from non-aggressive to highly aggressive ●● MRI findings:

●● plasmacytoma is typically lytic and destructive, therefore having intermediate T1W SI (Fig. 8.94a), increased FS T2W/STIR SI (Fig. 8.94b)

●● the lesion arises in the medulla and the imaging features suggest a relatively slow growth rate, with an often well-defined margin, cortical thinning and bone expansion (Figs 8.94a, b)

●● apparent trabeculation (Fig. 8.94c) or a ‘soap bubble’ appearance is common and an associated soft-tissue mass is frequently seen (Fig. 8.94d), the lesion enhancing following contrast (Fig. 8.94e)

●● following the diagnosis of plasmacytoma, MRI of the spine and pelvis is indicated to identify additional lesions, which may be seen in up to 80% of cases

●● appendicular plasmacytoma may rarely demonstrate a ‘mini brain’ appearance on MRI, this appearance being due to localised bony destruction and the formation of radially orientated thickened trabeculae266

●● multiple myeloma (MM): is the commonest primary malignant neoplasm of bone and is the predominant plasma cell dyscrasia, accounting for approximately 1% of all malignant disease and 10% of haematological malignancies

●● clinically: 75% of affected patients are over 50 years of age with a median age of 65 years, and approximately 3% of patients present before the age of 40 years: ●● there is a male predominance of up to 2:1 and fever, pain, backache and weakness are common symptoms ●● with generalised skeletal involvement, production of an abnormal paraprotein leads to a wide m-band on

plasma electrophoresis, resulting in raised ESR, frequently over 100 mm/h ●● production of light-chain immunoglobulins results in Bence-Jones proteinuria in over 50% of patients ●● widespread involvement of the skeleton is present in 80%, the axial skeleton and proximal ends of the limb

bones being particularly involved ●● MRI findings:

●● the MRI appearances in MM are variable ●● a normal marrow pattern may be seen at presentation in 50-75% of patients with early untreated (stage 1)

MM and in 20% of patients with advanced (stage 3) MM ●● a focal pattern consists of localised areas of decreased SI on T1W images (Fig. 8.95a) with corresponding

increased SI on FS T2W/STIR images (Fig. 8.95b), which is indistinguishable from metastatic disease ●● occasionally, focal lesions may be relatively hyperintense on T1W and be identified only on T2W images ●● a combined focal and diffuse pattern is seen as focal T1 hypointense lesions on a background of diffusely

hypointense marrow, with the focal lesions better demarcated on FS sequences

●● the diffuse pattern manifests as generalised reduction of marrow SI on T1W images (Fig. 8.95c), marrow hyperintensity on FS T2W and STIR images and diffuse enhancement following contrast (Fig. 8.95d)

●● in high-grade diffuse involvement (>50% volume on bone marrow biopsy), the T1W SI is similar to that of the intervertebral discs, whereas in intermediate-grade involvement, the T1W SI reduction is hard to identify on standard imaging, and infiltration can be quantified using the percentage increase in SI on post-contrast enhanced imaging270

●● finally, a ‘variegated’ pattern is described, which consists of multiple tiny foci of reduced SI on T1W (Fig. 8.95e) and hyperintensity on T2W/STIR images on a background of normal marrow, a pattern which is almost always seen in early disease

●● these patterns have some prognostic value, in that patients with diffuse marrow abnormality on MRI will have a poorer outcome than those with a normal MRI pattern

●● dynamic contrast-enhanced MRI can reflect the vascularity and angiogenesis of myelomatous lesions, and can be used as a predictor of survival

●● bone infarction: is a term used to describe ON occurring in non-epiphyseal sites, where the term avascular/ aseptic necrosis tends to be used

●● predisposing factors: are the same as for AVN and include steroids, trauma, sickle cell disease, metabolic/ endocrine disorders, vasculitides, alcoholism and radiotherapy

●● the metaphyses of the femur, tibia and humerus are most commonly involved in addition to the pelvis ●● cystic bone infarcts:272 cystic degeneration may occur in medullary bone infarcts, which may mimic lytic

bone tumours: ●● patients commonly present with mild pain, most commonly involving the humerus or femur ●● most lesions are described in women, and range from 1.5 to 12 cm in dimension

●● MRI findings: ●● relatively early infarcts may be associated with prominent marrow oedema (Figs 8.96a, b), but with the

development of the infarct, the appearances become typical

●● mature infarcts have a geographic/serpentine outline, with a low SI margin on T1W (Fig. 8.96c) and hyperintense margin on STIR (Fig. 8.96d)

●● the ‘double-line’ sign may be seen on T2W images (Fig. 8.96e) and marginal enhancement can be seen following contrast

●● the centre of the infarct may show a variety of SI characteristics, as described in the Mitchell classification:

● class A: high T1W and intermediate T2W SI consistent with fat (Figs 8.96c, d) ● class B: high T1W and high T2W SI consistent with blood ● class C: low T1W and high T2W SI consistent with fluid (Figs 8.96f, g) ● class D: low T1W and low T2W SI consistent with fibrous tissue (Figs 8.96h, i)

●● complications of mature infarcts include sarcomatous transformation, which is suggested by the development of a region of aggressive marrow replacement engulfing the infarct

●● cystic infarcts: may be mildly expansile and have reduced T1W SI (Fig. 8.96f), being uniformly hyperintense on T2W sequences (Fig. 8.96g) and showing no enhancement following contrast

●● soft-tissue and bone tumours may be treated with radiotherapy as a sole method, or as an adjunct to surgery and chemotherapy

●● radiation osteitis: refers to mild forms of bone injury, including oedema and periostitis, while radiation ON involves larger zones of bone loss and bone death

●● pathologically: irradiation causes damage to osteoblasts, resulting in decreased bone matrix production and unopposed osteoclastic resorption: ●● the threshold for osteoblast injury is thought to be ~30 Gy with cell death occurring at ~50 Gy ●● there may also be an effect on bone due to radiation-induced vascular injury ●● radiotherapy also affects the haematopoietic elements of the marrow, resulting in myeloid depletion ●● all of the changes are limited to the radiotherapy field, and radiographic appearances vary somewhat

according to the anatomical site ●● the radiographic changes associated with irradiated bone range from osteopenia (at approximately 1 year

post-irradiation) to ON ●● approximately 3 years after exposure, recovery of osteoblastic activity results in irregular bony repair ●● the changes in bone resulting from radiotherapy are termed radiation osteitis, while cell death results in

radiation ON or osteoradionecrosis ●● complications of radiation osteitis include stress and pathological fracture ●● in the region of the SIJ, radiation osteitis is distributed mainly on the iliac side, while insufficiency fractures

occur on the sacral side ●● sclerosis and trabecular coarsening in radiation osteitis/ON results in a similar radiological appearance to

that of Paget’s disease, but unlike Paget’s, the bone is not expanded and there is an abrupt transition to nonirradiated bone, rather than a flame-shaped margin275

●● MRI findings: ●● acute changes include transient increase in marrow SI on STIR due to marrow oedema (Fig. 8.97a),

necrosis and haemorrhage and can be seen within 8 days of treatment ●● myeloid depletion is associated with replacement of red marrow with fat (yellow marrow) and conversion

of red to yellow marrow may be complete as early as 6-8 weeks following radiotherapy ●● consequently, irradiated marrow appears hyperintense on T1W/T2W FSE images compared to adjacent

uninvolved marrow and hypointense on FS sequences ●● radiation osteitis may result in irregular cortical and trabecular thickening (Figs 8.97b, c), with tiny

cortical lytic areas being characteristic ●● all of the changes are limited to the radiation field ●● reconversion to red marrow is manifest by a progressive reduction in marrow SI on T1W images,

and is dose dependent but may be enhanced by the use of GCSF

●● post-radiation sarcoma (PRS): is now the preferred term (as opposed to radiation induced sarcoma) for bone and soft-tissue sarcomas that develop following previous radiotherapy

●● a history of radiation therapy ●● the development of a neoplasm within the radiation field and 5% isodose line ●● a latent period of several years (minimum 3-4 years) ●● histological proof of a sarcoma, which differs significantly from that initially treated

●● the commonest treated tumours resulting in the development of PRS are breast carcinoma, lymphoma, head and neck cancers and gynecological malignancies, accounting for the increased incidence in women

●● clinically: the mean age at presentation is the 6th decade ●● it was previously considered that a minimal dose of 30 Gy was required to induce a PRS, but there is now

evidence that lower doses carry a significant risk of PRS, particularly in younger patients ●● PRS frequently occur at the periphery of the radiation field, but there is also a small increased incidence

distant to the field, and the concurrent use of chemotherapy increases the risk of sarcoma development280,281 ●● pathologically: the commonest PRS is OS, followed by spindle cell sarcoma/fibrosarcoma, together

accounting for 90% of cases with 10% being chondrosarcoma, and the commonest sites are the pelvis and shoulder girdle

●● the majority of PRS are high-grade or poorly-differentiated, typically carrying a poor prognosis, with a mean 5 year survival of 45%279

●● typical imaging features include bone destruction, soft-tissue mass, matrix mineralisation and periosteal reaction (Figs 8.98a-c)

●● there may also be evidence of radiation change in the underlying bone (osteitis and marrow infarction), such as fatty replacement of normal red marrow

●● the lesions have no specific SI characteristics, being of intermediate SI on T1W (Fig. 8.98a) and heterogeneous increased SI on PDW/T2W/STIR images (Figs 8.98b, c)

●● Paget’s disease: is declining in prevalence in recent years, affecting 0.3-3% of the population and 1-10% over the age of 85 years in Europe, with a male to female ratio of 3:2286

●● it can be inherited in an autosomal dominant pattern with incomplete penetrance in 20% of patients, and a genetic mutation has been identified in a third of all patients

●● pathologically: it is characterised by excessive and abnormal remodelling of bone, with 3 phases of the disease described, which represent a continuum rather than discrete episodes: ●● phase 1: lytic (incipient-active) in which there is predominantly osteolysis ●● phase 2: mixed (active) with osteoblastic activity superimposed on active osteolysis, with eventually

predominance of osteoblastic activity ●● phase 3: blastic (inactive) phase, in which osteoblastic activity subsides ●● the lytic phase is characterised radiologically by a ‘blade-shaped’ leading edge, while osteoblastic activity

results in cortical and trabecular thickening, and eventually bone enlargement and deformity ●● associated bone marrow changes include replacement of normal yellow marrow by fibrovascular tissue in

the active phase, with a return to diffuse fatty marrow in the late inactive phase ●● almost any bone can be involved, although Paget’s disease predominantly affects the axial skeleton, with the

pelvis (30-75%), spine (30-75%) and skull (25-65%) being the commonest sites ●● proximal long bone involvement is also common with the femur affected in 25-35% of cases, and additional

relatively common sites include the shoulder girdle (humerus, 31%; scapula, 24%; clavicle, 11%) ●● long bone involvement is typically initially subarticular with extension into the diaphysis:

●● primary diaphyseal Paget’s is rare but reported to occur in the tibia ●● the disease is monostotic in 10-35% of cases, more commonly when involving the axial skeleton, while

polyostotic disease (65-90% of cases) has a predilection for the right side of the body and lower limb involvement

●● clinically: 20% of patients are initially asymptomatic, while symptoms of active disease include bone pain, tenderness and increased warmth and later, bone enlargement and deformity are common: ●● stress fractures, also known as banana fractures or pseudo-fractures may develop in bowed long bones,

seen as incomplete transverse fracture lines perpendicular to the cortex ●● subarticular Paget’s disease is thought to result in accelerated osteoarthritis, further exacerbated by altered

mechanics secondary to osseous deformity, but osteophyte formation is not a major feature

●● acetabular involvement may result in protrusio acetabuli ●● pain may also be related to pathological/stress fracture or sarcomatous degeneration

●● a combination of Paget’s disease, myopathy and fronto-temporal dementia is seen in Valosin-containing protein (VCP) disease287

●● juvenile onset Paget’s disease: is an autosomal dominant disorder that has been linked to a genetic mutation that encodes the signal peptide of RANK, and therefore affects bone remodelling and repair pathways288

●● MRI findings: ●● cortical and trabecular thickening (Figs 8.99a-e) and cortical hyperintensity due to increased vascularity

(Fig. 8.99d) ●● marrow SI is variable, being normal in the majority of cases (Figs 8.99c, e) ●● in the early/active phase, heterogeneous reduced T1W SI (Fig. 8.99f) with corresponding increased FS

T2W/STIR SI (Fig. 8.99g) may be seen due to fibrovascular tissue in the marrow ●● a ‘flame-shaped’ hyperintense leading edge may be seen on FS T2W/STIR images (Fig. 8.99h) ●● in the late phase, there may be reduced marrow SI on all pulse sequences, due to marrow sclerosis and

fibrosis ●● following contrast, cortical and marrow enhancement may be seen with active disease (Fig. 8.99i), and

DCE MRI can be used as a measure of disease activity and response to bisphosphonate therapy289

●● bone sarcomas: arising after the age of 50 years are not uncommonly secondary to Paget’s disease and at least 50% of these are OS, while fibrosarcoma/spindle cell sarcoma account for 25%, the remainder being CS, angiosarcoma, anaplastic sarcoma, lymphoma and, occasionally, GCT

●● the overall prevalence of malignant change is reducing, likely to be under 1% with the incidence increasing to 5-10% in patients with widespread, long-standing Paget’s disease

●● however, sarcoma can also occur in a patient with monostotic disease ●● most patients are >45 years at diagnosis and the sex incidence of Paget’s sarcoma is similar to that of the

primary disease, with men affected twice as often as women ●● the commonest sites: are the femur, pelvis and humerus, while Paget’s sarcoma is rare in the spine and may be

multi-focal in 2.4-17% of cases ●● clinically: development of sarcoma is suggested by a change in type or severity of bone pain, and sometimes

by an enlarging mass or a pathological fracture ●● MRI findings:

●● imaging typically demonstrates an extensive area of bone destruction with a large soft-tissue mass, and features of underlying Paget’s disease (Figs 8.100a, b)

●● the presence of osteoblastic matrix will result in areas of low SI on all pulse sequences ●● MRI is extremely valuable in identifying sarcomatous degeneration, based on the presence of marrow

infiltration on a T1W image, and this should be suspected even in the absence of a soft-tissue mass (Fig. 8.100c)

●● conversely, normal marrow SI on T1W excludes sarcoma with a very high degree of certainty, this being a particularly important sign in the presence of pathological fracture (Fig. 8.100d)

●● prominent inhomogeneous enhancement may be evident on post-contrast studies

●● pseudosarcoma: refers to a situation in which there is focal proliferation of pagetic periosteal new bone at the site of Paget’s disease

●● clinically: it presents with pain and swelling, typically affecting bones that have long-standing Paget’s disease ●● the femur and tibia are most commonly involved, with radiographs demonstrating spiculated periosteal new

bone formation into the soft tissues ●● the clinical and radiological features are indistinguishable from Paget’s sarcoma and may show destruction of

the underlying cortex

●● haemorrhagic giant-cell rich pseudosarcoma may result in a hypervascular soft-tissue mass overlying bones affected by Paget’s disease, and must be distinguished from other giant-cell rich tumours, including sarcomas

●● MRI findings: ●● underlying features of chronic Paget’s disease, with periosteal new bone formation or a surface-based

soft-tissue mass surrounding the bone with variable T1W and T2W SI depending upon the type of tissue contained

●● the mass may have intermediate T1W SI with mild T2W hyperintensity, or show the SI of normal marrow

●● a spiculated periosteal reaction may be seen

●● GCT: in Paget’s disease (PD-GCT) is a rare association, and is typically a benign lesion that can respond well to steroid treatment

●● however, the presence of PD-GCT is associated with a younger age at Paget’s disease diagnosis, more severe disease which is more commonly multi-focal, and a poorer 5 and 10 year survival rate than occurs in Paget’s disease without PD-GCT

●● PD-GCT is multi-focal in 25% of cases, compared to 1% of non-pagetic GCT

●● unlike GCT in non-pagetic bone, which typically involve the appendicular skeleton, particularly the knee region, PD-GCT most commonly occurs in the skull or facial bones, but may be seen at other locations, usually presenting in elderly patients with polyostotic involvement

●● males are more frequently affected than females (in contrast to non-pagetic GCT) ●● MRI findings:

●● a lytic expansile lesion with well-defined margins, low-to-intermediate T1W and T2W SI, with contrast enhancement of solid components

●● lesions may contain areas of cystic or secondary ABC change and haemorrhage

●● sarcoidosis: is an inflammatory disorder of unknown aetiology, characterised by the development of noncaseating granulomata in various tissues, with no other causes of granulomatous disease identified

●● the commonest involved organs are the lungs (90% of patients), lymph nodes, skin and eyes ●● skeletal involvement: is reported in 1-13% of cases and in 60% is present at initial diagnosis,295 involving

bones, joints and soft tissues ●● Lofgren syndrome: consists of arthralgia, erythema nodosum and bilateral hilar lymphadenopathy ●● granulomatous arthropathy: is reported in 10-35% of cases, while sarcoid myopathy occurs in 1.4% of

patients ●● joint involvement: is typically polyarticular and may be acute or chronic ●● acute arthritis: is symmetrical and may be migratory or additive, most commonly involving the knees, ankles,

wrists, elbows and PIP joints ●● MRI findings:

●● cannot reliably differentiate between osseous sarcoidosis and bone metastases, particularly in the spine and pelvis (Figs 8.101a, b)298

●● small bone lesions: radiographically detectable lesions typically have a ‘lacy’ lytic appearance: ● MRI may demonstrate radiographically occult marrow lesions, extraosseous extension of granulomata

and periosseous soft-tissue involvement ● phalangeal cysts occur in 14% of patients, and distal phalangeal sclerosis, dactylitis and subchondral

bone destruction may be seen ●● large bone lesions: may be lytic, sclerotic or occult, while MRI demonstrates poorly-defined or well-

defined lesions of various size and shape (Figs 8.101c, d), with reduced T1W SI and variable, although usually increased T2W/STIR SI:

● variable contrast enhancement is seen with cortical destruction and extraosseous extension being rare, and resolution of sarcoid lesions may occur on follow-up studies

● after treatment, recurrent lesions may demonstrate a T2W hyperintense ‘halo’ around the lower SI fibro-fatty centre of the treated lesion, this sign also being described in metastatic disease299

●● granulomatous arthropathy: non-specific findings of tenosynovitis, tendonitis, bursitis and synovitis ●● nodular sarcoid myopathy: manifests as focal intramuscular masses, often at the musculotendinous

junction: ● the masses may be multiple and bilateral, commonly involving the lower limbs (Fig. 8.101e) ● on T2W and post-contrast T1W images, the lesions have a hyperintense periphery and a lower SI

centre ●● generalised sarcoid myopathy: a non-specific finding of proximal muscle atrophy and fatty replacement,

similar to polymyositis ●● additional features: include subcutaneous granulomatous infiltration, skin nodules and soft-tissue masses,

with associated lymphadenopathy

●● intramedullary osteosclerosis: is a rare disorder of unknown aetiology associated with endosteal new bone formation mainly affecting the tibial shaft in adults, and most commonly females

●● clinically: it presents with chronic leg pain associated with physical activity, thus mimicking a stress injury

●● radiographs: demonstrate diaphyseal cortical and endosteal thickening without a prominent periosteal reaction, and usually involving the tibial shaft, although other lower limb bones and the humerus may also be affected, and the condition may be bilateral

●● intramedullary osteosclerosis has similar imaging features to ribbing disease and Camurati-Engelmann disease, but is not associated with an autosomal dominant inheritance or multi-organ involvement

●● MRI findings: ●● low medullary SI on all pulse sequences (Figs 8.102a-c) with minimal associated increase in medullary

and soft-tissue SI on FS T2W/STIR images (Fig. 8.102c) which may enhance following contrast (Fig. 8.102d)

●● melorheostosis: is a rare sclerosing dysplasia of bone in which typically one or several contiguous bones are involved, often following a sclerotomal distribution

●● the lower limbs are more commonly affected than the upper limbs, with axial skeletal involvement being rare

appearance on radiographs: ●● soft-tissue masses are also a recognised feature, being reported in 27% of cases, usually in continuity with

or adjacent to areas of bone involvement and being formed of various combinations of osseous, chondral, fibrolipomatous and vascular elements

●● extension of bone disease into adjacent joints is also recognised,305 being reported in 35% of cases

●● clinically: it may be asymptomatic and identified incidentally on imaging studies, or present with joint contracture or soft-tissue masses, which may be mistaken for sarcoma

●● rarely, osteosarcoma and fibrosarcoma may develop on a background of melorheostosis, while desmoid tumour, capillary haemangioma, neurofibromatosis, tuberous sclerosis, osteopoikilosis and hypophosphataemic rickets have a recognised association

●● MRI findings: ●● bone lesions: appear as well-defined areas of undulating cortical (Fig. 8.103a) and endosteal/medullary

(Fig. 8.103b) sclerosis, showing signal void on all pulse sequences with no associated reactive changes ●● soft-tissue masses: have mixed SI on all pulse sequences due to their varied histological content:

● areas of signal void due to mineralisation are seen in 70% of cases (Fig. 8.103c) ● areas of fatty SI are reported in 90% of cases (Fig. 8.103c), while intermediate SI is the predominant

pattern in 60% of cases (Fig. 8.103c) ● the lesions have poorly-defined margins (80%), commonly with involvement of subcutaneous fat

(Fig. 8.103d) or deep muscles ● intra-articular extension is also well demonstrated (Fig. 8.103e) ● contrast enhancement of the soft-tissue lesions is variable, and there may also be enhancement around

para-articular masses (Fig. 8.103f)

●● skeletal muscle fibres: are grouped into fascicles, which are grouped into muscles ●● normal skeletal muscle has intermediate SI, which is hyperintense to water and hypointense to fat on

T1W/PDW sequences (Figs 8.104a, b), and markedly hypointense to water and fat on T2W sequences (Fig. 8.104c)

●● the normal marbled appearance of muscle is due to the presence of fat-containing septa separating the fascicles

●● at 3T, prominent chemical shift artefact can be seen at muscle:fat interfaces and should not be mistaken for soft-tissue oedema (Fig. 8.104d)

●● normal tendons: appear hypointense on all standard sequences (Figs 8.104a, b) ●● advanced imaging techniques:

●● DTI: enables detailed evaluation of muscle architecture, and muscle fibres can be visualised with fibre tracking

●● blood-oxygen-level dependent imaging (BOLD): is used to quantify muscle microvasculature and metabolism, while DCE MRI can evaluate perfusion

●● MR spectroscopy: allows measurement of intramuscular metabolites

●● muscle strain: is usually secondary to indirect trauma (excessive stretch or tension), typically at the musculotendinous junction in young adults, this representing the point of maximum weakness

●● acute muscle injury: less commonly results in a myofascial or epimysial strain, seen as peripheral muscle oedema at the fascial interface

●● it most commonly affects muscle groups that cross 2 joints, perform primarily eccentric contraction and which contain a predominance of fast twitch (type 2) muscle fibres

●● muscles injuries: most commonly involve rectus femoris, the hamstrings and medial gastrocnemius ●● pathologically: a combination of torn muscle fibres, inflammation, oedema and haemorrhage is seen ●● clinically: strain results in acute muscle pain and swelling following a period of strenuous physical activity,

which typically resolve within 2 weeks ●● muscle strains: may be classified into 3 grades:

●● grade 1: the commonest (75% of cases) and typically associated with a microscopic injury (<5% muscle fibre disruption) and no significant loss of muscle strength

●● grade 2: partial thickness, macroscopic tears with continuity of some muscle fibres at the site of injury, associated with some loss of muscle strength:

● may be subdivided into low-grade (<1/3 fibres torn), moderate (>1/3 and <2/3 fibres torn) or high-grade (>2/3 fibres torn)

●● grade 3: rarer than grade 1 and 2 injuries, characterised by complete disruption of the musculotendinous junction, with/without muscle retraction and associated with loss of muscle function:

● retraction of muscle fibres may result in a palpable defect or focal mass, mimicking a tumour (Figs 8.105a, b)

● grade 3B injuries: represent avulsion injuries of the musculotendinous unit from the bony attachment310

●● specific muscle injuries: ●● pectoralis major: most commonly seen in weight-lifters,311 following falls or as the result of a direct injury

during a road traffic accident ● partial tears are more common than complete tears and typically occur at the musculotendinous

junction, whereas complete tears occur at the muscle insertion (see Chapter 1) ● tears of the muscle belly are most frequently the result of direct trauma ● isolated injury of the upper clavicular portion has been identified in wrestlers

●● hamstring muscles:309,312 are the commonest injured muscles in sprinting and jumping athletes: ● the majority are partial tears, most commonly involving biceps femoris, followed by the

semimembranosus and semitendinosus although up to a third involve more than 1 muscle ● each hamstring tendon extends for almost the whole length of the muscle, therefore musculotendinous

strains can occur at either end of the muscle (proximal 33%, distal 13%), or within the muscle itself (53%) (Fig. 8.105c)

● 5 types of proximal hamstring injury have been described:313 – type 1: osseous avulsions, representing apophyseal injuries in skeletally immature patients – type 2: injuries at the myotendinous junction (Fig. 8.105c) – type 3: incomplete tendon avulsion from bone – type 4: complete tendon avulsions without significant retraction – type 5: complete tendon avulsions with retraction (type 5a without sciatic nerve tethering,

and type 5b with sciatic nerve tethering), the degree of tendon retraction being usually less than 10 cm

● MRI has some role in determining the prognosis following hamstring injuries:314 – injury to the semimembranosus proximal myotendinous junction or proximal free tendon indicates

a stretching injury, which may require 6-24 months recovery time – injury isolated to the long head biceps femoris, or combined with other muscles characterises a

typical hamstring strain with recovery in a few weeks – in sprinters, the proximity of the long head biceps tendon injury to the ischial tuberosity and the

length of muscle oedema on MRI are predictive of recovery time, with longer recovery expected when the proximal extramuscular part of the tendon is involved compared to the myotendinous junction or intramuscular tendon

●● quadriceps: injuries are commonly seen as running or football injuries, the vast majority involving the rectus femoris:315

● injury patterns to the rectus femoris require an understanding of the complex anatomy of the musculotendinous unit316

● the tendon of the direct head is short, thin and broad-based, blending with the anterior fascia of the muscle in the proximal thigh, while the tendon of the indirect head extends distally into the centre of the muscle belly in a sagittal orientation as far the distal third of the muscle (Fig. 8.105d)

● in addition to injuries of the rectus femoris myotendinous unit, myofascial injury represents a distinct lesion estimated to account for ~15% of rectus femoris injuries in professional footballers

● intramuscular degloving injuries: represent a further subset in which there is separation of the inner bipennate component of the indirect head from the superficial unipennate component of the direct head317

● chronic repetitive rectus femoris injury may result in a painless mass in the anterior thigh mimicking a soft-tissue tumour (Figs 8.105a, b)

● factors predictive of poor prognosis following rectus femoris injury include: – proximal injuries, perifascial fluid, changes seen on T1W images and involvement of >50% of the

muscle cross-sectional area ●● gastrocnemius:308,309 injury most commonly affects the medial head (86%), being referred to as ‘tennis leg’

and involves the musculotendinous junction in 96% of cases (Figs 8.105e, f ): ● presents with sudden onset of calf pain in middle-aged individuals involved in racquet sports, skiing

and running and most are low-grade partial tears ●● plantaris muscle tears: may also occur, appearing on MRI as fluid/haematoma within or adjacent to the

muscle at the level of the knee joint, between the medial head of gastrocnemius and soleus muscles: ● plantaris injury can also involve the adjacent muscles in the posterolateral corner of the knee, and may

be associated with ACL rupture ● chronic injuries may present as a calf mass due to haematoma (Figs 8.105g, h)

●● soleus muscle tears: can occur with or without associated gastrocnemius tears and may be myotendinous or myofascial:

● a third of cases of ‘tennis leg’ involve dual muscle strains involving the medial head of gastrocnemius and the soleus

●● the throwing athlete: injuries of latissimus dorsi and subscapularis have been reported in professional baseball players, and teres major may also be involved

●● MRI findings: ●● grade 1 strain: increased SI on FS PDW/T2W/STIR images at the musculotendinous junction due to

oedema and haemorrhage, which may track along the muscle fascicles, producing a feathery margin (Figs 8.106a, b):

● perifascial fluid is reported in 87% of athletes with acute partial muscle injury ●● grade 2 strain: increased muscle SI on FS PDW/T2W/STIR images due to oedema and haemorrhage

(Figs 8.105e, f ): ● haematoma at the musculotendinous junction is a typical finding, as is perifascial oedema (Fig. 8.106c) ● an old second-degree strain may be recognised by the presence of low T2W SI due to haemosiderin/

fibrosis, and muscle atrophy indicating incomplete healing (Figs 8.106d, e) ●● grade 3 strain: complete discontinuity of fibres, commonly with associated fibre laxity (Figs 8.105a, b),

the gap being filled by haematoma (Fig. 8.106f): ● muscle atrophy may begin as soon as 10 days following the injury and may be irreversible by 4 months

(Fig. 8.106g) ●● rectus femoris injuries:

● direct head myotendinous injuries: manifest as oedema/fluid along the anterior potion of the proximal rectus femoris, predominantly between the anterior fascia and muscle belly

● indirect head myotendinous injuries: manifest as oedema/fluid tracking along the course of the central tendon (Figs 8.106a, b), which may be quite extensive with associated swelling of the muscle in severe cases

● myofascial injuries: most commonly occur at the posterolateral myofascial junction and manifest as peripheral muscle oedema extending to the fascia (Fig. 8.106h), usually in the proximal and midthirds of the muscle

● degloving injuries: fluid separating the inner bipennate muscle component surrounding the central tendon from the superficial unipennate component of the muscle, with/without retraction of the inner muscle belly (Figs 8.106i-k)

●● with healing, scar formation can result in tendon/fascial thickening, which is optimally demonstrated on T1W/PDW sequences (Fig. 8.106l) and may be associated with muscle atrophy (Fig. 8.106e)

●● muscle haematoma: may be either intermuscular or intramuscular ●● intermuscular haematoma: is more common and may be related to muscle strains:

●● the signal characteristics of intermuscular haematoma may not follow typical temporal patterns

●● intramuscular haematomas: are typically related to a single muscle and take longer to resolve (6-8 weeks) ●● in direct trauma, the size of an intramuscular haematoma does not necessarily correlate with the degree of

loss of function, and the grading system used in indirect muscle injury does not necessarily apply ●● MRI findings:

●● acute haematoma: resembles fluid, showing intermediate SI on T1W and increased SI on T2W/STIR images, although central low SI due to deoxyhaemoglobin may be seen on T2W sequences

●● subacute haematoma: has high SI on T1W images (Fig. 8.107a) due to methaemoglobin and also increased T2W/STIR SI (Fig. 8.107b), commonly with associated muscle oedema (Fig. 8.107b):

● may leave a residual fluid containing intramuscular pseudocyst, which most commonly involve the rectus femoris, semimembranosus or semitendinosus muscles

●● chronic haematoma: shows increased T1W SI (Fig. 8.107c) and T2W/STIR SI (Fig. 8.107d) and a peripheral low SI rim due to haemosiderin within the wall and surrounding fibrosis (Fig. 8.107e)

●● fluid-fluid levels may also be seen

●● muscle contusions: are usually caused by a direct blow and often occur in the context of contact sports, the injury occurring when the deeper layers of the muscle are compressed against the underlying bone

●● muscle fibre disruption leads to haematoma formation, and this is located deeper in the muscle than those occurring in grade 1 and 2 muscle strains, while oedema and haemorrhage result in muscle swelling

●● MRI findings: ●● the appearances may resemble muscle strain, seen as T2W and STIR hyperintense muscle oedema, often

with an ill-defined feathery appearance (Figs 8.108a, b) ●● features more suggestive of a contusion than muscle strain include changes at the site of trauma rather than

the myotendinous junction, and MRI abnormalities crossing muscles or compartments

●● DOMS: refers to muscular pain, soreness and swelling that follows unaccustomed physical exercise, and in athletes commonly occurs during pre-season training or early post-rehabilitation following injury

●● pathologically: it is thought to result from reversible structural damage at a cellular level secondary to an acute inflammatory reaction, and is not associated with any permanent muscle damage

●● clinically: symptoms occur 1-2 days following activity (in contrast to muscle strain, which results in immediate symptoms) and peak at 2-3 days, gradually subsiding by 1 week: ●● soreness is often associated with temporarily diminished muscle strength

●● MRI findings: ●● as for a grade 1 muscle strain, with feathery increased T2W/STIR SI due to interstitial muscle oedema at

the musculotendinous junction (Figs 8.109a, b) ●● however, unlike grade 1 muscle strain, the signal change may affect more than one muscle/compartment ●● perifascial fluid accumulations may occasionally be seen in the early phase ●● persistent signal change within the muscle suggests muscle strain, although rarely abnormal SI may be seen

for up to 80 days in DOMS

●● with healing, there is a gradual resolution of fluid SI within the muscle, between the fascicles and at the epimysium

●● signal abnormalities may persist after the athlete has returned to competition, particularly in cases of severe injury: ●● the risk of recurrent injury with persisting signal change is uncertain

●● T2W hypointensity may also be seen with healing, representing scar tissue and/or haemosiderin deposition ●● scar tissue typically forms at or adjacent to the musculotendinous junction or myofascial surface ●● fatty infiltration of muscle may occur in the late stages, typically adjacent to the scar and may

erroneously be considered to represent more extensive scarring unless T1W or FS sequences are used (Figs 8.106d, e, g)

●● compartment syndrome: may be acute or chronic, and is defined as increased tissue pressure within a closed myofascial space, with secondary reduced microcirculation and potential for irreversible neuromuscular damage

●● acute compartment syndrome: may occur following fractures, trauma, burns, extrinsic compression, severe muscle injury and occasionally excessive exercise and results in extensive oedema, haemorrhage and swelling: ●● it is a surgical emergency, requiring immediate decompression with little place for imaging in the acute setting ●● Volkmann’s ischaemic contracture: refers to a late complication of compartment syndrome in which

necrotic muscle and nerve tissue are replaced by fibrous tissue ●● in athletes, compartment syndrome may occur secondary to muscle rupture (e.g. biceps brachii

compartment of the arm and flexor compartment of the forearm, the superficial posterior compartment or peroneal compartment of the leg) or in the absence of muscle rupture (e.g. triceps and deltoid muscles of weight-lifters and the anterior compartment of the legs in footballers)

●● chronic compartment syndrome: may result from exertional causes (chronic exertional compartment syndrome (CECS), exercise or occupational overuse) or non-exertional causes (e.g. a mass lesion or infection): ●● in athletes, chronic compartment syndrome most commonly affects the lower leg, with anterior and lateral

compartments most frequently affected,322 followed by the thigh, forearm and foot ●● chronic exertional compartment syndrome is frequently bilateral and may involve multiple compartments

●● clinically: acute compartment syndrome causes severe pain out of proportion to the degree of injury, while chronic exertional compartment syndrome presents with aching and tenderness during or immediately after exercise, which resolves with rest: ●● in both cases, arterial pulses are maintained, although there is impairment of venous and lymphatic drainage ●● late features include deficits of motor and sensory nerve function due to muscle and nerve ischaemia

●● MRI findings: ●● acute: increased size of the muscle compartment with increased FS T2W FSE/STIR SI due to oedema ●● subacute: increased T1W SI due to foci of haemorrhage ●● chronic: increased T1W SI due to fatty replacement (Fig. 8.110a), decreased T1W SI due to fibrosis/dystrophic

calcification, decreased muscle volume due to atrophy and/or fibrosis and fascial thickening (Fig. 8.110b) ●● perfusion of injured muscle may be assessed with gadolinium, as can response to fasciotomy

●● severe vascular compromise results in loss of normal muscle enhancement, with fascial enhancement and delayed centripetal enhancement from the fascial planes into the muscles

●● CECS: may be assessed with pre-and post-exercise MRI: ● change of muscle SI between pre-and post-exercise MRI is significantly greater in muscle

compartments with post-exercise hypertension ● the increased T2W SI in a muscle (Figs 8.110c, d) during or following recent activity does not recur

following fasciotomy323 ● a 1.54:1 ratio of increased T2W SI in the first recovery phase vs pre-exercise T2W SI baseline has

a sensitivity of 96%, specificity of 90% and an accuracy of 96% in the diagnosis of CECS324 ●● MRI findings are not specific for compartment syndrome, with similar features being present in muscle

strain, DOMS, DVT, cellulitis and lymphoedema

●● MO: is a particular type of muscle injury which results in progressive muscle ossification and may follow acute muscle trauma (post-traumatic MO; PTMO), burns and immobilisation/paraplegia

swelling and progressive loss of muscle function, with a history of trauma only obtained in ~50% of cases ●● 3 stages are described:

●● stage 1: acute/post-inflammatory ●● stage 2: subacute/post-tumoural stage ●● stage 3: chronic healing stage

●● non-specific areas of muscle inflammation are seen in stages 1 and 2, while peripheral lamellated bone develops in stage 3

●● MRI findings: ●● depend upon the age of the lesion, although some lesions may appear as non-specific soft-tissue masses ●● acute MO: shows predominantly muscle enlargement and oedema, appearing isointense on T1W images

(Fig. 8.111a) and hyperintense on T2W/STIR (Fig. 8.111b) images, with associated mass effect and diffuse or peripheral enhancement

●● subacute MO: a characteristic feature is the ring-like pattern of low SI (Fig. 8.111c) with central intermediate/ high SI (Fig. 8.111d) corresponding to the zonal peripheral calcification seen on CT (Fig. 8.111e):

● focal areas of T2W hypointensity may be present within the lesion, corresponding to calcification ● fluid-fluid levels are a recognised feature (Fig. 8.111f) and adjacent periostitis (Fig. 8.111g), reactive joint

effusions and marrow oedema may also be seen in the acute and subacute phases, decreasing with time ● rim or more diffuse enhancement is demonstrated following contrast

●● chronic lesions: show peripheral hypointensity due to cortical bone and mixed internal SI, which may include fatty SI due to mature trabecular bone (Fig. 8.111h):

● mature lesions lack periosteal oedema, an important marker for inactivity and an indication that surgical excision may be considered

Neurogenic Heterotopic Ossification (NHO) ●● NHO: is a frequent complication of spinal cord injury, occurring in >20% of all patients, being more

common in cases of traumatic than non-traumatic paralysis, and in young male adults:327,328 ●● it always occurs below the level of cord injury, with soft tissues around the hip most frequently involved

●● pelvic heterotopic ossification:326 in paraplegia results in imaging findings similar to PTMO ●● MRI findings:

●● poorly-defined areas of muscle SI abnormality, which vary depending upon the stage of ossification (immature versus mature):

● in the early stages, the features are those of muscle inflammation, with intermediate/increased SI on T1W/PDW FSE images (Fig. 8.112a), hyperintensity on T2W/STIR images (Fig. 8.112b) and variable contrast enhancement

● areas of reduced SI may be seen (Fig. 8.112a) due to developing muscle ossification (Fig. 8.112c) ● mature lesions have the features of corticated medullary bone (Figs 8.112d, e) ● heterotopic ossification: following thermal burns has similar imaging features to NHO, with

heterotopic ossification due to a combination of prolonged immobilisation as much as the injury

●● FOP, also known as myositis ossificans progressiva, is a rare disorder involving swelling and eventual ossification of ligaments, tendons and skeletal muscle

●● most cases are the result of new mutations, but an autosomal dominant pattern of inheritance with variable expression and penetrance is also recognised

●● clinically: it usually presents in childhood with symptoms of soft-tissue swelling, oedema and erythema initially occurring in the neck and progressing to soft-tissue ossification over time: ●● torticollis secondary to sternocleidomastoid involvement is the most common presentation

●● the soft-tissue calcification progresses in a cranial-to-caudal direction, with erratic flare-ups, the most rapid progression occurring in the second decade of life

●● ossified sheets eventually replace muscles and fascial planes, spanning joints and fusing with the skeleton, resulting in reduced or absent movement across affected joints

●● MRI findings: ●● early stages: T1W isointense and T2W hyperintense soft-tissue masses displacing fascial planes, with

surrounding oedema

●● maturing lesions: demonstrate decreasing T2W hyperintensity over time, with areas of T1W and T2W hypointensity developing as the lesion calcifies, while mature lesions may contain marrow SI (Figs 8.113a-c)

●● the spread of FOP along fascial planes is a helpful diagnostic feature, as is associated bilateral macrodactyly, hallux valgus and phalangeal synostosis involving the hallux or thumb, present at birth

●● muscle hernia: refers to a protrusion of muscle through a focal fascial defect, the latter most commonly occurring due to muscle hypertrophy and increased intracompartmental pressure

●● herniation tends to occur through relatively weak areas in the fascia, such as those traversed by blood vessels and nerves, and may be secondary to overuse or muscle hypertrophy

●● less commonly, hernias may occur through traumatic fascial defects ●● sites include the middle and lower leg, most commonly the tibialis anterior muscle, although involvement of

extensor digitorum longus, peroneus brevis/longus (at the site of exit of the superficial peroneal nerve from the lateral compartment), and gastrocnemius are also described, while involvement of the thigh and forearm is rare

●● muscle hernias: may be multiple and bilateral, and may complicate chronic exertional compartment syndrome

●● clinically: patients present with a small superficial soft-tissue mass, which becomes larger and firmer with muscle contraction: ●● rarely, they may be associated with substantial pain, cramp and tenderness ●● muscle hernias may become incarcerated or result in nerve entrapment, e.g. gastrocnemius herniation may

result in peroneal nerve entrapment, presenting as sciatica ●● MRI findings:

●● generalised outward bulging of the muscle with mild peripheral irregularity of contour ●● focal protrusion of muscle through the fascia (Figs 8.114a, b), which may become more pronounced

during dynamic imaging ●● in uncomplicated cases, muscle SI is normal, while symptomatic hernias may show increased T2W SI

●● pyomyositis: is an acute skeletal muscle infection that is usually caused by S. aureus (~90%), and less commonly by streptococci and Gram negative organisms

●● primary pyomyositis: has no definite cause but may result from haematogenous spread from a distant source ●● secondary pyomyositis: is due to direct extension from an infected site such as penetrating trauma,

gastrointestinal tract infections or malignancy

●● pyogenic pyomyositis: classically occurs in tropical countries, but also in the USA and Europe, usually complicating conditions such as DM, malignancy and AIDS: ●● 25-50% of patients report preceding blunt trauma334 ●● muscle infection is usually due to haematogenous spread and manifests as multiple small abscesses, usually

involving the lower limbs, particularly the hip and thigh regions ●● clinically: patients present with a subacute onset of fever, pain and muscle swelling, followed after 1-3 weeks

by painful induration of the muscle and diffuse swelling ●● TB pyomyositis:335 is rare and runs an indolent clinical course:

●● TB lymphadenitis: typically affects the neck but may rarely present as a soft-tissue mass in the limbs ●● MRI findings:

●● on T1W images, the muscle is mildly hyperintense with a rim of increased SI seen at the periphery ●● muscle oedema (stage 1) with increased T2W FSE/STIR SI, within which small foci of homogeneously

increased SI may develop, corresponding to fluid collections (stage 2), which typically have a thin hypointense, enhancing rim

●● FS T2W sequences demonstrate oedema better than FS post-contrast T1W sequences, but the latter is more sensitive in differentiating between muscle oedema and abscess formation336

●● associated features: include thickening of the fascial planes with reticulation of the subcutaneous fat and adjacent marrow oedema

●● in the clinical setting of diabetes, pyomyositis must be differentiated from diabetic muscle necrosis ●● the changes in viscosity that occur during abscess maturation and variability of protein content in abscesses

limits the utility of DWI sequences337 ●● TB pyomyositis:338 presents as an intramuscular mass, which is slightly hypointense on T1W images and

hyperintense on T2W images with central abscess formation: ● a peripheral slightly T1W hyperintense (Fig. 8.115a) and T2W hypointense rim is seen

(Fig. 8.115b, c), which enhances following contrast ● minimal or absent surrounding muscle oedema is typical, a helpful feature in differentiating

tuberculous from pyogenic pyomyositis ●● TB lymphadenitis: enlargement of lymph nodes, which may fungate through the skin to form a sinus

(Figs 8.115d, e)

●● muscle abscess: may arise from a variety of sources, including direct inoculation by a puncture wound, foreign body, haematogenous spread from a distant primary focus or spread from adjacent osteomyelitis/septic arthritis

●● pathologically: in the acute phase before liquefaction, it may be referred to as a phlegmon, which represents an infective myositis: ●● with time, the inflamed tissue is walled off and central necrosis occurs, producing an abscess, which in

the acute/subacute stage may have a very vascular wall ●● MRI findings:

●● T1W images demonstrate variable SI, which may range from hypointense to subtle muscle hyperintensity (Fig. 8.116a) while T2W FSE/STIR images show very high central SI with a peripheral hypointense rim (Fig. 8.116b)

●● the abscess wall is thin and hyperintense and enhances following contrast (Fig. 8.116c) ●● air within an abscess can result in the presence of an air-fluid level, and dystrophic calcification may be

seen in the wall of a chronic abscess ●● associated features: varying degrees of surrounding muscle oedema are commonly seen (Fig. 8.116b):

● reactive BMO, which in itself is not indicative of OM, may also occur (Fig. 8.116c) ● subcutaneous oedema and a reticular pattern in the subcutaneous fat

●● necrotising fasciitis: is a relatively rare, but often fatal condition producing extensive necrosis of subcutaneous tissues, fascia and adjacent soft-tissue structures, most commonly involving the extremities, perineum and trunk

●● it may be polymicrobial or monomicrobial, and falls under the heading of necrotising soft-tissue infections, that includes necrotising cellulitis

●● clinically: an underlying predisposing condition (e.g. leukaemia, AIDS, chronic renal failure, diabetes, immune suppression, obesity, intravenous drug use) is commonly present, and it often follows a trivial injury: ●● patients present with a short period of symptoms, which may rapidly progress to septic shock and death if

untreated ●● overall mortality rates of up to 73% are reported, which can be reduced to 10% with aggressive early

management ●● the condition must be differentiated from cellulitis, since necrotising fasciitis requires surgical

debridement and extensive fasciotomy in addition to antibiotic therapy ●● pathologically: initially the superficial tissues are affected, but disruption of the deep fascia may result in

muscle necrosis, and progression to compartment syndrome further threatens compartmental soft-tissue viability

●● MRI findings: ●● soft-tissue thickening and tracking of high SI fluid along the deep fascial planes is evident on T2W images ●● a pattern similar to cellulitis is seen in the subcutaneous tissues, while soft-tissue gas formation appears as

small foci of signal void, best seen on GRE sequences, although not a universal finding ●● oedema may be seen in the muscle adjacent to the affected fascia ●● areas of T2W hyperintensity show enhancement on post-contrast T1W images, unless extensive tissue

necrosis has occurred, in which case marginal enhancement may be seen ●● fascial thickening and hyperintensity on T2W images are also features of non-infective eosinophilic

fasciitis341

●● cellulitis: is the commonest form of soft-tissue bacterial infection, which may remain localised or extend rapidly to form a soft-tissue abscess

●● superficial fasciitis: is commonly associated with cellulitis and is treated conservatively, in contrast to necrotising fasciitis

●● MRI findings: ●● thickening of the involved skin, subcutaneous septa and underlying fascia, similar to that seen with a deep abscess ●● these structures appear hyperintense on T2W images and enhance following contrast ●● surrounding soft-tissue oedema of variable degree is common

●● echinococcosis: cystic echinococcosis or hydatid disease is caused by E. granulosus and mainly affects the liver and lungs

●● musculoskeletal infection: occurs in 1-4% of cases with the pelvis, spine and limbs being typically affected ●● the condition is most commonly seen in rural sheep-raising regions, such as the Mediterranean,

South America and Australia ●● musculoskeletal lesions are slow-growing, and most patients with musculoskeletal involvement present in adulthood ●● primary muscle involvement is rare due to the high levels of lactic acid, but the muscles most commonly

affected include the paravertebral, gluteal and lower limb muscles ●● MRI findings:

●● a multi-locular muscle mass with endovesical daughter cysts is classical (cyst within a cyst) ●● the cysts demonstrate variable SI compared to skeletal muscle on T1W images (Fig. 8.117a), while on

T2W/STIR images, the cysts are uniformly hyperintense and the cyst walls are hypointense (Fig. 8.117b): ● daughter cysts may have differing SI to those of the mother cysts (Fig. 8.117c)

●● the cyst wall is double layered, comprising a T2 hypointense inner layer consisting of the acellular ectocyst, and a T2 hyperintense outer layer representing the vascularised pericyst

●● separation of the laminated membrane and the pericyst gives rise to the ‘water lily’ sign, with the collapsed cyst membrane lying in the most dependent part of the mother cyst (Fig. 8.117a)343

●● gravity-dependent levels within the cyst represent hydatid sand, consisting of floating capsules and scolices ●● following contrast, rim-enhancement of the cyst may be seen

●● soft-tissue masses: the vast majority are benign, with an estimated annual incidence of 300/100,000 population

●● benign soft-tissue tumours: are ~100× more common than soft-tissue sarcoma (STS), while STS represent 0.7% of all adult malignant tumours

●● clinically: features that suggest that a soft-tissue mass may be malignant include: ●● a history of pain and/or rapid growth with an older age of presentation ●● a mass which is deep to the fascia and which is over 5 cm in dimension

●● the role of MRI in the assessment of a potential soft-tissue mass includes: ●● the demonstration or exclusion of an actual lesion or a pseudomass ●● the precise location (intramuscular, extramuscular, superficial, deep) ●● local staging, related to compartment and adjacent neurovascular structures ●● characterisation of a variety of non-neoplastic, benign neoplastic and some malignant lesions, precluding

the need for biopsy ●● MRI findings:

●● the majority of intermediate/high-grade STS have no specific imaging features ●● they typically grow in a centrifugal fashion until resistance is met, usually in the form of fascial boundaries

in which case they will follow the path of least resistance, which is in a longitudinal direction within the compartment:

● therefore, STS are usually intracompartmental, and round or oval in shape ●● STS are typically isointense to muscle on T1W images (Fig. 8.118a) and heterogeneous on PDW/T2W

images (Fig. 8.118b) (in ~90% of cases) with intermediate/mild increased SI and heterogeneous increased SI on FS T2W/STIR sequences (Fig. 8.118c):

● a change in SI pattern from homogeneous T1W to heterogeneous T2W is reported in 78-84% of STS

●● the typical morphology of a STS is a large (>5 cm in 85% of cases), well-defined (due to formation of a pseudocapsule), mass located deep to the fascia, with lobular internal architecture separated by ill-defined fibrous septa (53-75% of cases) (Figs 8.118d, e):

● only 5% of benign soft-tissue tumours exceed 5 cm in dimension and ~1% of benign soft-tissue tumours arise deep to the fascia

● lesion size <3 cm has a PPV for benignity of 88%, while a diameter of >5 cm predicts a malignant mass with sensitivity of 74%, specificity of 59% and accuracy of 66%

●● using a combination of the following signs, malignancy can be predicted with a sensitivity and specificity of 81%:

● absence of low SI on T2W images, inhomogeneous SI on T1W images and a mean lesion diameter of >33 mm ● the most sensitive features of malignancy are high T2W SI, inhomogeneous T1W SI and size >33 mm ● the most specific features of malignancy are the presence of necrosis, bone or neurovascular

involvement, and mean diameter of >66 mm ●● the relationship of subcutaneous tumours to the adjacent fascia may also give a clue as to their

aggressiveness,349 although extension through the deep fascia is not a universal indicator of malignancy in superficial soft-tissue masses:348

● subcutaneous lesions that cross the fascia (Fig. 8.118f) and have an obtuse angle between the margins of the mass and the fascia are 6-7× more likely to be malignant than lesions that have an acute angle with the fascia

●● peritumoural oedema is not a striking feature of primary STS, but may be seen with soft-tissue lymphoma or metastasis

●● variations in SI: T2W SI similar to fluid is suggestive of either extensive tumour necrosis (Fig. 8.119a), a major myxoid component (Fig. 8.119b) or a cartilaginous lesion (see later):

● diffuse reduction of T1W SI compared to muscle is seen with myxoid tumours (Fig. 8.119c) while focal reduced T1W SI may be due to necrosis (Fig. 8.119d)

● poorly-defined areas of mildly increased T1W SI are consistent with the presence of subacute haemorrhage (Fig. 8.119d)

● diffuse mild increased T1W SI has also been recognised in some sarcomas (Fig. 8.119e) ●● cyst-like lesions:350 certain tumours appear at MRI as cystic lesions, with reduced T1W SI compared to

muscle (Fig. 8.119c) and marked hyperintensity on T2W (Fig. 8.119b) and STIR images (Fig. 8.119f): ● such lesions may be non-neoplastic (e.g. ganglion/synovial cysts), benign neoplasms (e.g. soft-tissue

myxoma) or malignant neoplasms (e.g. myxoid soft-tissue sarcoma)

● features that are suggestive of a malignant lesion are: – a larger mean dimension: benign 4.3 cm versus malignant 7.3 cm – a larger greatest dimension: benign 6 cm versus malignant 8 cm – heterogeneity of the lesion on T1W images

●● local staging, including involvement of the adjacent bone (Fig. 8.120a), extracompartmental extension (Fig. 8.120b), neurovascular bundle encasement (Fig. 8.120c) and skin involvement (Fig. 8.120d) are uncommon features that are relatively specific for malignancy, but are insensitive:

● however, vascular encasement is also seen with fibromatosis and bone erosion with PVNS ●● enhancement is not of value for the routine assessment of STS but may help in the differentiation of

a complex subacute/chronic haematoma from an extensively haemorrhagic sarcoma (Figs 8.120e, f ) ●● dynamic gadolinium-enhanced MRI may be of value in differentiating benign from malignant lesions:

● on time-intensity plots, benign tumours always show a SI increase that is <100%, whereas that for malignant lesions is between 80% and 280%

● slopes with >30% increase in SI/min are seen in 84% of malignant tumours, while slopes with <30% increase in SI/min are seen in 72% of benign tumours: – this criterion may not differentiate malignant tumours with extensive necrosis

● malignant tumours demonstrate increased neovascularity at their periphery and increased interstitial pressure centrally, which may result in differential rim-centre enhancement patterns, with most malignant tumours demonstrating early peripheral enhancement

●● DWI: shows promise in the evaluation soft-tissue tumours, but suffers from a lack of specificity, with a significant overlap in appearances of some benign and malignant lesions:

● restriction of diffusion may also occur in haematomas, abscesses and soft-tissue tumours, but DWI has the benefit of sensitive visualisation of lymph nodes351

●● the current classification system for ST tumours is based on the World Health Organisation (WHO) classification established in 2013

●● histological types include: adipocytic tumours, fibroblastic/myofibroblastic tumours, fibrohistiocytic tumours, smooth muscle tumours, pericystic (perivascular) tumours, skeletal muscle tumours, vascular tumours, gastrointestinal stromal tumours, chondro-osseous tumours, neurogenic and nerve sheath tumours and tumours of uncertain differentiation, and undifferentiated/unclassified tumours

●● each group may be divided into 4 categories: benign, intermediate (locally aggressive), intermediate (rarely metastasising) and malignant

●● benign adipocytic tumours:355 include lipoma, lipomatosis, lipomatosis of nerve, lipoblastoma/ lipoblastomatosis, angiolipoma, myolipoma of soft tissue, chondroid lipoma, spindle cell/pleomorphic lipoma and hibernoma

●● intermediate (locally aggressive) adipocytic tumours: include atypical lipomatous tumour (ALT; previously well-differentiated liposarcoma)

●● malignant adipocytic tumours: include dedifferentiated liposarcoma, myxoid liposarcoma, pleomorphic liposarcoma and mixed-type liposarcoma

●● the WHO classification replaced the term ‘round cell liposarcoma’ by ‘high-grade myxoid liposarcoma’, as not all of these tumours have a round cell morphology353

●● lipoma: is the commonest soft-tissue tumour accounting for 50% of cases, with a reported prevalence of 2.1/100 people, and usually presenting in the 5th-7th decades

●● lipomas: may be classified as superficial (very common) or deep, and are multiple in 5-15% of cases

●● superficial lesions: arise in the subcutaneous fat and are frequently difficult to distinguish from the surrounding subcutaneous fat, most commonly involving the upper back, neck, proximal extremities (especially the shoulder), and abdomen

●● deep lipomas: may be subclassified as intramuscular or intermuscular, with those affecting the extremities most commonly being intramuscular: ●● when deep lesions affect both the intra-and intermuscular spaces, they are referred to as infiltrating lipomas ●● deep lipomas most commonly affect the lower limb (45%), trunk (17%), shoulder (12%) and upper limb

(10%) and may reach 20 cm in size by the time of presentation ●● 80% of lipomas measure less than 5 cm in size

●● clinically: lipomas typically present as painless masses but may be symptomatic in ~25% of cases, producing local pain/tenderness, limitation of motion and nerve compression

●● pathologically: lipomas are composed of mature adipocytes and fibrous connective tissue septa: ●● if prominent, non-septal fibrous components are present, the term fibrolipoma is used

●● MRI findings: ●● classical lipomas appear as homogeneous fatty masses in 11-22% of cases, being hyperintense on T1W/

T2W images (Figs 8.121a, b) and hypointense on FS/STIR/T2W GRE images (Fig. 8.121c) ●● thin (<2 mm) internal septa are demonstrated in 37-49% of cases (Fig. 8.121d) ●● the fatty component shows no enhancement following contrast, while the septa show no enhancement in

58% and moderate enhancement in 37% of cases359 ●● a more complex appearance, including thick septa (>2 mm) and nodular non-lipomatous areas is reported

in ~30% of cases, which may be due to fibrous tissue or areas of fat necrosis, and such lesions cannot be confidently differentiated from ALT

●● additional features: areas of mineralisation/ossification (Figs 8.121e, f ) are rare and more common with liposarcoma:

● superficial lesions commonly show a hypointense fibrous capsule (Fig. 8.121d), which may enhance ● intramuscular lipomas may show an irregular margin and interdigitation with the adjacent muscle

(Fig. 8.121g), a feature not described with liposarcoma ● subcutaneous lipomas may also not show a fibrous capsule, when they are referred to as non-

encapsulated lipomas (Fig. 8.121h)

●● lipomatosis: represents a diffuse overgrowth of mature lipomatous tissue and subtypes involving the musculoskeletal system include: ●● multiple symmetric lipomatosis: also termed Madelung disease or Launois-Bensaude syndrome:

● almost exclusively affects middle-aged men with a history of alcoholism (60-90% of cases) and results in a painless, progressive deposition of fat around the neck, upper trunk, arms, cheeks and axilla

● lipomatosis has also been rarely described in children under 2 years of age ● sensorimotor neuropathy is present in 59-84% of cases and CNS involvement occurs in 50%

●● shoulder girdle lipomatosis: results in gradual progressive unilateral enlargement of the shoulder and upper arm due to lipomatous infiltration between the muscles of the upper extremity and chest wall, commonly with associated myoneuropathy

●● macrodactyly is a recognised feature of lipomatosis, but when extremities are involved, the most distal portions of the limbs are often spared

●● adiposis dolorosa: also known as Dercum’s disease, is characterised by multiple subcutaneous lipomas associated with pain and tenderness, typically affecting obese, post-menopausal women:

● lipomas most commonly occur around the pelvic girdle, hips, thighs and knees ●● MRI findings:

●● multiple symmetric lipomatosis: multiple subcutaneous and deep fatty masses (particularly between the sternomastoid, trapezius and paraspinal muscles), with occasional mediastinal extension that may cause tracheal compression

●● shoulder girdle lipomatosis: diffuse mature fatty infiltration of the subcutaneous tissues ●● adiposis dolorosa: multiple oblong superficial subcutaneous fatty masses, usually <2 cm, best seen as areas

of nodular or ‘blush-like’ increased SI on FS PDW/T2W/STIR sequences, poorly visualised on T1W sequences and without contrast enhancement360

●● lipomatosis of nerve: is also referred to as fibrolipomatous hamartoma of nerve, perineural lipoma, intraneural lipoma and neural fibrolipoma, and is the result of epineurial proliferation of fibroblasts and mature fat cells

●● it most commonly presents in early childhood and the upper limb is affected in 78-96% of cases, most commonly the median nerve (85% of cases), followed by the ulnar nerve

●● involvement of the lower limb, radial nerve, brachial plexus and cranial nerves is also reported ●● clinically: patients present with a slowly growing mass at the wrist, hand or forearm:

●● growth is most rapid during childhood and affects the cross-sectional area and longitudinal extent of the lesion, with osseous growth ceasing by mid-adulthood

●● pain and neurological symptoms, such as carpal tunnel syndrome may occur ●● nerve territory oriented macrodactyly is reported in 27-67% of cases (more commonly occurring in

women and involving the upper extremity), then being referred to as macrodystrophia lipomatosa ●● pathologically: the affected nerve is diffusely enlarged by fibro-fatty tissue, which separates the intact nerve

fibres ●● MRI findings:

●● longitudinally orientated hypointense linear strands (nerve fascicles) within a diffusely thickened nerve due to excessive lipomatous tissue (Figs 8.122a-c)

●● the thickened nerve fascicles are evenly dispersed throughout the enlarged nerve and are surrounded by fat, giving a ‘spaghetti-like’ appearance on coronal sequences

●● the fatty tissue is divided by thin septa, resulting in a ‘lotus’-like appearance on axial imaging ●● increased fat content of the digit is also seen with associated macrodystrophia

●● lipoblastoma: is a benign, circumscribed tumour of embryonal white fat that occurs in infancy and early childhood (median age 1 year old, with most children aged under 3 years), boys are affected 2-3 times more frequently than girls: ●● the term benign lipoblastomatosis is used to refer to a diffusely infiltrating lesion

●● lipoblastoma: is more common (70% of cases) and occurs in the subcutaneous tissues, while lipoblastomatosis is a more diffuse process and involves both the subcutaneous tissues and the underlying muscle

●● the extremities are most commonly involved, followed by the trunk and neck ●● lipoblastomas eventually evolve into lipomas ●● MRI findings:

●● lipoblastomas: most lesions are ~5 cm in size, being well-defined and lobular with internal septa and fat SI on all pulse sequences (Figs 8.123a, b), though slightly hypointense to subcutaneous fat on T1W:

● in younger children, prominent areas of myxoid change may be present, appearing as intermediate SI on T1W (Fig. 8.123c), hyperintensity on T2W/STIR (Fig. 8.123d) and showing enhancement following contrast

● cystic change has also been described and post-contrast imaging reveals variable enhancement patterns, or may show no enhancement

●● lipoblastomatosis: has similar appearances but demonstrates infiltrative growth, involving both the superficial tissues and underlying muscle

●● angiolipoma: is a rare benign subcutaneous lesion usually seen in males in the 2nd-3rd decades of life, and most commonly involving the forearm, trunk and upper arm

●● lesions are multiple in approximately 70% of cases ●● clinically: angiolipoma presents as small (<2 cm) tender subcutaneous masses ●● MRI findings:

●● small, encapsulated subcutaneous lesions with SI characteristics of fat on all pulse sequences (Figs 8.124a-c) ●● they may contain areas of intermediate T1W and increased T2W/STIR SI, which enhance following

contrast and represent the vascular component of the lesion (Figs 8.124a-c)

●● myolipoma: is an extremely rare, benign lipomatous lesion, most commonly seen in females (2:1 ratio) in the 5th-6th decades of life

●● it usually involves the retroperitoneum or abdominal cavity, but may also be found in the groin, trunk, orbit, mediastinum or extremities

●● deep lesions are typically 10-25 cm in size at time of presentation, while superficial lesions present much earlier as painless soft-tissue masses

●● MRI findings: ●● lesions have predominantly fat SI on all pulse sequences with a variable amount of non-adipose tissue due

to the presence of associated smooth muscle, which appears of intermediate SI on T1W and T2W images ●● large lesions may contain calcification, appearing as areas of signal void

Chondroid Lipoma365 ●● chondroid lipoma: is a rare benign fatty lesion which presents as a slowly growing mass, and may arise in the

subcutaneous fat, the deep fascia, or within or between the muscles: ●● intraneural chondroid lipoma has been reported, but is extremely rare366

●● females are affected 4× more commonly than males and the age at presentation ranges from 14 to 70 years, most commonly presenting in the 3rd and 4th decades

●● the commonest sites of involvement include the proximal extremities and limb girdles ●● pathologically: the lesion is composed of variable amounts of mature fat, lipoblasts and myxoid chondroid

matrix ●● the heterogeneous radiological and pathological appearances can bear a close resemblance to myxoid

liposarcoma or myxoid chondrosarcoma in the limbs or trunk, and pleomorphic adenoma in head and neck lesions367

●● MRI findings: ●● lesions vary in size from 1 to 11 cm at presentation and the SI characteristics depend upon the proportion

of different tissues (Figs 8.125a, b), and in the absence of much mature fat, the lesion may appear as a predominantly cystic mass due to a high myxoid content

●● spindle cell lipoma/pleomorphic lipoma: are similar conditions that typically occur in men (~90%) and present in the 40-70 year age range

●● the male predominance is thought to be related to the expression of androgen receptors by the tumour ●● approximately 60% of cases affect the subcutaneous tissues of the posterior neck (Fig. 8.126a), shoulder and

back (Fig. 8.126b)

●● intramuscular extension may be seen, and in these cases traversing muscle fibres result in a striated appearance not seen in other lipomata371

●● deep lesions and lesions affecting the extremities are uncommon, as are multiple lesions ●● the majority of lesions are 3-5 cm in dimension, but may reach almost 30 cm ●● MRI findings:

●● mature fat, ranging from 25% to 75% of the lesion volume is seen in 35-78% of cases (Figs 8.126a, b), with lesions devoid of fat signal occasionally encountered

●● the spindle cell component has intermediate SI on T1W images and is either isointense or hyperintense to fat on T2W or STIR sequences, the non-adipose tissue enhancing following contrast

●● the MR evaluation of adipose to non-adipose content correlates with the histological grading of the lesions in 86%370

●● hibernoma: is a rare benign tumour composed of brown fat, which typically presents as a painless soft-tissue mass and may feel warm due to the associated hypervascularity of the tumour

●● the lesion is most commonly identified in the thigh (~30% of cases), although many sites have been reported, with ~60% presenting in the 3rd-4th decades of life

●● it is usually 5-10 cm in dimension and may occur in an intermuscular, intramuscular or subcutaneous location

●● pathologically: the lesion is composed of a mixture of brown and white fat and therefore, the MRI signal characteristics will depend upon this ratio, with ~80% of cases composed primarily of brown fat and 7% containing significant amounts of adult fat

●● MRI findings: ●● typical hibernoma: is composed of tissue, which is slightly hypointense compared to adult fat on T1W/

PDW/T2W images (Figs 8.127a-c) and shows mild hyperintensity on FS T2W FSE /STIR images ●● multiple linear areas of intermediate T1W and hyperintense T2W/STIR SI are seen due to vessels

(Figs 8.127a, b), which enhance following contrast ●● lesions containing predominantly white fat have SI characteristics that are those of adult fat, but the

presence of multiple internal vessel is suggestive of the diagnosis (Figs 8.127d, e)

●● ALT: was previously termed well differentiated liposarcoma and is the commonest soft-tissue liposarcoma, accounting for ~50% of cases

●● the lesion most commonly presents in the 6th-7th decades of life, with equal sex distribution ●● the commonest site is the deep soft tissues of the extremities (65-75% of cases), with ~50% involving

the lower limb, particularly the thigh ●● the upper limb is involved in 14% of cases, the trunk in 12% and the remainder located in the

retroperitoneum and head/neck region

●● the majority are intramuscular, and less commonly intermuscular or subcutaneous, the latter being referred to as atypical lipomas

●● clinically: the tumour typically presents as a painless mass, with pain and tenderness reported in only 10-15% of cases: ●● differentiation from lipoma can be difficult and features favouring a diagnosis of ALT include: male sex

(odds ratio; OR: 3), age >66 years (OR: 6), <75% fat (OR: 8.3), presence of calcification, size >10 cm (OR: 14.2), thick septa (OR: 4.9), non-lipomatous globular/nodular areas (OR: 2.3), measuring over 1 cm in size, and location in the lower limb

●● there is also a recognised overlap between the imaging features of lipoma and ALT, and a positive MDM2 and/or CDK4 amplification status on molecular pathology is more reliable than imaging in such cases376,377

●● imaging features are of a predominantly fatty mass containing some non-lipomatous components ●● generally, >75% of the lesion contains mature adult fat, which appears isointense to subcutaneous fat on all

pulse sequences (Figs 8.128a-c) ●● the non-lipomatous components are typically in the form of thick fibrovascular septa (>2 mm) that may

show some nodularity (Fig. 8.128d) and enhance following contrast ●● focal nodular or globular non-fatty areas may also be seen, but are typically less than 2 cm in size

(Figs 8.128e, f ) ●● areas of signal void may occur due to the presence of metaplastic ossification (Fig. 8.128g)

●● dedifferentiated liposarcoma (dd-liposarcoma): represents a biphasic tumour, with one component being an ALT and the other being a high-grade non-lipomatous sarcoma

●● dedifferentiation occurs in ~10% of all liposarcomas, most commonly in deep-seated lesions, particularly those in the retroperitoneum, and usually presents in the 7th decade of life

●● of all dd-liposarcomas, ~4.5% affect the upper limb and 24% occur in the lower limb, while dedifferentiation of superficial lesions is extremely rare (<1%)

●● the estimated risk of dedifferentiation for deep extremity lesions is ~5% and occurs de novo in 90% of cases ●● the dedifferentiated tumour is either a high-grade fibrosarcoma/pleomorphic spindle cell sarcoma in 90% of

cases, while association with osteosarcoma has also been reported ●● distant metastases are reported in 15-20% of cases, usually to the liver and lungs and occasionally to the peritoneum ●● MRI findings:

●● imaging essentially shows the features of an ALT and dedifferentiation manifests as areas of focal, nodular non-lipomatous tissue measuring >1 cm in diameter, although it is usually >3 cm at presentation

●● occasionally, the dd-component may form the majority of the lesion, typically showing intermediate SI on T1W images (Fig. 8.129a) and intermediate/high SI on T2W images, showing failure to suppress on FS T2W FSE/STIR images (Figs 8.129b, c)

●● enhancement of the high-grade component is seen following contrast

●● myxoid liposarcoma: is the 2nd commonest type of liposarcoma, accounting for 20-50% of all liposarcomas and 10% of all STS

●● it now encompasses a group of high-grade tumours which were previously designated as round-cell liposarcoma, and have a poorer prognosis

●● patients typically present in the 4th-5th decades and myxoid liposarcoma is the commonest type of liposarcoma in children, accounting for 76% of all liposarcomatous tumours in the 11-16 year age range

●● extremity myxoid liposarcomas: are typically subfascial/intermuscular lesions (70-80% of cases), with up to 90% affecting the lower limb, particularly the medial thigh and popliteal fossa

●● the groin, buttock and calf are also affected, while 5% of lesions arise in the upper limb ●● low-grade and high-grade tumours are usually confined to a single anatomical compartment at presentation ●● large vessel encasement and bone infiltration is seen more frequently in higher grade tumours, occurring in

up to 55% and 18% of cases respectively379

●● clinically: they present as painless masses, which may reach up to 15 cm in size: ●● low-grade myxoid liposarcoma: tends to be smaller at presentation than high-grade lesions and is considered

a low-grade tumour with a lower risk of metastasis ●● a greater round-cell component (>5%) and the presence of tumour necrosis are considered to be unfavourable

prognostic factors ●● MRI findings:

●● typically appear as large, well-defined lobular intermuscular lesions, with the myxoid stroma resulting in intermediate/low T1W SI (Fig. 8.130a) and marked T2W/STIR hyperintensity (Figs 8.130b, c)

●● intralesional haemorrhage and necrosis may be present ●● a capsule is seen in 37% of cases, and when present is suggestive of a low-grade lesion ●● the pathognomonic feature is the presence of fatty tissue seen within the mass in ~50-90% of cases, which

comprises 10% of low-grade lesions and 6% of high-grade lesions, and is typically contained within septa manifesting as linear regions (Fig. 8.130d) or small nodules (Fig. 8.130a) of T1W hyperintensity

●● in the absence of tumour fat, the lesion may resemble a cyst, with homogeneous low T1W SI and increased T2W SI (~10% of cases)

●● following contrast, the lesion shows enhancement, which may be peripheral nodular (61% of cases) (Fig. 8.130e), central nodular (41% of cases) or diffuse (17% of cases) (Fig. 8.130f)

●● the presence of a significant round cell component results in well-defined areas of intermediate T1W and T2W SI, which may be indistinguishable from dd-liposarcoma

●● pleomorphic liposarcoma: is the least common subtype of liposarcoma, accounting for 5-15% of cases and 20% of all pleomorphic STSs

●● the tumour usually presents after the age of 50 years and is typically intramuscular, involving the lower limb in 56% of cases and the upper limb in 20% of cases: ●● the remainder are found in non-musculoskeletal locations

●● the lesion contains small amounts of lipoblasts but little mature adipose tissue ●● MRI findings:

●● the tumour is typically well-defined and usually >10 cm at presentation ●● the majority of the lesion shows intermediate T1W SI (Fig. 8.131a) and intermediate/high PDW/T2W/

STIR SI (Fig. 8.131b) ●● haemorrhage and necrosis are common features and up to 75% of cases show small focal areas of fat, seen as

increased T1W SI (Fig. 8.131a) ●● fat and subacute haemorrhage both appear hyperintense on T1W images, but may be differentiated on FS T2W

FSE/STIR images, when the fatty component shows low SI and haemorrhage remains of increased SI

●● mixed-type liposarcoma: accounts for 5-12% of all liposarcomas and rarely affects the limbs ●● MRI: demonstrates a combination of the previously mentioned types of liposarcoma

●● benign fibroblastic/myofibroblastic tumours: include nodular fasciitis, proliferative fasciitis and proliferative myositis, myositis ossificans, myofibroma/myofibromatosis, fibromatosis colli, fibroma of tendon sheath, desmoplastic fibroblastoma, calcifying fibrous tumour, angiofibroma, angiomyofibroblastoma, Gardner fibroma and giant-cell angiofibroma

●● intermediate (locally aggressive) fibroblastic/myofibroblastic tumours: include superficial fibromatosis (plantar/palmar), desmoid-type fibromatosis and lipofibromatosis, giant-cell fibroblastoma

●● intermediate (rarely metastasising) fibroblastic/myofibroblastic tumours: include solitary fibrous tumour, myofibroblastic inflammatory tumour, myofibroblastic sarcoma and dermatofibrosarcoma protuberans

●● malignant fibroblastic/myofibroblastic tumours: include adult fibrosarcoma, myxofibrosarcoma and low-grade fibromyxoid sarcoma

reactive ●● inclusion of giant-cell fibroblastoma and dermatofibrosarcoma protuberans (DFSP), previously in the skin section ●● similarity between low-grade fibromyxoid sarcoma and sclerosing epithelioid fibrosarcoma, which share

the same gene rearrangement

●● nodular fasciitis: also known as nodular pseudosarcomatous fasciitis, is a benign soft-tissue tumour of uncertain aetiology, being the commonest lesion of fibrous origin

●● it is self-limiting and can occur at any age, although 85% of cases present before the age of 50 years, with most cases presenting between 20 and 40 years

●● the upper limb and shoulder girdle (79%) are the commonest sites of involvement, while the head and neck and the lower limb are affected less commonly: ●● rare reports exist of intraneural and epidural lesions383,384

●● the lesion may be subcutaneous (commonest) (Fig. 8.132a), intramuscular (Fig. 8.132b) or fascial/ intermuscular (Figs 8.132c-e) and rarely is intravascular or intradermal

●● clinically: nodular fasciitis presents as a rapidly growing mass, which is tender in 50% of cases: ●● neurological symptoms may occur with compression of peripheral nerves and a history of trauma is noted

in 10-15% of cases ●● rapid growth can mimic STS clinically, but the natural history of the lesion is spontaneous regression,

with a very low rate of recurrence after surgery ●● pathologically: lesions may be classified as myxoid, cellular or fibrous and calcification is rarely seen ●● MRI findings:

●● lesions are well-defined with a round or oval shape and typically ranging is size from 1 to 2.5 cm although rarely reaching 10 cm

●● the tumour is isointense or slightly hyperintense to muscle on T1W images (Figs 8.132b, c), intermediate SI on T2W sequences (Figs 8.132a, d) and of intermediate SI or hyperintense on FS T2W FSE images (Fig. 8.132e)

●● enhancement may be either uniform or heterogeneous, and lesions containing focal T2 hyperintensity, likely representing intralesional cystic change (Fig. 8.132e), show a lack of contrast enhancement in these areas

●● a fascial tail and perilesional oedema tracking along the fascial plane are variably seen ●● transcompartmental spread occurs in 30%, and lesions abutting bone may result in osseous remodelling

and saucerisation with associated marrow oedema ●● intra-articular extension of periarticular lesions is recognised, but primary intra-articular

involvement is rare385

●● elastofibroma dorsi (EFD): is a benign fibroblastic tumour of unknown aetiology, which has a reported prevalence of ~2%

●● 99% of cases arise in an infrascapular (77%) or subscapular (23%) location, usually overlying the 6th to 8th ribs, and are bilateral in up to 60% of cases (Fig. 8.133a)

●● less commonly reported sites for EFD include the elbow, shoulder, ischial tuberosity, foot and neck ●● pathologically: it is composed of hyalinised collagen with scattered fibroblasts and entrapped islands of mature

fatty tissue ●● clinically: EFD may be asymptomatic (>50% of cases) and found incidentally, may cause mild pain or scapular

snapping, or manifest as a slowly growing mass

●● the mean age at presentation is 70 years and the lesion is more common in females ●● MRI findings:

●● EFD appears as a poorly-defined mass adjacent to the posterolateral rib cage, deep to serratus anterior, subscapularis, rhomboids and latissimus dorsi (Fig. 8.133a)

●● the lesion is composed of multiple hypointense strands, which are arranged parallel to the chest wall and may range from 5 to 10 cm in dimension

●● the SI is similar to muscle on both T1W and T2W images, with intermingled areas of fat SI (Figs 8.133b, c)

●● mild increased SI may be seen on STIR (Fig. 8.133d) and the degree of enhancement is variable

●● proliferative fasciitis/proliferative myositis:389 represent benign mass-forming fibrous proliferations, which are regarded as variants of nodular fasciitis:

●● MRI findings: ●● a solid, mass-like lesion or a poorly-defined mass with associated oedema, usually involving

the extremities, particularly the forearm (Figs 8.134a, b) and thigh

●● proliferative myositis has similar precontrast imaging features to that of an inflammatory myopathy, but produces a ‘checkerboard’ pattern of contrast enhancement

●● contrast enhancement of thickened fascia is seen in proliferative fasciitis ●● fibromatosis colli:390 also termed sternocleidomastoid pseudotumour of infancy, is a benign fibrous mass

associated with torticollis (14-20% of cases) in neonates and infants, 75% of cases involving the right side of the neck: ●● it usually presents in the 2nd-4th week of life, typically being associated with a history of birth trauma/

difficult delivery (90% of cases) ●● MRI findings:

●● enlargement of the lower third of the muscle with variable signal characteristics, but typically isointense to muscle on T1W SE sequences and slightly hyperintense on T2W images, with a hypointense rim of muscle

●● fibroma of tendon sheath:391,392 is a lesion composed of tightly packed spindle cells surrounded by collagen fibres, which has similar clinical and imaging features to GCT of tendon sheath: ●● ~80% of cases involve the upper limb, usually the flexor surfaces of the wrist and hand (Figs 8.134c, d)

●● MRI findings: ●● a well-defined round/oval lesion typically measuring 1-2.5 cm in dimensions, with intermediate/low

SI on both T1W and T2W images, the SI determined by the extent of hyalinisation and number of proliferating fibroblasts (Figs 8.134e, f )

●● deep fibromatosis: is also termed extra-abdominal desmoid tumour or musculo-aponeurotic fibromatosis and is a lesion of intermediate aggressiveness showing local invasion and frequent recurrence, without metastases

●● the peak incidence of occurrence is between 25 and 35 years, with a female to male preponderance of 2:1 and ~70% of extra-abdominal cases involving the limbs

●● the shoulder (20%), chest wall and back (15%), thigh (12%), neck (10%) and knee (7%) are most commonly affected, and fibromatosis is the commonest soft-tissue mass involving the rectus abdominis

●● the majority of lesions are solitary but multi-focal synchronous lesions are seen in 10-15% of patients, in which case associated metaphyseal dysplasia similar to an Erlenmeyer flask deformity may occur

●● pathologically: fibromatosis demonstrates an infiltrative growth pattern and consists of fibroblasts surrounded by a variable amount of collagen, with areas of myxoid change, haemorrhage and inflammation occasionally seen

●● clinically: patients present with a hard, slowly growing mass, which may result in contractures from involvement of deep structures or neurological symptoms due to nerve entrapment

●● the majority of cases are idiopathic or sporadic, and the remainder associated with familial adenomatous polyposis (Gardner’s syndrome)

●● associations with pregnancy, oestrogen, radiotherapy, trauma and surgery are recognised ●● MRI findings:

●● fibromatosis is typically intermuscular, although muscle invasion is common (Figs 8.135a, b) and linear extension along fascial planes is a characteristic feature, the latter commonly extending for quite a distance from the primary lesion

●● an infiltrative margin is classically seen, though slightly less commonly the margin may be well-defined ●● the SI pattern depends upon the histological nature of the lesion, the lesion being typically isointense

to muscle on T1W images (Fig. 8.135a), and when particularly cellular is also mildly/moderately hyperintense on T2W/STIR images (Figs 8.135c, d), showing enhancement following contrast (Fig. 8.135e), with only 10% of lesions showing no enhancement

●● relatively hypocellular lesions show intermediate/low SI on T2W/STIR images ●● prominent bands of low SI tissue running through the lesion are seen on all pulse sequences due to

the presence of dense areas of collagen (Figs 8.135a-d) ●● myxoid stroma and/or haemorrhage result in areas of fluid T2W SI (Fig. 8.135f) ●● the split fat sign represents a rim of fat around intermuscular lesions ●● pressure erosion of bone/cortical scalloping or thickening is seen in 6-37% of cases, and fibromatosis is one

of the few benign lesions associated with neurovascular encasement (Fig. 8.135g)

●● lipofibromatosis: is a rare benign fibro-fatty soft-tissue tumour which usually occurs in the distal extremities, but may also be located in the head, neck or trunk

●● it presents as a slowly growing painless mass involving subcutaneous or deep tissues and nearly always affects children: ●● 20% of cases are congenital and the condition is twice as common in males ●● it is an infiltrative but non-metastasising lesion, consisting of adipose tissue containing fibroblastic septa

●● MRI findings: ●● lesions have variable MRI features, depending on the proportion of fat and fibroblastic tissue, but it is

typically predominantly hyperintense on T1W sequences (Figs 8.136a, b), with intermediate signal intensity fibrous components, and variable contrast enhancement involving the fibrous component

Intermediate (Rarely Metastasising) Fibroblastic Tumours ●● solitary fibrous tumour:392,398,399 was previously classed as a perivascular tumour but shows no histological

evidence of pericytes and is more closely related to fibrous tumours: ●● it may have both benign and malignant (10-15%) forms and most commonly involves the lower

extremities, pelvis and retroperitoneum ●● MRI findings:

●● a non-specific soft-tissue mass with intermediate/mild increased SI on T1W (Fig. 8.137a) and intermediate/mild increased SI on T2W images (Fig. 8.137b)

●● prominent vascular channels may be seen within and at the periphery of the lesion, and lesions commonly contain a vascular pedicle (Fig. 8.137c), while the presence of tumour necrosis suggests malignancy

●● contrast enhancement may be uniform or non-uniform ●● myofibroblastic inflammatory tumour:400 is a lesion composed of myofibroblastic spindle cells accompanied

by an inflammatory infiltrate: ●● it typically affects the soft tissues and viscera of children and young adults and involvement of

the musculoskeletal system is unusual ●● adherence to vessels and pressure erosion of bone are recognised features

●● MRI findings: ●● low SI on T1W (Fig. 8.137d) and low/intermediate SI on T2W sequences (Fig. 8.137e), with contrast

enhancement ●● myofibroblastic sarcoma: represents a tumour with fibromatosis-like features but possessing a low metastatic potential ●● MRI findings:

●● are very similar to fibromatosis or fibrosarcoma (Figs 8.137f, g)

Malignant Fibroblastic Tumours ●● adult fibrosarcoma: has no specific MRI appearances compared to other high-grade soft-tissue sarcomas ●● myxofibrosarcoma:401 formerly termed myxoid MFH: ●● MRI findings:

●● the lesion may have typical myxoid features, or show indeterminate low/intermediate T1W (Fig. 8.138a) and heterogeneous increased T2W SI (Fig. 8.138b)

●● it has a tendency to extend along fascial planes, forming a distinctive fascial tail ●● low-grade fibromyxoid sarcoma (LGFMS):402 is a rare slow growing soft-tissue tumour that affects young and

middle-aged adults: ●● the majority of lesions arise from either subcutaneous fat (7%), or from the deep soft tissues (93%) of

the limbs or chest wall

●● MRI findings: ●● rarely reported, having non-specific appearances of a well-defined lobular mass with heterogeneous SI,

predominantly low/isointense on T1W (Fig. 8.138c) and iso/hyperintense on T2W with variable enhancement

●● a ‘brain gyriform’ pattern of alternating hypointense and hyperintense signal intensity is fairly common (Fig. 8.138d)

●● less commonly intralesional nodules are present (Fig. 8.138e) and rarely, areas of signal void may occur due to tumour calcification (Fig. 8.138c)

●● benign fibrohistiocytic tumours: include GCT of tendon sheath (GCTTS) and PVNS (see Chapters 3 and 6) and benign fibrous histiocytoma

●● intermediate (rarely metastasising) fibrohistiocytic tumours: include plexiform fibrohistiocytic tumour and GCT of soft tissue

●● malignant fibrohistiocytic tumours (MFH) have been removed from the WHO 2013 classification of softtissue tumours and are to some extent a diagnosis of exclusion, now classified as undifferentiated/unclassified sarcomas353

●● GCT of soft tissue: a rare tumour which is histologically similar to GCT of bone: ●● it occurs in the superficial soft tissues of the upper and lower extremities and may be associated with

Paget’s disease ●● it is a benign tumour with potential for malignant transformation, recurrence and metastasis

●● MRI findings: ●● an intermediate/low SI T1W (Fig. 8.139a) and low SI T2W mass (due to haemosiderin deposition)

(Fig. 8.139b) with associated peripheral mineralisation and enhancement following contrast (Fig. 8.139c)

●● benign smooth muscle tumours: include leiomyoma of deep soft tissue ●● malignant smooth muscle tumours: include leiomyosarcoma

●● leiomyoma of deep soft tissue: is an extremely rare benign tumour with only a few cases reported, including lesions involving the elbow region, groin and popliteal fossa

●● lesions are located in the deep subcutis or skeletal muscle (Figs 8.140a, b), and of 21 cases in the literature, 10 involved the extremities

●● most lesions measure more than 5 cm in diameter, and radiologically their large size and rich vascularisation may mimic a soft-tissue sarcoma

●● age at presentation is wide (3-62 years; mean 25 years), with an equal male to female incidence ●● MRI findings:

●● intermediate SI on T1W and (Fig. 8.140a) intermediate/high SI on T2W images (Fig. 8.140b) with peripheral, homogeneous or heterogeneous enhancement following contrast

●● lesions may include areas of fatty change and fibrosis ●● extensive areas of signal void due to calcification is a characteristic feature (Figs 8.140a, b), described as

‘mulberry-like’

●● leiomyosarcoma: is a relatively rare lesion, accounting for 5-10% of all STS ●● it typically presents in adults, usually post-menopausal women, but occurrence in younger individuals has

been reported in AIDS and after organ transplantation

●● the thigh is the most common site of involvement in the extremities ●● pathologically: leiomyosarcomas are divided into 4 subtypes based on their site of origin:

●● retroperitoneal, cutaneous/subcutaneous (Fig. 8.141a), vascular (Figs 8.141b, c) and deep soft tissue (Fig. 8.141d)

●● bone involvement may be primary, or secondary to metastatic spread from a soft-tissue lesion ●● MRI findings:

●● the appearances are similar to other high-grade soft-tissue sarcomas, with intermediate T1W SI, increased T2W SI and heterogeneity due to haemorrhage and necrosis

●● the presence of areas of hyalinisation (Fig. 8.141d) or metaplastic bone formation may result in foci of low T2W SI, which may suggest the diagnosis

●● also, tumours of vascular origin may show encasement of the vessel of origin, often the inferior vena cava (IVC) or lower extremity veins, which may be relatively central within the tumour (Fig. 8.141b)

●● benign pericytic tumours: include glomus tumours and myopericytoma ●● malignant pericytic tumours: include malignant glomus tumour, which display marked nuclear atypia and/or

mitotic activity and if lesions are >2 cm without nuclear atypia or mitotic activity, they are considered to be of uncertain malignant potential

●● glomus tumours: are benign tumours derived from the neuromyoarterial glomus bodies, a specialised arteriovenous anastomosis responsible for thermoregulation: ●● they are classically located in the subungual region, digits and palms due to the high concentration of

glomus bodies in these regions, and present with pain and joint tenderness (see Chapter 3) ●● they usually present between the ages of 30-50 years, with a roughly equal incidence in men and women

●● glomangiomatosis:408 is a rare condition that refers to multiple glomus tumours, which may not be located in the subungual region, frequently with atypical MRI appearances (Fig. 8.142a)

●● MRI findings: ●● glomus tumour presents as a lesion that is typically markedly hyperintense on T2W and shows variable

T1W SI depending upon its histological cellular pattern (vascular, myxoid or solid) (Figs 8.142b, c)

●● avid contrast enhancement reflects the vascular nature of the lesion (Fig. 8.142d), with strong arterial phase enhancement and a tumour blush on MR angiography

●● lesions can result in erosion of the subungual distal phalanx

●● infantile myofibromatosis: is a process characterised by benign proliferation of fibrous tissue, usually presenting as a slowly growing mass

●● involvement and compression of peripheral nerves, including the brachial plexus is recognised and may result in pain and loss of function

●● 50% of lesions are present at birth and most occur within the first 2 years of life, with a male predominance of 1.7:1 ●● multiple myofibromas: in adulthood are uncommon and more frequently occur in women, presenting as

small flesh coloured or purple cutaneous nodules410 ●● 3 types of myofibromatosis are recognised: solitary (myofibroma), multi-centric without visceral involvement

and multi-centric with visceral involvement (a disorder with 75% mortality in the neonatal period): ●● the former 2 types may be associated with spontaneous regression

●● MRI findings: ●● variable features are described, including well-defined or ill-defined margins ●● lesions are typically hypointense on T1W images (rarely hyperintense) and range from hypo-to

hyperintense on T2W images, with variable contrast enhancement, usually peripheral with a target-like appearance or occasionally homogeneous

●● calcification may be present, while osseous involvement usually affects the metaphyseal regions of long bones and may be bilateral and symmetrical

●● angioleiomyoma: is a benign tumour arising from vascular smooth muscle (tunica media) and presents most commonly between the 3rd and 5th decades of life, frequently involving the lower extremities in middle-aged women

●● clinically: it presents as a solitary painful mass in ~60% of cases, usually measuring <2 cm in size and located in the cutaneous or subcutaneous tissues: ●● lesions may show an increase in size with activity, especially when arising in the hand

●● MRI findings: ●● angioleiomyomas are usually well-defined, small lesions with intermediate SI on T1W images

(Fig. 8.143a) and intermediate/increased SI on T2W images (Fig. 8.143b) ●● lesions generally demonstrate diffuse enhancement, with areas of increased SI on T2W sequences typically

showing stronger enhancement ●● small curvilinear structures may be evident in the lesion due to tortuous muscular vascular channels

(Fig. 8.143c) and a hypointense rim is seen on T2W images due to a fibrous capsule ●● large lesions may be associated with extensive tumour calcification

●● benign skeletal muscle tumours: include rhabdomyoma ●● malignant skeletal muscle tumours: include embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma and

pleomorphic rhabdomyosarcoma

●● rhabdomyoma: is classified as cardiac and extracardiac, the latter is further classified as adult, foetal and genital

●● they are extremely rare and almost all involve the head and neck region ●● they most commonly occur over the age of 40 years with a male predominance, and only a few cases of

rhabdomyoma of the extremity have been reported ●● MRI findings:

●● variable isointensity-to-hyperintensity on T1W and T2W sequences, and may contain areas of haemorrhage and necrosis

●● the lesions are commonly hyperintense on STIR and show homogeneous or heterogeneous contrast enhancement

●● rhabdomyosarcoma: is the commonest STS of childhood, accounting for ~60% of cases and occurring at any soft-tissue site

●● it represents up to 8% of all childhood cancers and >50% of childhood STS, but <1% of adult malignancies, and 3% of adult STS: ●● embryonal rhabdomyosarcoma: is found in younger patients (2-5 years), and may result in tibial

bowing ●● alveolar rhabdomyosarcoma: occurs in adolescents (15-19 years), often involving the hands and feet and is

the commonest type arising in the trunk and extremities ●● pleomorphic rhabdomyosarcoma: is rare and almost exclusively affects adults, typically involving the

extremities, particularly the thigh ●● spindle cell/sclerosing rhabdomyosarcoma: occurs most frequently in paratesticular sites in children,

and more commonly in the head and neck in adults, the latter carrying a poorer prognosis ●● there is an increased incidence of rhabdomyosarcoma in the non-Hispanic white population, in patients with

neurofibromatosis-1 (NF1), Beckwith-Wiedemann, Li-Fraumeni and Costello’s syndromes, and a possible increased risk in offspring of parents using cocaine and marijuana

●● MRI findings: ●● as for other high-grade soft-tissue sarcomas (Figs 8.144a-d) ●● regional and distant lymph node metastases are seen more frequently than in other subtypes of extremity

sarcoma ●● bone metastases may have a similar appearance to osseous ALL lesions416

●● benign vascular tumours: include haemangioma/vascular malformations, epithelioid haemangioma, angiomatosis and lymphangioma

●● intermediate (locally aggressive) vascular tumours: include Kaposiform haemangioendothelioma ●● intermediate (rarely metastasising) vascular tumours: include papillary intralymphatic angioendothelioma,

haemangioendothelioma and Kaposi sarcoma ●● malignant vascular tumours: include epithelioid haemangioendothelioma and angiosarcoma

●● haemangiomas: are proliferative lesions that usually appear after birth due to pathologic angiogenesis, grow rapidly in the first few years of life and subsequently involute over a period of years

●● they are the commonest vascular soft-tissue lesions, comprising 7% of all benign soft-tissue tumours and being classified as infantile, capillary or cellular

●● the majority of soft-tissue haemangiomas are solitary, with ~20% being multiple ●● haemangiomas may be either deep or superficial and are more common in girls ●● rarely, they may infiltrate tendon sheaths, when the term tenosynovial haemangioma is used, such cases most

commonly located in the hand ●● another rare occurrence is that of haemangioma arising within a peripheral nerve, when the term ‘intrinsic

haemangioma’ of the peripheral nerve is used ●● MRI findings:

●● haemangiomas typically have a multi-lobular appearance resembling ‘a bunch of grapes’ ●● they are isointense (Fig. 8.145a) or mildly hyperintense (Fig. 8.145b) to muscle on T1W images,

heterogeneously hyperintense on T2W/STIR images (Figs 8.145c, d) and show intense homogeneous enhancement following contrast

●● the presence of high-flow vessels may result in signal voids on SE images (Fig. 8.145e) ●● intramuscular haemangiomas often contain tubular vessels arranged in a parallel fashion ●● small areas of fat may also be seen within and around the lesion (Fig. 8.145a), and fibro-fatty deposition

occurs with involution of infantile haemangiomas

Vascular Malformations357,363,418 ●● vascular malformations: result from errors of morphogenesis and are classified according to the constituent

vessels as arterial, venous (cavernous), lymphatic, capillary or mixed ●● they are present at birth and grow in proportion to the growth of the child, with no tendency to spontaneous

regression ●● the prevalence is estimated at 1.5% in the general population ●● venous, lymphatic and capillary malformations are slow-flow lesions, while arteriovenous malformations/

fistulae (AVMs/AVFs) are high-flow lesions ●● they are usually superficial in location but may also be deep, in which case they are usually intramuscular

●● venous (cavernous) malformations: are the commonest vascular malformations of the extremities (accounting for 50-66%), usually arising in the flexor muscles of the forearm and quadriceps muscles: ●● they range from large varicosities to cystic spaces, which may contain phleboliths or thrombus ●● the lesions may be limited to a single tissue or may invade all tissues in the limb, including muscles,

tendons, nerves, fat or bone ●● bone involvement includes bone remodelling, hypertrophy and demineralisation, with potential for

inducing pathological fracture ●● lymphatic malformations: are comprised of chyle-filled macro-or microcysts:

●● the majority are present at birth and 90% are identified before the age of 2 years ●● macrocystic lesions: were previously termed lymphangiomas or cystic hygromas and may result from

obstruction of major lymphatic channels during development ●● the commonest site is the posterior triangle of the neck or the axilla, with the limbs less frequently

involved ●● microcystic lesions: are usually cutaneous and infiltrating

●● AVMs/AVFs: comprise ~10% of extremity vascular malformations: ●● AVFs are formed by the direct communication between arteries and veins, whereas AVMs consist of

feeding arteries and draining veins connected by multiple dysplastic vessels ●● AVMs typically present in puberty as a result of infection, thrombosis or trauma ●● massive skeletal overgrowth and limb hypertrophy are relatively common

●● a variety of syndromes are associated with vascular malformations: ●● Maffucci’s syndrome: comprises multiple enchondromas and soft-tissue cavernous haemangiomas

●● Osler-Weber-Rendu syndrome (hereditary haemorrhagic telangiectasia): is a systemic fibrovascular dysplasia of all vessels and comprises telangiectasia, AVMs and aneurysms, possibly with associated osseous lesions

●● Klippel-Trenaunay-Weber syndrome: consists of cutaneous haemangioma, bone and soft-tissue hypertrophy and varicose veins, being usually unilateral and affecting the lower limbs, occasionally with associated AVF

●● Proteus syndrome: a rare vascular anomaly associated with verrucous naevi, lipoma/lipomatosis, macrocephaly, asymmetric limbs with partial gigantism of the hands and feet, and cerebriform plantar thickening, with MRI demonstrating abundant fat within the malformation

●● Kasabach-Merritt syndrome: a rare complication of large haemangiomas, in which there is thrombocytopenia and purpura

●● MRI findings: ●● MRI is capable of defining the extent of vascular malformations (classified as focal, multi-focal or diffuse)

and DCE-MRI can distinguish slow-flow from high-flow lesions: ● this distinction helps guide treatment towards percutaneous embolisation for slow-flow lesions and

transarterial embolisation for high-flow lesions ●● venous (cavernous) malformations: typically well-defined, lobular lesions that are isointense on T1W

images (Fig. 8.146a), hyperintense on T2W/STIR images (Figs 8.146b, c), commonly with low SI internal septa (Figs 8.146b, c) and enhance diffusely following contrast:

● phleboliths and thrombi appear as low SI central dots (Fig. 8.146d) and fluid-fluid levels may be seen on T2W images (Fig. 8.146e)

● flow voids are usually absent, and signal voids are usually caused by phleboliths, fibrous striations and thrombosed vessels

● lesions adjacent to bone may stimulate a chronic periosteal response (Fig. 8.146f) ● DCE-MRI shows gradual delayed contrast filling, without arterial enlargement or AV shunting

●● lymphatic malformations: consist of chyle-filled cysts lined with endothelium: ● macrocystic lesions are hypointense on T1W (Fig. 8.147a) and hyperintense on T2W images

(Fig. 8.147b), showing septal enhancement following contrast, and fluid-fluid levels may be seen ● microcystic lesions have smaller (<2 cm) cysts within a more solid matrix, are of intermediate SI

on T1W and T2W sequences, tend to show diffuse enhancement and cannot be distinguished from venous malformations

● AVMs/AVFs: appear as prominent serpentine vessels with areas of signal void due to rapid blood flow within the dysplastic vessels, non-mass-like soft-tissue infiltration without respect for tissue planes, and haemorrhagic and thrombotic foci

● adjacent dilated, tortuous feeding arteries and draining veins may be seen, the latter being demonstrated to advantage by enhanced MR angiography and DCE-MRI, which shows early enhancement and venous shunting

●● in the differentiation of haemangiomas/vascular malformations from malignant soft-tissue masses: the finding of the combination of lobulation, septation and central low SI dots is exclusive to haemangiomas and not seen in sarcomas

●● kaposiform haemangioendothelioma (KHE): is a vascular endothelial neoplasm of borderline malignancy, which is frequently present at birth: ●● it is usually solitary and located in the extremities, retroperitoneum or trunk, being associated with

thrombocytopenic anaemia and consumptive coagulopathy as part of Kasabach-Merritt syndrome ●● it has similar imaging features to infantile haemangioma, but with less well-defined margins and smaller

feeding and draining vessels ●● epithelioid haemangioendothelioma: arises from medium/large blood vessels, involving the extremities,

bone, lung, liver and head and neck: ●● clinically: patients in the 4th and 5th decades are most commonly affected ●● cutaneous lesions present as raised nodules or plaques

●● angiosarcoma: is an aggressive vascular malignancy involving the skin, subcutaneous and deep soft tissues, with less frequent involvement of bones,420 solid organs, head and neck: ●● predisposing factors include previous radiotherapy and lymphoedema ●● the tumour contains anaplastic haemangiomatous and lymphangiomatous components ●● local recurrence and distant metastases are common

●● MRI findings: ●● haemangioendothelioma and angiosarcoma display similar imaging features of an aggressive infiltrative

soft-tissue mass with non-specific signal characteristics (Fig. 8.148) ●● intermediate SI on T1W images and hyperintensity on T2W/STIR images, with or without evidence of

intralesional haemorrhage

●● benign chondro-osseous tumours: include soft-tissue chondroma ●● malignant chondro-osseous tumours: include mesenchymal chondrosarcoma and extraskeletal osteosarcoma

●● soft-tissue chondroma: is a rare benign lesion composed of hyaline cartilage, and accounting for ~1.5% of benign soft-tissue tumours

●● clinically: it most commonly presents in the 30-60 year age range, being slightly more common in men and typically located in the hands or feet, usually near a joint, although they can occur in a variety of locations423-426

●● pathologically: it is thought to arise either from soft-tissue fibrous stroma or from synovial tissue in tendon sheaths and joints

●● MRI findings: ●● soft-tissue chondromas typically range from 0.5 to 3 cm in dimension, and the SI characteristics are as

for intramedullary chondromas, being intermediate SI on T1W (Fig. 8.149a) and hyperintense on T2W images (Fig. 8.149b)

●● chondral-type calcification appears as foci of punctate or curvilinear signal voids (Fig. 8.149b), which if extensive result in predominantly low T2W SI

●● adjacent osseous pressure erosion may develop (Fig. 8.149b)

●● extraskeletal mesenchymal CS: accounts for ~30-75% of mesenchymal CS, typically affecting adults between 15 and 35 years of age, more common in women, with the thigh being the commonest musculoskeletal site

●● myxoid chondrosarcoma: is a second subtype of extraskeletal CS, which is more common and less aggressive than mesenchymal CS

●● MRI findings: ●● typically intermediate SI on T1W (Fig. 8.150a) and T2W images with heterogeneous, prominent

enhancement following contrast (Fig. 8.150b) ●● the SI on T2W sequences tends to be slightly less hyperintense than that seen in conventional CS and areas

of necrosis may be evident ●● serpentine signal voids may also be seen due to tumour vessels ●● intralesional calcification may be dense, ring and arc, irregularly striped or scattered in morphology and

distribution, resulting in signal voids (Figs 8.150a, b), the latter with a ‘black pepper’ appearance

●● extraskeletal osteosarcoma (ESOS): is a rare lesion accounting for <4% of all osteosarcomas and ~1.2% of all soft-tissue sarcomas, the majority of cases being high-grade spindle cell tumours

●● previous radiation is a risk factor for developing ESOS ●● almost 50% involve the deep compartment of the thigh, with other common sites including the upper limb,

retroperitoneum and trunk ●● clinically: ESOS usually presents with a soft-tissue mass which may be painful or painless, and presentation is

typically after the age of 40 years, forming a distinctly older patient group than seen in OS of bone ●● as with skeletal OS, several histological subtypes of ESOS are recognised, including osteoblastic,

chondroblastic, fibroblastic, telangiectatic and small cell

●● MRI findings: ●● a relatively well-defined heterogeneous mass, which is usually 8-10 cm in size at presentation ●● the SI characteristics are non-specific in comparison to other high-grade soft-tissue sarcomas

(Fig. 8.151a), and intralesional haemorrhage is not uncommon, with extreme cases mimicking a haematoma

●● however, tumour calcification is common (68% of cases on radiography) and may be an indicator of the diagnosis (Fig. 8.151b)

●● in such cases, differential diagnosis includes myositis ossificans and synovial sarcoma ●● rarely, the lesion arises superficial to the fascia (Fig. 8.151c)

●● benign tumours of uncertain differentiation: include intramuscular/juxta-articular myxoma and angiomyxoma, pleomorphic hyalinising angiectatic tumour, ectopic hamartomatous thymoma and acral (digital) fibromyxoma

●● intermediate (locally aggressive/rarely metastasising) tumours of uncertain differentiation: include haemosiderotic fibrolipomatous tumour, angiomatoid fibrous histiocytoma, ossifying fibromyxoid tumour and mixed tumour/myoepithelioma/parachordoma, phosphaturic mesenchymal tumour (benign or malignant) and atypical fibroxanthoma

●● malignant tumours of uncertain differentiation: include synovial sarcoma (NOS, spindle cell, biphasic), epithelioid sarcoma, alveolar soft part sarcoma, clear cell sarcoma of soft tissue, extraskeletal myxoid chondrosarcoma, desmoplastic small round cell tumour, Ewing sarcoma of soft tissue and neoplasms with perivascular epithelioid cell differentiation (PEComa) and intimal sarcoma

●● malignant mesenchymoma is no longer included in the current classification and PNET has been dropped as a synonym for Ewing’s, in order to avoid confusion with CNS tumours

●● myxoma: may occur in an intramuscular (Figs 8.152a-c), intermuscular (Figs 8.152d, e), subcutaneous or juxta-articular location

●● intramuscular myxoma: differs from juxta-articular myxoma in that it is more common in women ( juxtaarticular myxoma is more common in men), and tends to occur in the large muscles around the shoulder and in the thigh ( juxta-articular myxomas are more common around the knee)433

●● pathologically: it is a true neoplasm composed of bland spindle-shaped stellate cells within an abundant myxoid stroma and pseudocapsule

●● the single most common location is the thigh (~50%), and it also commonly involves the shoulder girdle, buttocks and upper extremity, with less frequent involvement of the distal extremities and paraspinal434 musculature

●● an association with fibrous dysplasia is recognised, the combination being termed Mazabraud’s syndrome

●● clinically: myxomas typically present as slowly growing painless masses, with a wide age of presentation (mean age 52 years)

●● absence of expression of the immunohistochemical marker MUC4 is a helpful feature in confirming an intramuscular myxoma in cases when imaging and histology alone are unable to differentiate between a myxoma and low-grade fibromyxoid sarcoma (LGFMS)435

●● MRI findings: ●● myxomas are well-defined, often lobular masses measuring ~5 cm in mean dimension, although

occasionally reaching a diameter of 14 cm ●● on T1W images, they are most commonly homogeneous (60%) and hypointense (~80%) (Figs 8.152a, d)

to muscle or occasionally isointense (Fig. 8.152f) ●● on T2W/STIR images, myxomas demonstrate fluid SI (Figs 8.152b, e), which may be homogeneous or

heterogeneous in the presence of hypointense fibrous septa ●● a hypointense fibrous pseudocapsule may also be evident on T2W images (Fig. 8.152e) ●● a thin rim of fat may be seen around the lesion on T1W images, probably due to localised muscle atrophy

and most prominent at the poles, being referred to as the ‘bright caps sign’ (Fig. 8.152f), while perilesional oedema is demonstrated in ~80% of cases (Fig. 8.152g)

●● following contrast, mild/moderate enhancement is seen, which may be septal/peripheral (Fig. 8.152h), or central/nodular (Fig. 8.152c)

●● angiomyxoma: also termed deep ‘aggressive’ angiomyxoma, is a rare lesion typically located in the pelvis/ perineum and affecting women in >90% of cases, typically in the 2nd-4th decades

●● MRI findings: ●● the tumour is isointense on T1W images (Fig. 8.153a) and shows moderate enhancement following

contrast ●● T2W images are characteristic, showing a hyperintense mass with a swirled or laminated appearance due

to the fibrovascular stroma (Fig. 8.153b) ●● prominent peripheral vessels, a ‘finger-like’ growth pattern and cystic degeneration may be seen, while

mildly restricted diffusion has been reported on DWI

●● ossifying fibromyxoid tumour: is a well circumscribed, lobular hard tumour covered by a thick fibrous capsule, usually arising in the deep subcutaneous tissues of the limbs, although it may also occur in the deep compartment

●● it is slightly more common in men and the median age of presentation is ~50 years ●● thought to be of neuroectodermal origin, it consists of spindle cells in a fibromyxoid stroma, with associated

bone formation

●● previously considered to be a benign lesion, it is now classified as an intermediate-grade sarcoma with typical, atypical and malignant subtypes, and is associated with a recurring rearrangement of PHF1 on chromosome 6p21

●● MRI findings: ●● a mass that is of intermediate/low SI on T1W (Fig. 8.154a) and heterogeneous high SI on T2W images

(Fig. 8.154b), with foci of signal void due to calcification ●● the calcified components are typically hypointense on T1W and T2W sequences, but fatty marrow may

be visualised within ossified components on T1W imaging ●● the fibrous capsule appears hypointense on T2W sequences (Fig. 8.154b)

●● synovial sarcoma (SS): is one of the commonest primary STSs (~10% of cases), most cases arising in the 20-40 year age group

●● it is also the 2nd commonest STS of childhood, with ~30% of cases presenting before the age of 20 years, and also the commonest STS of the foot and ankle in the 6-45 year age group

●● clinically: SS usually presents as a painless mass, although a history of localised pain may have been present for many years

●● pathologically: the lesion is not related to the synovium, but arises from mesenchymal tissue that undergoes differentiation to give a synovial histological appearance

●● SS typically occurs in an intermuscular location near a joint, most commonly in the lower extremity, with only 5% actually being intra-articular or intrabursal: ●● 2 histological subtypes are recognised, biphasic (containing epithelial and spindle-cell elements),

and monophasic (containing only spindle cell elements) ●● MRI findings:

●● ~70% of SS are located within 5 cm of a synovial joint (Figs 8.155a-c), and may result in erosive or infiltrative osseous involvement

●● the lesion is typically oval and nodular with heterogeneous intermediate SI on T1W images (Fig. 8.155a) and increased SI on PDW/T2W images (Figs 8.155b, c), showing heterogeneous contrast enhancement, with greater heterogeneity seen in larger lesions

●● a cystic component is seen in 77% and intratumoural haemorrhage in 73% (Figs 8.155d, e), with calcification demonstrated in 11-30% of cases and appearing as areas of signal void

●● cystic SS:441 is also reported and demonstrates multi-locularity with well circumscribed walls and internal septa, the majority containing fluid-fluid levels (Fig. 8.155f)

●● the combination of calcification, fibrosis, haemosiderin deposition, solid tumour mass and necrosis and haemorrhagic areas result in a ‘triple signal’ intensity in approximately 50% of lesions

●● non-aggressive appearances of SS:442 have been described in ~1/3 of cases, including homogeneous intermediate or slightly hyperintense T1W SI, T2W hyperintensity and a mean size of 4.8 cm (Fig. 8.155g)

●● certain imaging features also have prognostic implications:442 features suggestive of high-grade tumour include proximal distribution, tumour size >10 cm, absence of calcification, presence of cystic areas and haemorrhage, and presence of the ‘triple signal’ pattern

●● epithelioid sarcoma: is a rare soft-tissue tumour, which typically affects adolescents and young adults between 10 and 35 years of age

●● ~60% of cases involve the distal upper limb, particularly the hands and forearms, with the distal and proximal lower limbs being affected in 15% and 12% of cases, respectively

●● pathologically: the lesion may be subcutaneous, presenting as a solitary or multi-lobular, irregular mass: ●● deep-seated lesions are typically larger and firmly attached to tendons, tendon sheaths and fascia, with

a tendency to spread along neurovascular bundles, resulting in vascular invasion and metastasis ●● lesions arising in the proximal extremities have a poorer prognosis

●● MRI findings: ●● the tumour ranges from 2.5 to 19 cm in dimension, the vast majority being poorly-defined with

infiltrative margins, arising either in an intramuscular location (Figs 8.156a-c) or in the subcutaneous tissues, in which case they have a ‘flattened’ appearance

●● the tumour is usually homogeneous and isointense to muscle on T1W images (Fig. 8.156a), but may show areas of increased or decreased SI due to haemorrhage or necrosis

●● the T2W SI is very variable, from hypointense to fat (Fig. 8.156b), to hyperintense to fat and with variable enhancement (Fig. 8.156c)

●● additional features: peritumoural muscle oedema may be seen in 50% of cases, reactive cortical thickening without medullary invasion, regional lymphadenopathy in 50% of cases and rarely, calcification

●● ASPS: is a rare tumour, accounting for 0.5-1% of all STS and usually affecting young adults ●● clinically: the lesion is slow growing and therefore commonly asymptomatic, apart from the presence of

a mass, with median size of 6 cm (ranging from 2.3 to 20 cm) ●● alternatively, since the tumour is highly vascular, it may present as a pulsatile mass with an audible bruit,

mimicking an AVM ●● most lesions are located in the thigh or lower leg (55% in the lower limbs), with 18% in the upper limbs,

while the head and neck area may be involved in children ●● metastases are relatively common at presentation ●● MRI findings:

●● ASPS is typically heterogeneously hyperintense on both T1W (Fig. 8.157a) and T2W/STIR (Fig. 8.157b) images, with all cases showing either homogeneous (40%) or heterogeneous (60%) enhancement following contrast (Fig. 8.157c), and peripheral enhancement seen in necrotic lesions

●● central or peripheral round/serpentine flow voids are seen in ~70% of cases, indicative of its vascular nature (Figs 8.157a-c)

●● ASPS should be considered in the presence of flow voids in a T1W hyperintense lesion

●● CCSST: is a rare tumour, which is also termed malignant melanoma of soft parts due to its melanocytic differentiation, and most commonly affects young to middle-aged adults

●● poor prognostic features include male gender, age <30 years, location in the trunk and size greater than 5 cm

●● pathologically: CCSST arises in the deep soft tissues of the limbs, adjacent to tendons, aponeurosis and fascial structures: ●● the tumour is well-defined, lacking perilesional oedema, bone erosion, necrosis and satellite nodules,

therefore appearing as a ‘benign’ lesion ●● the majority arise in the lower limbs (most commonly the foot and thigh) and less commonly, the

upper limb ●● regional lymph node metastases occur in 12-43% of patients, compared with 2-6% of patients diagnosed with

other STSs ●● MRI findings:

●● CCSST is usually a well-defined oval/fusiform or round lesion, which is occasionally lobulated and least commonly ‘spider-like’ in shape, ranging in size from 1.7 to 10 cm

●● the majority of lesions are homogeneous and hyperintense to muscle (~50%) on T1W/PDW images (Fig.8.158a) due to the paramagnetic effect of contained melanin

●● the remainder are either isointense or hypointense to muscle on T1W images ●● the majority are also hyperintense on T2W images and less commonly of intermediate SI or hypointense

(Fig. 8.158b) ●● marked enhancement following contrast is typical

Extraskeletal Myxoid Chondrosarcoma453,454 ●● extraskeletal CS: accounts for ~2% of all STS, with extraskeletal myxoid CS being the commonest subtype ●● the mean age at presentation is 54-58 years, with a reported age range of 4-92 years

●● 61% of tumours arise in the lower extremities, with the thigh being the commonest location, and the majority (78%) lie deep to the fascia

●● due to its myxoid nature, the tumour is typically iso/hypointense to muscle on T1W images (Fig.8.159a) and markedly hyperintense on T2W/STIR (Figs 8.159b, c)

●● a lobular growth pattern is typical and following contrast, the characteristic septal/peripheral enhancement pattern of chondral tumours is seen (Fig. 8.159d)

Soft-Tissue Lymphoma456-458 ●● lymphoma: involving skeletal muscle is rare, reported in 1.4% of all cases of lymphoma and can occur due

to haematogenous spread from systemic involvement, from extraosseous spread of bone lymphoma, or most uncommonly as a primary muscle lesion

●● ~0.3% of Hodgkin’s lymphoma and 1.1% of NHL arises as primary muscle disease ●● muscle lymphoma: may also represent a musculoskeletal complication of AIDS, in which case it must be

differentiated from pyomyositis and polymyositis ●● since the extension of bone lymphoma to adjacent soft tissues is a common occurrence, the diagnosis of

primary muscle lymphoma requires certain criteria, including: ●● a large soft-tissue mass with no or minimal bone marrow involvement ●● the absence of systemic or nodal disease at initial presentation

●● the commonest sites involved are the thigh, calf, the upper arm and shoulder, but primary muscle lymphoma can occur in all body regions

●● clinically patients present with local muscle pain and swelling, with muscle wasting, compartment syndrome and rhabdomyolysis rarely reported

●● typically, the lesion involves a long length of the extremity, a growth pattern that is unusual for soft-tissue sarcoma (Fig. 8.160a)

●● the tumour mass is usually diffuse, not limited by anatomical compartments (Fig. 8.160b) with poorlydefined, infiltrative margins, with involvement of more than one muscle compartment being seen in ~50%

●● extension through the deep fascia with resulting involvement of subcutaneous fat (Fig. 8.160c), often in a reticular pattern, and skin (Fig. 8.160d) is also recognised, and extension of tumour along a neurovascular bundle is seen in 27%

●● the tumour is isointense or minimally hyperintense to muscle on T1W images (Fig. 8.160b) and hyperintense to muscle on STIR images (Fig 8.160a)

●● as with other round cell tumours, lymphoma may demonstrate homogeneous intermediate/low SI on T2W images (Figs 8.160d, e) due to the densely cellular nature of the lesion, with perilesional oedema seen in almost half of cases

●● diffuse or irregular enhancement following contrast is typical, with enhancement of deep and superficial fascia seen in 84%, but non-enhancing lesions have also been described

●● adjacent bone marrow SI abnormalities are not uncommon (Fig. 8.160f) and peritumoural oedema is also a feature that helps distinguish lymphoma from other primary STSs (Fig. 8.160f)

●● ganglia: are relatively common soft-tissue masses that can occur at any age, but are more common in teenagers and young adults, with a male to female ratio of 1:3

●● they are composed of thick-walled cystic spaces containing myxoid tissue and are thought to represent a degenerative phenomenon, most commonly associated with joints, tendons and ligaments

●● primary intramuscular ganglia with no joint communication are rare, being most commonly identified in the quadriceps muscles (Fig. 8.161a)460

●● MRI findings: ●● the lesion is typically elongated, well-defined and has a lobular outline (Figs 8.161a-c) ●● as with other ganglia, they are relative hypointense on T1W (Fig. 8.161b) and show marked

hyperintensity on T2W/STIR images (Figs 8.161a, c) ●● a thin hypointense wall and hypointense internal septa are characteristic (Fig. 8.161c), both showing

enhancement following contrast

●● granuloma annulare: is an uncommon benign skin condition that may be classified as localised, generalised, perforating or subcutaneous

●● the latter is termed subcutaneous granuloma annulare (SGA) and may present as a soft-tissue tumour most commonly affecting children (typical age range 2-5 years), manifesting as a non-mobile, painless mass

●● there is a recognised association with insulin dependent diabetes mellitus (IDDM) in ~5%, and lesions may show regression with improved blood sugar control

●● ~65% occur in a pretibial location and less commonly in a prepatellar location, the upper limb or the buttock

●● MRI findings: ●● the lesion has ill-defined margins and is surrounded by oedema-like SI, which can extend into the

surrounding subcutaneous tissues for several centimetres, with extension to but not through the adjacent deep fascia being typical

●● on T1W images, the lesion is isointense or slightly hyperintense to adjacent skeletal muscle (Fig. 8.162a) and on T2W/STIR images, heterogeneous increased SI is seen

●● following contrast, enhancement may be either homogeneous or heterogeneous, with enhancement of the oedema-like SI also typically seen (Fig. 8.162b)

●● DFSP: is an uncommon soft-tissue fibrosarcoma representing 2-6% of STS, which typically arises in the dermis as a multi-nodular mass that spreads along fascial planes into the subcutaneous tissue and muscle, and metastasises in 2-5% of cases

●● it occurs most commonly between the 2nd-5th decades and is slightly more common in males ●● DFSP most commonly occurs in the trunk (~50% of cases) and limbs, followed by the head and neck,468 and

lesions may range from 1 to 25 cm in dimension ●● clinically: it is a slow growing skin tumour, which develops into a nodular mass, with eventual fungation if

left untreated ●● it is closely related to the overlying skin, but typically does not involve the deeper structures ●● several subtypes exist, of varying histological grade469 ●● MRI findings:

●● DFSP usually appears as a well-defined (rarely irregular), multi-lobular superficial mass, which may extend deep to the skin (Figs 8.163a, b), with a mean depth of 17 mm (range 8-60 mm)

●● occasionally, the lesion may be purely deep with no superficial component identified, and infiltration of the underlying bone is rarely reported470

●● the tumour is usually isointense to muscle on T1W images and less commonly is hypo-or hyperintense (Fig. 8.163a)

●● on T2W the lesion is either hyperintense or of intermediate SI (Fig. 8.163b), and is always hyperintense on FS T2W FSE/STIR images, showing either uniform or heterogeneous contrast enhancement

●● hypointense non-enhancing linear bands within the lesion are characteristic, and are thought to represent fibrotic areas of increased collagen

●● epidermoid cyst: is a common benign soft-tissue tumour that arises in the skin, thought to occur due to the deep migration of epidermal tissue

●● in the majority of cases, the diagnosis is clinically evident but occasionally the cyst may increase to such a size that it mimics a STS

●● MRI findings: ●● the signal characteristics will depend upon the chemical composition and physical state (fluid vs. solid) of

the cyst contents, and can be highly variable ●● epidermoid cysts are located in the subcutaneous tissues and involve the overlying skin, being surrounded

by a thick, well-circumscribed capsule and ranging in size from 2 to 10 cm (mean 5.2 cm), intramuscular extensions being rare472

●● the lesion is either slightly hyperintense or isointense to skeletal muscle on T1W images (Fig. 8.164a) and hyperintense on T2W and STIR images (Fig. 8.164b)

●● heterogeneity is seen on T2W due to the presence of debris (Fig. 8.164b) ●● either no enhancement or rim enhancement is seen following contrast, but irregular/nodular

enhancement of part of the tumour margin may indicate malignant change

●● fat necrosis: occasionally presents as a soft-tissue mass, usually overlying bony protuberances ●● it may present as a subcutaneous lesion or complicate fatty tumours such as lipoma ●● encapsulated subcutaneous fat necrosis may simulate liposarcoma and spindle cell lipoma, requiring a biopsy

for definitive diagnosis, but a spindle cell lipoma is suggested when located in the posterior neck475 ●● clinically: patients may be asymptomatic or present with pain, skin induration, bruising, skin retraction,

or skin thickening ●● the formation of encapsulated loose bodies in the soft tissue may follow post-traumatic fat necrosis476 ●● aetiological factors: in the development of fat necrosis include trauma, subcutaneous injections,477 collagen

vascular diseases, myeloproliferative disorders and pancreatic disorders, which may result in disseminated lesions

●● MRI findings: ●● subcutaneous fat necrosis appears as a globular lesion with central fat SI, surrounded by irregular

hypointensity on T1W images (Fig. 8.165a), increased SI on FS T2W FSE/STIR images (Fig. 8.165b), and enhancement of the low SI margin may be seen

●● lymphoedema:478-480 may be primary (congenital) or secondary (due to filariasis infection, interruption of lymphatic drainage or after surgical lymphatic resection, usually following axillary or pelvic lymphadenectomy for breast or gynaecological cancers): ●● the lymphatic system comprises deep (subfascial) and superficial drainage systems and lymphatic vessels

transport 10% of interstitial fluid to the bloodstream, with the remainder carried in venous capillaries ●● accumulation of proteinaceous interstitial fluid causes soft-tissue swelling, inflammatory change,

hypertrophy of the subcutaneous fat and soft-tissue fibrosis ●● 2 stages of lymphoedema are described:

●● early: accumulation of interstitial lymphatic fluid without fibrosis, with or without soft-tissue pitting and improvement with limb elevation

●● late stage: fibrotic interstitial tissue response with increased volume of the affected limb, but skin changes and pitting may be absent

●● MRI findings: ●● the accumulation of interstitial fluid equally involves the muscle and subcutaneous fat ●● increased fluid SI is most marked in close proximity to lymphatic vessels (in the subcutaneous fat adjacent

to the deep fascia, and around the deep intramuscular veins) ●● STIR and post-contrast FS T1W sequences reveal a hyperintense honeycomb/reticular pattern

in the subcutaneous fat, increased SI of the deep fascia and around the deep intramuscular vessels (Figs 8.165c-e)

●● MR lymphography: is an emerging technique, in which dilute gadolinium is injected into each web space followed by imaging of the proximal lymphatic vessels and lymph nodes:

● lymphoedema results in delayed peak lymphatic filling, delayed lymph node enhancement, slow washout and a lower peak SI

●● ~50% of patients treated for STS may have a local recurrence (LR), the majority occurring within the first 2 years of treatment

●● features that increase the risk of LR include: ●● poorly-defined lesions, such as fibromatosis due to inadequate surgical tumour margins ●● histologically high-grade tumours ●● tumours located deep to the fascia, due to difficulty in achieving wide margins

●● the post-operative MRI assessment of possible LR requires a knowledge of the preoperative tumour SI characteristics, since tumour recurrence typically has the same SI features

●● from a technical viewpoint the proximal and distal ends of the patient’s scar should be marked with skin capsules: ●● the diagnosis of LR or seroma can usually be made without the need for contrast administration ●● contrast may be of value: in the differentiation of recurrent tumour from haematoma, for the assessment

of recurrent fibromatosis and for the differentiation of the rare post-radiotherapy inflammatory pseudotumour from local recurrence

●● the pattern of enhancement seen with granulation tissue and hyaline fibrosis may be difficult to differentiate from recurrent tumour on standard post-contrast imaging, and DCE sequences may be required

●● the addition of DCE MRI to a standard protocol increases the detection of recurrence from 27% to 97% ●● DWI and ADC mapping is also helpful in identifying recurrence, and is able to differentiate between

recurrence and scar tissue484 ●● MRI findings:

●● LR is characterised by the presence of a distinct nodular soft-tissue mass, typically with intermediate T1W SI (Fig. 8.166a), heterogeneous increased T2W SI (Fig. 8.166b) and enhancement following contrast

●● on DCE MRI, viable tumour produces a rapid early pattern of enhancement in contrast to the slow enhancement of post-treatment hyaline fibrosis and granulation tissue

●● DCE MRI maximum intensity projection imaging obtains residual tumour volume in as little as 5 minutes of scanning time, and post-treatment chemotherapy response can be determined as early as 2 weeks after the first treatment485

●● recurrence of myxoid sarcomas my mimic a post-operative cyst, since these appear hypointense on T1W images and hyperintense on T2W images, similar to the original lesions

●● post-operative appearances: following sarcoma surgery will be affected by (neo)adjuvant treatments including: ●● chemotherapy: neo-adjuvant chemotherapy may be administered for some soft-tissue sarcomas such as

synovial sarcoma and extraskeletal Ewing sarcoma ●● radiotherapy: radiotherapy may be given before or after tumour resection:488

● preoperative radiotherapy carries the benefits of a well-vascularised, well-defined therapy field, resulting in a reduced radiation field volume and dose, with less secondary oedema and fibrotic change

● early wound healing problems may arise within a preoperative radiation field following tumour resection ● myxoid liposarcoma typically shows a particularly favourable response compared to other sarcomas

(Figs 8.167a, b) ● a partial radiological response may represent a significant histological response

●● the use of myocutaneous flaps: myocutaneous flaps are composed of muscle and overlying skin and may be required following extensive tissue resection following sarcoma surgery:

● they may be necessary in up to 2/3 of extremity sarcoma resections and are of various types ● rotational flaps: are rotated into position to cover the soft-tissue defect while preserving the native

neurovascular supply via a pedicle ● free flaps: are detached completely and placed over the soft-tissue defect with the vascular pedicle

re-anastomosed using microsurgical techniques ●● MRI findings:

●● chemotherapy: significant increase in tumour size may occur secondary to chemotherapy-induced intratumoural haemorrhage:

● chemotherapy response can also be indicated by a marked reduction in tumour volume, and signal changes representing necrosis, fibrosis and reactive tissue may be seen

● contrast enhanced subtraction imaging techniques are helpful in distinguishing between residual viable tumour and post-treatment necrosis or spontaneous/chemotherapy-induced haemorrhage482

●● radiotherapy: results in oedema-like SI within the soft tissues, which are maximal at 12-18 months post-treatment and typically resolve by 2-3 years in 50% of cases:

● oedema in the subcutaneous tissues appears as a trabecular or lattice-like pattern of reduced T1W SI and increased FS T2W/STIR SI with associated skin thickening (Fig. 8.167c)

● oedema in muscle results in a more diffuse pattern of increased T2W/STIR SI (Figs 8.167c, d) with minimal enhancement and maintenance of muscle shape and texture, although the muscle may eventually atrophy

● SI changes are more marked and persistent in the intermuscular septa than in the adjacent soft tissues ● post-operative soft-tissue oedema following resection alone resolves sooner than post-operative and

post-radiotherapy oedema ● rarely, an inflammatory pseudotumour may develop following radiotherapy (reported incidence ~1%)

and can be differentiated from recurrent tumour by its dynamic enhancement characteristics: – pseudotumour enhances at 4-7 minutes post-contrast injection, whereas recurrent tumour

enhances 1-3 minutes following contrast ●● myocutaneous flaps:489 demonstrate time-dependent changes in their MR appearances (size, SI

characteristics and enhancement patterns): ● all flaps atrophy with time, demonstrating decreased muscle mass and increased fat content ● initially, all flaps appear relatively oedematous (Figs 8.167e, f ), returning to normal muscle SI in

1/3 of cases between 5 and 21 months from surgery, with more persistent oedema if post-operative radiotherapy has also been given

● initial increased enhancement is seen in ~75% of cases, returning to normal muscle enhancement at 18 months in ~1/3 of cases

● radiotherapy will increase T2W SI and contrast enhancement of flaps ● muscle atrophy: may develop secondary to disuse, post-radiotherapy muscle inflammation, nerve

entrapment or transection, and is seen as diffuse T2W areas of hyperintense muscle oedema in the regions supplied by the transected nerve

● acute denervation changes progress to chronic atrophy by 6-12 months

●● post-operative seroma: also known as a hygroma, represents a well-defined fluid collection at the site of tumour resection, most commonly associated with sarcoma surgery (~90%) and usually seen in the buttock and lower limb (90%)

●● post-operative seroma is reported in 7.7% of patients at 3 months following STS resection, rising to 76% of patients who also had radiotherapy487

●● MRI findings: ●● seromas are well-defined lesions with a thin hypointense pseudocapsule on T2W images ●● 74% show homogeneous low SI on T1W images (Fig. 8.168a) with rim enhancement following contrast,

while 26% show hyperintensity

●● on PDW/T2W images, 79% are homogeneous and hyperintense (Fig. 8.168b) ●● T2W heterogeneity due to septa (Fig. 8.168c), fluid-fluid levels (Fig. 8.168d) or debris may be seen in

21% of cases, with the result that they are slightly more heterogeneous than ganglia or cysts ●● a feathery pattern may be seen arising from the inner margin of the seroma or from the septa ●● the majority are round or oval in cross-section, and are less commonly angular, extending between muscle

planes (Fig. 8.168e), or linear/flame-shaped ●● with time, 66% of seromas decrease in size, whereas ~20% may show an increase in size, complete

resolution taking months to years

●● idiopathic inflammatory myopathies (IIM): include polymyositis, dermatomyositis and inclusion body myositis (IBM)

●● polymyositis/dermatomyositis: are diseases of unknown aetiology that predominantly affect females at any age

●● polymyositis usually presents in the 4th decade of life whereas dermatomyositis has a bimodal age presentation, with peaks in childhood and the 5th decade

●● although not classed as a paraneoplastic condition, dermatomyositis is associated with an increased risk of cancer; particularly malignancies of the lung, colon and ovary

●● the diagnosis is based on the presence of 3 of the following 4 features: ●● proximal and symmetrical muscle weakness, with or without myalgia ●● increased serum creatinine kinase (CK) levels

●● multi-focal myopathic pattern on electromyography (EMG) ●● fibre necrosis/regeneration and mononuclear cell infiltrates without perifascicular atrophy on muscle

biopsy ●● dermatomyositis: is characterised by the addition of a permanent or transient exanthema of the face, chest or

extensor surfaces of the extremities ●● clinically: the diseases are typically chronic and progressive with variable patterns of muscle involvement

between patients ●● similar clinical and MRI features may be seen in IBM, although with distal as well as proximal muscle

weakness of the extremities, more common anterior muscle group involvement (with sparing of rectus femoris), and a greater prevalence in men

●● IBM: is now thought to represent inflammation secondary to myodegenerative disease or following paramyxovirus infection, rather than a primary autoimmune disease

●● MRI is useful for targeting an optimal biopsy site,494 and for evaluating treatment response ●● MRI findings:

●● the primary abnormality is muscle oedema, with the muscles appearing hyperintense on T2W/STIR images (Fig. 8.169a) but essentially normal on T1W images

●● oedema may be either focal or diffuse, but is typically symmetrical and most marked in the proximal muscles

●● the commonest involved muscles include the vasti, glutei, adductors, hamstrings, tibialis anterior, gastrocnemius and soleus muscles, with relative sparing of rectus femoris and biceps femoris reported in dermatomyositis and IBM

●● associated features include: ● oedema in a myofascial distribution around involved muscle groups, seen more frequently in

dermatomyositis495 ● skin changes, including thickening of subcutaneous tissues with an abnormal reticular pattern

(Fig. 8.169b) ● fatty infiltration, indicative of chronic disease that is unresponsive to treatment and may be followed by

muscle atrophy (Fig. 8.169c) is most prevalent in IBM, while isolated muscle inflammation without fatty infiltration is more suggestive of dermatomyositis and polymyositis496

● soft-tissue calcification rarely occurs and may appear as foci of signal void

●● contrast enhanced FS T1W images have a similar sensitivity to STIR and FS T2W sequences in the detection of muscle inflammation496

●● DTI imaging reveals a higher ADC value in affected muscles, when compared to those of healthy control subjects497

●● focal myositis: is a very rare, benign inflammatory pseudotumour of unknown aetiology, and is selflimiting: ●● it most commonly affects the muscles of the lower limbs, involving the thigh in 50% and calf in 25%,

and multiple muscle involvement may be seen ●● the age range for reported cases varies from 10 to 67 years ●● clinically: it presents as a rapidly growing, painful soft-tissue mass that can mimic a sarcoma, with

spontaneous regression occurring over a period of months to years, but recurrence or progression to a generalised inflammatory myopathy such as polymyositis is recognised

●● unilateral hypertrophy of the tensor fascia lata:500 is also described and may present as a tumour, although it is a benign condition requiring no specific treatment: ●● pathologically: it represents a non-inflammatory/necrotising myopathic process with hypertrophied

muscle ●● recognition of the condition and its specific imaging appearances allows a diagnosis to be made without

the need for biopsy ●● rarely, it may be bilateral

●● unilateral hypertrophy of the calf: due to focal inflammatory myositis of the gastrocnemius secondary to denervation from chronic S1 radiculopathy has also been described501

●● MRI findings: ●● focal myositis: an ovoid/fusiform intramuscular mass measuring 2-10 cm in size and associated with

diffuse muscle oedema: ● lesions are typically isointense (Fig. 8.170a) or slightly hypointense to normal muscle on T1W

images (with T1W hyperintensity occasionally reported), and hyperintense on T2W/STIR images (Fig. 8.170b)

● contrast enhancement may be homogeneous or heterogeneous, with a slow enhancement curve on DCE MRI sequences, in keeping with a benign soft-tissue lesion, although soft-tissue lymphoma may result in similar imaging features

● alternatively, diffuse muscle swelling with hyperintensity on T2W/STIR images surrounding the pseudotumour may be seen

● oedema can involve the deep fascia and subcutaneous fat (Fig. 8.170b), in addition to the affected muscle

● T2W/STIR hyperintensity is usually homogeneous, but may be heterogeneous or have a striped appearance

●● TFL: hypertrophy can be unilateral or bilateral, the muscle bulk increased due to hypertrophy of muscle fibres and intermuscular fat deposition, but muscle SI is normal with no oedema (Figs 8.170c, d)

●● gastrocnemius hypertrophy: diffuse muscle enlargement with increased T1W SI due to fatty replacement and increased STIR SI due to oedema (Fig. 8.170e)

●● DMI: is a rare spontaneous, aseptic complication of diabetes, which presents with the acute onset of painful swelling of the affected muscle, and occasionally forming a palpable mass, but without redness or systemic signs of infection

●● the pain that occurs in DMI is typically more severe than that seen in the autoimmune inflammatory myopathies, in which muscle weakness is a more prominent presenting symptom

●● the condition is more common in women (>60%), with a mean age at presentation of ~42 years and may occur in both type 1 (more commonly) and poorly controlled type 2 diabetes

●● the mean time from onset of diabetes to the first episode of DMI is ~14 years and most patients have multiple complications of diabetes, including peripheral vascular disease and nephropathy

●● the commonest sites of involvement are the thigh (especially the quadriceps) in >80% of cases and the calf in ~20% with the condition being bilateral in 8-30%, the upper limb being rarely involved

●● lesions generally regress spontaneously, but there is a 45% recurrence rate, particularly in cases that have been treated surgically

●● MRI findings: ●● the primary finding is one of muscle inflammation with isointense or reduced SI on T1W images and

heterogeneous hyperintensity on T2W and STIR images (Fig. 8.171a) ●● the muscles appear bulky, with loss of intramuscular fatty septa ●● foci of T1W hyperintensity may be seen due to haemorrhage ●● areas of muscle inflammation enhance following contrast, and rim enhancement around areas of necrotic

muscle is also seen ●● additional features include: diffuse muscle enlargement with loss of muscle margins (Fig. 8.171b) and

fluid in the perimuscular soft tissues, perifascial and subcutaneous oedema (Fig. 8.171c) ●● post-contrast imaging reveals diffuse heterogeneous enhancement, with rim enhancement around

non-enhancing necrotic areas

●● calcific myonecrosis: is a rare, late complication of lower limb trauma, with nearly all reported cases affecting the calf

●● predisposing conditions include compartment syndrome, peroneal nerve injury and severe lower limb trauma

●● clinically: patients present with a slowly enlarging, painless mass, the mean age at presentation being 51 years and the mean time from injury to presentation being 37 years

●● the mass may be limited to a single anatomical compartment or involve the whole calf ●● a thick, nodular hypointense rim is seen on all pulse sequences due to peripheral calcification

(Figs 8.172a-c) ●● on T1W images, the contents of the mass may be isointense, hyperintense or hypointense to skeletal

muscle, with proteinaceous tissue and acute or subacute intralesional haemorrhage resulting in increased T1W signal intensity

●● the contents of the lesion are mainly intermediate SI on T2W images with only small areas of fluid SI, although fluid levels may be present, and no enhancement is seen following contrast

●● the calcific nature of the lesion is best characterised with CT (Fig. 8.172d)

●● neuropathy: results in muscle denervation, which may be occult on MRI performed within the first few weeks (acute denervation), but manifests as increased muscle SI (oedema-like pattern) on FS T2W FSE/STIR images between 1 month to 1 year (subacute stage), being maximal at 6 months: ●● rarely, acute denervation may manifest within 2-4 days ●● the chronic stage of muscle denervation results in atrophy and fatty replacement, which is irreversible,

while muscle hypertrophy is a rare occurrence ●● potential causes of denervation include: spinal cord injury, poliomyelitis, peripheral nerve injury or

compression, and primary neuritis ●● other disorders: resulting in muscle atrophy and fatty replacement include Duchenne muscular dystrophy

(DMD) and Charcot Marie Tooth disease (CMT): ●● DMD:514-516 is an X-linked recessive disorder that results in sarcolemmal fragility, secondary

inflammation and fragility of muscle fibres, with fatty atrophy and fibrotic replacement of affected muscles resulting in progressive weakness, with survival until the early 20s

●● CMT:517,518 represents the most common inherited neuromuscular disease (prevalence 1/2500), resulting in progressive denervation and fatty replacement of skeletal muscles, typically affecting the lower limbs, although upper limbs may also be involved in later stages of the disease:

● several forms of CMT are recognised, including type 1 (demyelinating), with the myelin sheath mainly affected, and type 2 (axonal), resulting in axonal degeneration

● musculoskeletal manifestations include foot drop, hammer toes, pes planus or cavus, hip subluxation and scoliosis

● patients also complain of reduced sensation ●● MRI mapping of nerve injury or compression involves localising the site of the pathology based on

the pattern of muscle denervation changes511 ●● MRI findings:

●● subacute denervation: appears as diffuse muscle oedema with increased muscle SI on FS T2W FSE/STIR images (Figs 8.173a, b) and a normal appearance on T1W images

●● chronic denervation: appears as muscle atrophy and fatty infiltration resulting in increased muscle SI on T1W (Fig. 8.173c) and T2W FSE images, with reduced muscle SI on fat suppression sequences

●● following surgical re-innervation, STIR SI of the re-innervated muscle returns to normal often within several months, while denervated muscle is commonly still hyperintense to normal muscle at 1 year512

●● contrast enhancement of the denervated muscle may commonly be seen in the acute and subacute phases ●● DMD and CMT:519 manifest as progressive fatty replacement of muscles over time, best demonstrated on

T1W/PDW SE sequences (Figs 8.173d, e), while 1H-MR spectroscopy and calculation of muscle to fat fraction are proving useful as quantitative means of evaluating disease progression

●● fatty replacement in DMD progresses most rapidly in the rectus femoris, the long head of biceps femoris and vastus lateralis, and as a result these are the target muscles for serial MR studies during the course of the disease

●● in CMT: muscle atrophy and fatty replacement progresses proximally, with the lower legs and feet most severely affected, and initially denervation oedema is seen, followed by fatty replacement of muscles, with the tibialis anterior often most severely affected

●● spinal nerve roots in CMT are frequently hypertrophied, with an ‘onion bulb’ appearance, and MR neurography findings include T1W hypointense, T2W hyperintense fusiform symmetrical enlargement of peripheral nerves and/or the cauda equina, although type 2 (axonal type) CMT is characterised more by abnormal neural SI than neural enlargement

●● rhabdomyolysis: represents a severe form of skeletal muscle injury characterised by the loss of integrity of muscle cell membranes

●● aetiological factors: include trauma (including severe exercise), ischaemia, burns and toxins, intravenous heparin therapy, statin use and autoimmune inflammation

●● the disorder may result in renal failure (from myoglobinuria), tetany and compartment syndrome ●● MRI findings:

●● initially, there is oedema throughout the affected muscles, with the severity of SI changes correlating with severity of the injury

●● mild cases may resolve, while severe cases may progress to myonecrosis

●● peripheral nerve anatomy: individual nerve fibres are composed of conducting axons, insulating Schwann cells and a supporting connective tissue matrix: ●● each nerve fibre is embedded within connective tissue termed the endoneurium, which is then surrounded

by the perineurium ●● the perineurium divides nerves into individual fascicles, which are the smallest components of the

peripheral nerve that can be visualised at MRI ●● the nerve fascicles are embedded within the interfascicular epineurium, which is then enclosed by

the epineurium, thus comprising a peripheral nerve

●● peripheral nerves: range from 1 to 20 mm in diameter and contain between 1 and 100 fascicles, the size of the nerve determining whether it is visualised at MRI

●● nerves which are routinely seen on high quality clinical MR examinations: include those of the brachial and lumbosacral plexus, the ulnar and median nerves in the arm/forearm/wrist, the radial nerve at the arm/ forearm, the sciatic nerve in the buttock/thigh, the femoral nerve at the groin and the common peroneal/ tibial nerves in the popliteal fossa and proximal calf

●● MRI findings: ●● normal peripheral nerves: appear on sagittal and coronal images as multiple linear structures separated

by fat (Figs 8.174a, b) and on axial imaging as multiple small dots comprising the individual fascicles (Figs 8.174c, d), which are slightly hypointense to muscle on T1W/PDW images (Figs 8.174a, c), isointense or mildly hyperintense to muscle on FS PDW/T2W FSE/STIR (Figs 8.174b, d) images and are surrounded by fat SI due to the perineurial and epineurial fat components:

● prominent nerve fascicles appear slightly hyperintense compared to the perineurium and epineurium due to endoneurial fluid

● normal peripheral nerves should not enhance on post-contrast imaging ●● pathology of the peripheral nerves can result in changes in fascicular architecture and alteration of nerve SI:

● enlargement of a nerve, particularly focal enlargement is considered abnormal ● an altered fascicular pattern, such as inability to resolve individual fascicles in large nerves (e.g. the

sciatic nerve) (Fig. 8.175a), or a non-uniform fascicular pattern (such as clumping of the fascicles or irregular size of individual fascicles) is also considered pathological

● hyperintensity of the nerve on T2W images, most reliably assessed on FS PDW/T2W FSE/STIR (Figs 8.175b, c), is also abnormal

●● MR neurography: is a specific MR protocol for imaging the peripheral nerves, involving high resolution T2W imaging, with fat and fluid suppression: ●● care must be taken to ensure that the orientation of peripheral nerves to the magnetic field does not result

in magic angle artefact ●● nerve fascicles return a high SI due to the endoneurial fluid, and all non-neural structures, including

the epineurium are hypointense ●● diffusion tensor imaging (DTI) and tractography: determine the architectural integrity and orientation

of nerve fibres by interrogating the molecular motion of water, quantified as ADC and fractional anisotropy: ●● it requires a SE single shot DWI echoplanar sequence with FS in the axial plane and perpendicular to

the long axis of the nerve ●● tractography has clinical applications in the investigation of entrapment neuropathies, and has potential in

the monitoring of nerve re-growth after nerve injury

Upper Limb ●● proximal radial nerve compression: the radial nerve is the major continuation of the posterior cord of the

brachial plexus, and may be compressed in the upper arm at the mid-humeral diaphyseal level while running in the spiral groove: ●● clinically: patients present with weakness of triceps, brachioradialis and the extensor and supinator muscles

of the hand and wrist ●● the radial nerve may also be damaged following a humeral diaphyseal fracture or sleep palsy

●● anterior interosseous nerve (AIN) compression: the AIN is the largest branch of the median nerve, arising 2-8 cm distal to the medial epicondyle and continuing distally within pronator teres to eventually run anterior to the interosseous membrane (Fig. 8.9): ●● it is a purely motor nerve, which supplies flexor pollicis longus (FPL), the radial belly of flexor digitorum

profundus (FDP) and the pronator quadratus (PQ) muscles ●● AIN syndrome: also known as Kiloh-Nevin syndrome, manifests clinically as pain and weakness of FPL,

flexor profundus of the index finger and PQ, without sensory deficit, and may simulate flexor tendon rupture ●● compression sites of the AIN include: a fibrous band deep to the ulnar head of pronator teres,

the tendinous origin of the FDS muscle and anomalous vessels, fibrous bands and accessory muscles ●● the nerve may also be injured by direct trauma/laceration and fracture ●● some cases appear to be spontaneous, resolving with conservative treatment, and are thought to be

secondary to AIN neuritis ●● MRI findings:

●● AIN compression: denervation oedema/atrophy of radial half of FDP, FPL and PQ muscles in various combinations (Figs 8.176a, b) with demonstration of intact FDP and FPL tendons

●● femoral nerve compression: most frequently occurs within the iliacus compartment, at the inguinal ligament and the iliopsoas groove, resulting in weak hip flexion and a reduced knee jerk: ●● most femoral nerve entrapment neuropathies are the result of an iliopsoas tear, mass or haematoma, or less

frequently a distended iliopsoas bursa, while nerve injury from hernia repair and arterial puncture may also occur

●● MRI findings: ●● denervation changes are seen in the quadriceps, iliacus, pectineus and sartorius muscles (Figs 8.177a, b)

●● obturator nerve compression: may occur against the lateral pelvic wall secondary to surgery (including total hip replacement), trauma, haematoma, hernia or tumour, resulting in groin pain and reduced adduction and internal rotation of the hip

●● MRI findings: ●● denervation changes occur in the adductor compartment

●● sciatic nerve compression: may occur from piriformis syndrome (piriformis hypertrophy, spasm, inflammation, contracture or scarring) or obturator internus muscle syndrome, resulting in weak knee flexion, poor lower leg control and sensory changes

●● MRI findings: ●● denervation changes are seen in the hamstring compartment and there is also partial involvement of

the AdM ●● lateral cutaneous nerve of thigh compression: usually due to tight fitting clothes, seatbelt, tool belts or

obesity, and less commonly acetabular fractures, ASIS avulsions or sartorius tendon tears, the nerve usually compressed against the inguinal ligament, resulting in reduced sensation and paraesthesia of the anterolateral thigh

●● MRI findings: ●● after exclusion or identification of a potential causative factor, MRI studies are usually unremarkable,

due to the small size of the nerve

●● tibial nerve compression: is uncommon and may follow Baker’s cyst formation, trauma and nerve sheath tumour, and affects the gastrocnemius, tibialis posterior, soleus, FDL and FHL muscles

●● common peroneal nerve compression: may occur following direct trauma, dislocation of the knee, fibular fracture, ganglion cyst formation (intraneural or proximal tibiofibular joint), lateral meniscal cyst formation, a tight plaster cast, repetitive inversion/pronation of the foot, repetitive flexion/extension of the knee and squatting: ●● clinically: compression of the nerve in the peroneal tunnel results in pain along the sensory dermatome of the

common peroneal nerve (CPN), which may mimic a tibial stress fracture, shin splints or compartment syndrome ●● however, nerve compression is characterised by exacerbation of symptoms from inversion and/or plantar

flexion of the foot ●● eventually, foot drop may develop due to denervation of the foot extensors

●● MRI findings: ●● denervation/atrophy of the muscles supplied by the peroneal nerve branches:

● involvement of the tibialis anterior (TA), extensor hallucis longus (EHL) and extensor digitorum (ED) muscles, if the deep ramus is affected

● involvement of the peroneus longus (PL) muscle if the superficial ramus is affected and a combination of the above if both branches are affected (Figs 8.177c-e)

● L5 radiculopathy pattern: tibialis posterior and popliteus, in addition to TA, ED and PL ● non-specific pattern: a mixed pattern including some of the above muscles together with portions of

the gastrocnemius or soleus muscles ● the underlying cause, such as a ganglion cyst

●● benign neurogenic tumours: include schwannoma, neurofibroma and perineurioma ●● malignant neurogenic tumours: include malignant peripheral nerve sheath tumour (MPNST)

●● schwannoma: most commonly affects patients between 20 and 30 years of age and accounts for~5% of all benign soft-tissue tumours

●● commonly involved sites include the spinal and sympathetic nerve roots of the head and neck, the nerves of the flexor compartments of the upper and lower limbs (particularly the ulnar and peroneal nerves)

●● schwannoma: is usually solitary, small (<5 cm) and not associated with NF1, although ~5% of multiple schwannomas are associated with NF1

●● the presence of multiple schwannomas with no evidence of either NF1 or NF2, and no involvement of the 8th cranial nerve is termed schwannomatosis and is considered a distinct clinical entity,530 being reported in 2.4-5% of patients undergoing surgery for schwannoma removal: ●● in ~33% of cases, the multiple schwannomas are limited to a single limb or segment of the spine ●● the Carney complex: is an autosomal dominant condition comprising spotty skin pigmentation, myxomas

and endocrine tumours ●● pathologically: the tumour is oval and related eccentrically to the nerve of origin, with nerve fibres splayed around it:

●● large tumours commonly undergo cystic degeneration, calcification, haemorrhage and fibrosis and are then referred to as ancient schwannomas531

●● schwannomas are well-defined and fusiform/oval in shape, with their long axis running parallel to the long axis of the nerve of origin (Figs 8.178a, b)

●● they are typically homogeneous and isointense to muscle on T1W images (Fig. 8.178a) and hyperintense on T2W FSE (Fig. 8.178b), T2W GRE and FS/STIR images (Fig. 8.178c)

●● the ‘target sign’: is a classical feature of benign peripheral nerve sheath tumours (PNST) and is seen on T2W FSE images as a region of reduced central SI and a peripheral rim of hyperintensity (Fig. 8.178d):

● the ‘target sign’ and a peripheral hyperintense rim are reported in 15% and 58% of schwannomas respectively ● the central area represents fibrous tissue, with a myxoid zone located more peripherally

●● the ‘fascicular sign’: reported in 63% of schwannomas, represents multiple small ring-like structures with peripheral hyperintensity seen on axial T2W and PDW images and is also classical of benign PNSTs (Fig. 8.178c)

●● the ‘split fat sign’: represents a rim of fat around the lesion and is best appreciated on longitudinal T1W images: ● it implies that the lesion arises in an intermuscular location adjacent to the neurovascular bundle, and is

most commonly associated with benign PNSTs (Fig. 8.178e) ●● nerve entering and exiting sign: for lesions arising from major nerves, the nerve may be identified entering

and exiting the tumour (Fig. 8.178f), but this is not seen with intramuscular lesions ●● muscle atrophy in the area supplied by the nerve may also be demonstrated ●● following contrast, enhancement is variable and may be either diffuse (67% of cases) (Figs 8.178g, h) or

peripheral, although lesions demonstrating the target sign may enhance more centrally ●● schwannoma versus neurofibroma:533

● may be differentiated by their relationship to the nerve of origin, with schwannoma being eccentrically related (Fig. 8.178i), although this finding is not particularly reliable532,534

● schwannomas are encapsulated, while most neurofibromas are not ● the fascicular sign is more commonly seen in schwannoma than neurofibroma, and represents enlarged

fascicular bundles ● cystic change, cavitation and calcification is more common in schwannomas, particularly intraspinal lesions ● contrast enhancement patterns may vary between schwannoma and neurofibroma, but a consistent

pattern for each lesion type has not been established ● the target sign occurs in neurofibroma and schwannoma, and is only rarely seen in MPNST

●● schwannomatosis:529,535 the multiple tumours of schwannomatosis have no distinguishing features from isolated schwannomas, other than being more likely to have a homogeneous SI rather than a target-like appearance (Figs 8.179a, b):

● occasionally, multiple lesions can involve a single nerve (Figs 8.179c, d), which may result in a ‘plexiform schwannoma’ appearance

● plexiform schwannoma usually occurs as a solitary lesion in the subcutaneous tissues and is less commonly located in the deeper soft tissues

●● ancient schwannoma:531 may demonstrate focal haemorrhage (increased T1W SI) and cystic degeneration (increased T2W SI, occasionally with fluid levels), calcification and fibrosis:

● contrast enhancement is located in areas adjacent to degenerative changes and also peripherally, related to the capsule (Figs 8.179e, f )

● ancient schwannomas may be much larger than typical schwannomas

●● neurofibroma: also commonly affects patients aged 20-30 years and represents 5-7% of benign soft-tissue tumours, being much more commonly associated with NF1

●● 3 types are described: localised, diffuse and plexiform ●● localised neurofibroma: accounts for ~90% of cases, typically being solitary and not associated with NF1:

●● the majority arise from superficial cutaneous nerves, although deep lesions can also occur when larger nerves are involved

●● they are usually <5 cm in size and fusiform due to the entering and exiting nerve, which tends to lie centrally in relation to the tumour

●● in the context of NF1, neurofibromas are typically larger, deeper and multiple, and malignant change in the absence of NF1 is very rare

●● diffuse neurofibroma:536 primarily affects children and young adults, most commonly affecting the subcutaneous tissues of the head and neck, resulting in diffuse plaque-like skin thickening: ●● most are not associated with NF1 ●● pathologically: it appears as a poorly-defined subcutaneous mass that infiltrates along connective tissue septa

●● plexiform neurofibroma: is essentially pathognomonic of NF1, with the lesions usually developing in early childhood: ●● pathologically: plexiform neurofibroma represents diffuse involvement of a long nerve segment and its

branches with tortuous expansion ●● they may be associated with massive enlargement of an extremity, a condition termed elephantiasis

●● localised neurofibroma: the lesion has the same features as a solitary schwannoma, but may be differentiated by having a central (42%), rather than a peripheral (58%) relationship to the nerve of origin (Figs 8.180a-c):

● other features include: the ‘target sign’ (58%), central enhancement (75%), the ‘fascicular’ sign (25%) (Fig. 8.180d) and a thin T2W hyperintense rim (8%)

● the muscle innervated by the affected nerve may be atrophied and/or striated due to an increased fat content, and may demonstrate denervation oedema, findings which may be subtle and require comparison with the contralateral limb

●● diffuse neurofibroma:536 appears as a reticulated, linear branching structure within the subcutaneous tissues, replacing the fat (Figs 8.180e-g):

● infiltration of the connective tissue septa results in a honeycomb appearance ● the lesions may show reduced SI on T2W images due to their high collagen content

●● plexiform neurofibroma: appears as a serpentine ‘bag of worms’ due to diffuse thickening of the involved nerve and its branches (Figs 8.181a, b):

● may be associated with bone erosion (Figs 8.181c, d) and dysplasia of NF1 (Figs 8.181e, f ) and can result in gross expansion of a whole limb

●● perineurioma: is a rare benign nerve tumour composed of cells that resemble the normal perineurium and may be classified as intraneural, extraneural (soft-tissue perineurioma) or sclerosing

●● extraneural perineurioma: can be divided into spindle cell, sclerosing, reticular and plexiform subtypes, with the majority occurring in the skin and subcutaneous tissues of the trunk and extremities: ●● they typically present in middle-age with no significant male to female ratio

●● intraneural perineurioma: represents whorls of perineurial cells surrounding nerve fibres within a peripheral nerve, usually presenting as progressive mononeuropathy causing loss of motor function in teenagers or young adults: ●● larger nerves tend to be involved including the sciatic nerve, brachial plexus, radial and ulnar nerves in

descending frequency539 ●● lesions have also been reported in the median and trigeminal nerves, the lumbosacral plexus, and rarely as

cutaneous tumours ●● tumour size may reach 20 cm

●● MRI findings: ●● a non-specific focal nerve tumour (Figs 8.182a, b) ●● intraneural perineurioma is typically fusiform in morphology, isointense on T1W, hyperintense on T2W,

with contrast enhancement539 ●● the fascicular architecture is maintained on MR neurography, with enlarged fascicles giving a

honeycomb-like appearance ●● sclerosing perineurioma presents as a subcutaneous mass that may have particularly low SI on T2W images

●● MPNST: accounts for 5-10% of all malignant soft-tissue tumours and usually presents in the 20-50 year age group

●● the diagnosis is suggested when rapid growth occurs in a previously stable neural lesion ●● 25-70% of cases are associated with NF1, in which case they present a decade earlier with a male predilection ●● ~11% of MPNSTs arise following radiotherapy, occurring 10-20 years after treatment ●● major nerve trunks are most commonly affected, usually the sciatic nerve, brachial plexus and sacral plexus

●● clinically: presentation is with pain, sensory deficits and motor weakness: ●● palpable lesions are frequently fixed and rapidly increase in size ●● pain at rest, the presence of neurological defects and a relatively short history are helpful clinical

discriminating factors for differentiating between benign PNST and MPNST ●● pathologically: the majority are high-grade sarcomas, while 10-15% contain foci of other tissue types,

including cartilage, bone and rhabdomyosarcoma, and are termed malignant Triton tumours, which co-exist with NF1 in 44-69%

●● MRI findings: ●● fusiform morphology due to the presence of the entering and exiting nerve ●● however, MPNST is more commonly poorly-defined due to tumour extension beyond the epineurium

and may show thickening of the nerve proximally and distally due to tumour infiltration (Figs 8.183a, b)

●● the presence of haemorrhage and necrosis results in heterogeneous SI and non-uniform contrast enhancement, and the target sign is less likely to be present

●● the role of MRI in differentiation of MPNST from non-neurogenic STS has been evaluated542 with features suggestive of MPNST including intermuscular location, relationship to a large nerve, nodular morphology and heterogeneity of SI

●● tractography, DWI and DTI show promise in the differentiation between benign and malignant peripheral nerve sheath tumours543

●● neurolymphoma: (lymphomatous infiltration of peripheral nerves) occurs in <40% of patients with end-stage non-Hodgkin’s disease and presents with painful sensorimotor neuropathy

●● pathologically: it results from enlarged lymph nodes compressing or infiltrating the adjacent nerves or represents primary neurolymphomatosis, which is rare and occurs in patients without a systemic haematological malignancy

●● MRI findings: ●● neurolymphoma: MRI and MR neurography reveals diffuse (Figs 8.183c-e) or nodular thickening of

the affected nerves, with intense enhancement ●● enlarged adjacent lymph nodes are also present in secondary neurolymphoma

●● intraneural ganglia: are cysts occurring within the epineurium of nerves, with ~75% involving the large nerves about the knee (peroneal, tibial) at the level of the fibular head

●● many lesions may actually be intraneural extensions of ganglion cysts from the proximal tibiofibular joint, related to extension of the ganglion along the articular branch of the peroneal nerve

●● clinically: they present with a palpable mass and/or peroneal/tibial nerve dysfunction ●● pathologically: the lesions show myxoid change with a fibrous capsule and occur in the connective tissue

between the nerve and the nerve sheath, resulting in nerve displacement ●● extraneural ganglia: are also recognised, localised in the perineural soft tissues and capable of causing

extrinsic neural compression: ●● the mechanism of formation is thought to be the same as that for intraneural ganglia

●● in a series of 20 patients with intraneural or extraneural cysts adjacent to the proximal tibiofibular joint, all lesions showed articular communication544

●● 12% of cases follow trauma, the ganglia likely to occur following a combination of neural stretching, blunt trauma, capsular and ligamentous disruption547

●● MRI findings: ●● the typical features of a ganglion, being well-defined and lobular ●● relatively hypointense to muscle on T1W images (Fig. 8.184a), hyperintense on PDW images

(Fig. 8.184b), and markedly hyperintense on T2W/STIR images (Fig. 8.184c) ●● identification of the ganglion extending to the proximal tibiofibular joint via the articular branch of

the peroneal nerve is an important observation (Fig. 8.184d) ●● following contrast, the lesion may show septal and rim enhancement ●● delayed direct MR arthrography following exercise may demonstrate late filling of a peroneal nerve

ganglion, indicating its intra-articular origin548 ●● MR neurography reveals the relationship of the cyst with the affected nerve ●● denervation changes may be demonstrated in the anterior compartment calf musculature

(Fig. 8.184d) ●● several MRI signs associated with intra-and extraneural ganglia have been described:

● tail sign: represents a connection between the proximal tibiofibular joint and the ganglion ● transverse limb sign: represents extension of an intraneural ganglion cyst along the articular branch of

the peroneal nerve ● the signet ring sign: represents the intraneural cyst positioned eccentrically within the epineurium,

with secondary displacement of fascicles

●● traumatic neuroma: develops as a non-neoplastic proliferation of axonal tissue at the end of a severed, partially transected or injured nerve, secondary to surgery or trauma

●● clinically: it most commonly presents with pain and a positive Tinel sign, and a soft-tissue mass may also be palpable

●● it most commonly occurs in the thigh or proximal lower leg following amputation, but also frequently affects the radial nerve and brachial plexus

●● traumatic neuromas: are classified as either neuroma in continuity (NIC) or end bulb neuromas, with NIC further divided into spindle neuromas (with an intact perineurium), or lateral neuromas (with a disrupted perineurium): ●● end bulb neuromas: form from disorganised regenerating axons following nerve transection or disruption,

usually occurring 1-12 months post-trauma ●● NIC: are commonly caused by a fibro-inflammatory response to chronic friction

●● MRI findings: ●● end bulb or stump neuromas appear as a focal enlargement of the nerve (Figs 8.185a-c) ●● NIC are typically fusiform in shape and may demonstrate an entering and exiting nerve, being

distinguished from peripheral nerve sheath tumours by the presence of perineural scarring and the absence of a target or split fat sign

●● they have intermediate SI on T1W images (Fig. 8.185a), intermediate/high SI on T2W images, are hyperintense on FS T2W FSE/STIR (Fig. 8.185b) and show variable enhancement following contrast

●● neuromas may demonstrate the ‘fascicular sign’ on axial T2W images

●● neuritis ossificans: represents heterotopic ossification of a peripheral nerve, a rare lesion, which may be related to nerve injury, although many patients do not report any history of trauma

●● pathologically: the lesion resembles myositis ossificans, with central fibrosis and peripheral ossification ●● reported cases have involved the ulnar, median, sciatic, common peroneal, saphenous and tibial nerves ●● MRI findings:

●● isointense or mildly hyperintense on T1W/PDW (Fig. 8.186a), heterogeneous hyperintensity on T2W/STIR (Fig. 8.186b) with variable central contrast enhancement

●● inflammatory change in the surrounding soft tissues (Fig. 8.186c)

●● sarcoidosis: is the commonest inflammatory neuropathy with sarcoid granulomas involving the nerve diffusely, resulting in either a focal or multi-focal neuropathy: ●● lesions may be bilateral but are usually asynchronous

●● inflammatory pseudotumour:555 is a rare condition of unknown aetiology, being composed of chronic inflammatory and reactive mesenchymal cells: ●● the affected nerve is enlarged, either in a fusiform or nodular fashion

●● leprosy: leprous neuropathy is characterised by the involvement of dermal nerves and superficial peripheral nerve trunks: ●● affected nerves may be locally enlarged or develop abscesses ●● the most commonly affected are the ulnar nerve at the elbow, the median nerve proximal to the carpal

tunnel, the common peroneal nerve at the lateral aspect of the knee, and the tibial nerve at the ankle ●● pathologically: fusiform enlargement of nerve trunks may occur, more commonly with the tuberculoid

form ●● MRI findings:

●● sarcoidosis:549 fusiform enlargement of the nerve has been described with hypointense SI on T1W, fascicular enlargement proximal and distal to the mass on T2W, and mild enhancement

●● inflammatory pseudotumour:553 has been described as a fusiform enlargement of the nerve with intermediate T1W and increased T2W SI, with irregular enhancement

●● localised hypertrophic neuropathy (LHN): is a rare, acquired, tumour-like condition resulting from Schwann cell hyperplasia/hypertrophy secondary to repeated episodes of demyelination and re-myelination: ●● affected nerves are enlarged, occasionally to a length of 15 cm and a width of 2 cm

●● hypertrophic inflammatory neuropathy (HIN): a rare tumour-like lesion often involving the brachial plexus unilaterally or bilaterally and resulting in a fusiform rounded swelling of the nerve: ●● pathologically: the lesion is similar to LHN but with an additional inflammatory component

●● MRI findings: ●● LHN:553 mild nerve enlargement sequences with loss of the normal fascicular pattern, intermediate T1W

SI, increased T2W/STIR SI with enhancement following gadolinium

The Brachial Plexus MR Imaging of the Brachial Plexus ●● the brachial plexus (BP): is adequately imaged at 1.5T field strength, although there is a preference for brachial

plexus imaging to be performed at 3T, particularly in MR neurography ●● a body coil has the advantage of a large FOV, but suffers from a suboptimal SNR, and a head-neck-spine

phased array, neurovascular array or flexi/surface coils will provide a more satisfactory image quality ●● the relatively superficial location of the BP and the contours of the neck and shoulder region result in soft

tissue and air interfaces which may interfere with homogeneous fat suppression ●● straightening of the cervical lordosis is achieved using padding ●● an appropriate standard BP imaging protocol may include:555-557

●● oblique coronal T1W and FS PDW/T2W/STIR sequences of both sides ●● axial PDW and FS PDW sequences to include the cervical spine and brachial plexus ●● sagittal T1W and T2W sequences of the affected side ●● in the clinical setting of thoracic outlet syndrome, the sagittal images should be repeated with the arm

abducted, and MR angiography is also of value ●● BP MR neurography: utilises FS T2W/STIR and T1W SE sequences

●● GRE bright blood vascular sequences and FS optimise visualisation of the adjacent vessels ●● chemical shift imaging techniques separate the fat and fluid signals ●● hybrid techniques include SPIR and SPAIR sequences, the latter being less susceptible to pulsation artefact

with a higher SNR than STIR ●● as high resolution images are required, a small FOV is used

●● contrast enhanced imaging may be used for neoplastic, infectious or inflammatory lesions and chronic plexopathy, but is generally not used for acute brachial plexus injury

●● advanced sequences: ●● T2W 3D imaging with fat and fluid suppression or 3D steady-state free precession sequences improve

visualisation of intradural nerve roots ●● MR myelography obtains volume acquisitions with multi-planar reconstruction capabilities, and is useful

in the detailed analysis of preganglionic lesions, particularly for identifying avulsed nerve roots and pseudomeningoceles

●● DTI and tractography are not yet in general use, but enable detailed evaluation of nerve fibre integrity

●● the BP is formed from the ventral rami of the C5-T1 nerve roots and supplies sensory and motor innervation to the upper limb: ●● occasionally, the plexus comprises C4-C8 (termed a prefixed plexus) or C6-T2 ( a post-fixed plexus)

●● the BP is formed of roots, trunks, divisions, cords and branches ●● the roots: are located between the anterior and middle scalene muscles (the interscalene triangle, adjacent

to the subclavian artery): ●● the C5-C7 roots are located superior to the artery and the C8-T1 roots lie posterior to the artery

●● the trunks: are formed from the roots at the lateral border of the scalene muscles and run in the supraclavicular fossa, superior and posterior to the subclavian artery: ●● the upper trunk forms from C5-C6, the middle trunk from C7 and the lower trunk from C8-T1

●● the divisions: 6 are formed from bifurcation of the 3 trunks into anterior and posterior divisions ●● the cords: are formed from the 6 divisions between the lateral margin of the 1st rib and the medial border

of the coracoid process: ●● the 3 cords are termed lateral, medial and posterior according to their relationship to the subclavian artery ●● the lateral cord is formed from the anterior divisions of the upper and middle trunks ●● the medial cord is formed from the anterior division of the lower trunk ●● the posterior cord is formed from the three posterior divisions

●● the branches: the 5 terminal branches are formed from the cords at the lateral border of the pectoralis minor muscle: ●● the posterior cord: terminates as the axillary and radial nerves ●● the lateral cord: terminates as the musculocutaneous nerve and contributes to the median nerve ●● the medial cord: terminates as the ulnar nerve and also contributes to the median nerve

●● the surgical anatomy: of the BP classifies it as supraclavicular, retroclavicular and infraclavicular: ●● the supraclavicular plexus includes the roots and trunks ●● the retroclavicular plexus comprises the divisions ●● the infraclavicular plexus comprises the cords and portions of the terminal branches

●● MRI findings: ●● the various portions of the BP are well imaged on a combination of coronal (Figs 8.187a, b), axial and

sagittal images (Figs 8.187c-e) ●● on coronal images, the BP appears as an elongated bundle of fibres running superior, lateral and posterior

to the ‘flow void’ of the subclavian artery (Figs 8.187a-e) ●● the fibres of the plexus are isointense to muscle on T1W images (Fig. 8.187a), being separated

by thin strips of fat, and mildly hyperintense compared to muscle on FS T2W FSE/STIR images (Fig. 8.187b)

●● the roots and trunks can be identified in the plane between the anterior and middle scalene muscles (Figs 8.187b, c)

●● the divisions are identified adjacent to the subclavian artery as they pass posterior to the clavicle (Fig. 8.187d)

●● the cords arise lateral to the 1st rib and are also related to the subclavian/axillary artery (Fig. 8.187e), the lateral cord being anterosuperior, the posterior cord being superoposterior and the medial cord being postero-inferior

●● the terminal branches are difficult to identify on MRI, but terminal branch lesions will likely arise within the axilla

●● MRI features that are suggestive of brachial plexus pathology include: loss of fat around all or part of a plexus component, diffuse or focal enlargement of a component, marked hyperintensity on T2W images (Figs 8.187f, g) and enhancement on FS T1W images:

● however, isolated hyperintensity of the plexus on STIR images may not be abnormal

●● adult BPI: may be classified as open or closed and as direct or traction injuries ●● closed traction injuries: are most commonly due to motorcycle accidents and result from simultaneous

traction of the arm and contralateral displacement of the head

●● open injuries: include gun and stab wounds ●● BPI: may also be classified as pre-or post-ganglionic, depending upon the site of injury in relation to

the dorsal root ganglia (DRG), a distinction that will affect the surgical techniques available to repair the plexus (graft repair, neurolysis, neurotisation, re-implantation)

●● preganglionic injuries: are nerve root avulsions from the cervical cord and may be associated with dural tears resulting in pseudomeningocele formation, an indirect sign of intradural root avulsion: ●● pseudomeningoceles are present in 80% of avulsions, and therefore ~20% of cervical root avulsions occur

without pseudomeningocele formation ●● avulsion of cervical roots may also result in acute cervical cord injury

●● postganglionic injuries: may be supraclavicular (affecting the spinal nerves, trunks or divisions) or infraclavicular (affecting the cords or terminal branches) (Figs 8.188a-c)

●● preganglionic and post-ganglionic injuries often occur together (Figs 8.188d, e), and in the majority of cases multi-level root avulsions are seen

●● isolated infraclavicular plexus injury occurs in 16% of BPI, while 5% of cases affect the supraclavicular plexus alone

●● pseudomeningocele: appears as an elongated fluid collection extending laterally from the neural foramen and with cerebrospinal fluid (CSF) SI on all pulse sequences (Figs 8.189a, b):

● MRI is as accurate as CT myelography for the demonstration of pseudomeningocele, which most commonly occur at the C7 and C8 levels

●● nerve root avulsion: appears as absence of the nerve root within the neural foramen and also displacement of the DRG (Fig. 8.189c):

● the use of an overlapping, thin section coronal oblique T2W MR sequence with the plane parallel to the intervertebral foramen allows assessment of exiting nerve roots (Fig. 8.189d) and root avulsion with equal accuracy compared to CT myelography562

● avulsed nerve roots may be visualised within the pseudomeningocele, or they may be retracted distally, with or without the formation of a nerve retraction ball

● pseudomeningocele formation without nerve root avulsion is rare ●● indirect signs of cervical root avulsion: include the presence of abnormal contrast enhancement or T2W

SI in the paraspinal muscles due to denervation, particularly when involving the multifidus muscle (Figs 8.190a, b) and also the shoulder girdle musculature (Fig. 8.190c):

● contrast enhancement of the rootlet, spinal ganglion or spinal cord surface are also recognised indirect signs of preganglionic neural injury

● occasionally, increased SI due to traumatic oedema (Figs 8.190d, e) or haemorrhage may be seen within the cord at the level of root avulsion, as may intradural (Fig. 8.190f) or extradural haemorrhage (Fig. 8.190g)

●● signs of spinal cord injury following nerve root avulsion: include contralateral spinal cord displacement (Figs 8.188d, e), oedema, syringomyelia and focal haemorrhage/haemosiderin deposition:

● chronic post-traumatic spinal cord changes include myelomalacia and cord atrophy ●● stretch injuries: result in continuous but thickened nerves, demonstrating hypo/isointense T1W and

hyperintense T2W SI (Fig. 8.190h) ●● nerve injury may be partial or complete, with implications regarding surgical planning and long term

prognosis ●● fracture fragments and haematoma formation may be the cause of extrinsic neural compression or

entrapment ●● extraspinal soft-tissue injury: may result in oedema and fibrosis of the plexus and associated muscle trauma

(Figs 8.188d, e) ●● MRI is not reliable at clearly defining the site and severity of post-ganglionic BPI

●● infant BPI: is usually secondary to traction on the brachial plexus during a difficult delivery, occurring in 3/1000 live births

●● obstetric brachial plexus palsy (OBBP): usually involves the post-ganglionic supraclavicular plexus (C5-C7) ●● with growth, secondary nerve injuries may result in muscular contractures, glenohumeral dysplasia and

humeral head subluxation or dislocation ●● surgical exploration of damaged nerves is usually undertaken within the first 18 months of life ●● injury may result in formation of neuromas (often following partial nerve disruption), complete nerve

avulsion and pseudomeningoceles

●● surgical repair: should be carried out within 6 months of the injury ●● nerve grafts: usually used for C5 and C6 roots utilising the sural nerve, sensory branch of the radial nerve,

cutaneous brachial nerve and vascularised ulnar nerve ●● nerve transfers: grafting a healthy nerve onto the injured nerve, with grafts including:

●● external branch of spinal nerve onto the suprascapular nerve ●● long head of triceps nerve onto the anterior branch of axillary nerve ●● ulnar nerve bundle onto the anterior branchial nerve ●● intercostal nerve onto the long head of triceps nerve ●● cutaneous lateral antebrachial nerve onto the dorsal branch of the ulnar nerve ●● contralateral C7 root bundle onto the median or musculocutaneous nerve

●● neurovascularised muscle flap grafts

●● primary BP tumours: may be either neurogenic (benign or malignant) or non-neurogenic (benign or malignant), with ~20% of peripheral nerve tumours arising in the brachial plexus

●● clinically: primary BP tumours present as painless masses, or with varying combinations of paraesthesia, pain and neurological dysfunction: ●● on examination, there may be muscle wasting, weakness and a positive Tinel’s sign ●● features suggestive of MPNST are rest pain, progressive loss of nerve function and tumour growth in

a patient with NF1 ●● the differential diagnosis: of primary BP tumours depends upon the presence of NF1, which occurs in

~30%, and in which case neurofibromas account for >75% of tumours, commonly multiple or plexiform: ●● in the absence of NF1, >50% of lesions are solitary schwannomas ●● the incidence of MPNST is not related to the presence of NF1, with ~11% being related to previous

radiotherapy ●● the commonest benign non-neurogenic primary BP tumours are fibromatosis (~33% of cases)

(Figs 8.191a, b) and lipoma (Fig. 8.191c): ●● fibromatosis typically infiltrates the plexus following involvement of the serratus anterior and scalenus

anterior muscles ●● malignant primary BP tumours: include post-radiation sarcoma (PRS), synovial sarcoma (Figs 8.191d, e)

and lymphoma, which can involve the plexus in 2 ways: ●● firstly: compression of the plexus by enlarged lymph nodes, with cervical and supraclavicular nodes

involving the upper plexus (C5-C6) and mediastinal/axillary nodes involving the lower plexus (C7-T1) (Fig. 8.191f):

● the BP is involved in 5-15% of patients with Hodgkin’s lymphoma ● perineural spread of lymphoma may result in epidural and intradural extension

●● secondly: neurolymphomatosis, a rare manifestation of lymphoma that primarily involves the peripheral nerves and results in diffuse thickening of the plexus

●● with regard to surgical management, the following issues are of importance: ●● the differentiation between neurofibroma and schwannoma ●● the proximal intraneural/intraspinal/intradural extension of MPNST, which may result in the lesion

being incurable by surgery ●● the relationship of any lesion to the ipsilateral vertebral artery

●● MRI findings: ●● the MR appearances of the various lesions are identical to those seen with non-BP tumours (as described

previously) ●● the diagnosis of a tumour arising from the plexus, as opposed to other tumours arising in the neck depends

on various factors: ● a tumour involving the roots or trunks will lie in the plane between the anterior and middle scalene

muscles (Figs 8.192a, b)

● since neurofibromas and schwannomas tend to be oval with their long axis orientated to the nerve of origin, lesions arising from the upper roots will lie in an oblique plane from superomedial to inferolateral (Fig. 8.192c), whereas lesions arising from the inferior roots will lie in a horizontal plane (Fig. 8.192d)

● tumours arising from the retroclavicular and infraclavicular plexus will run in an oblique direction from superomedial to inferolateral (Fig. 8.192e)

● proximal intraspinal extension may result in well-defined neural foraminal enlargement (Figs 8.192f, g) and scalloping of the posterolateral vertebral body

● in the setting of NF1, neurofibromas may be multiple and result in diffuse involvement of the BP (Figs 8.193a, b), or present as plexiform lesions (Figs 8.193c-e)

●● Pancoast tumour: refers to a primary lung carcinoma arising in the superior pulmonary sulcus, which may invade the BP (usually the lower trunk) and subclavian vessels: ●● it results in Pancoast’s syndrome: shoulder pain and pain in the C8-T1 distribution, muscle atrophy in

the hand, and Horner’s syndrome (20% of cases) ●● metastatic involvement: supraclavicular or axillary lymphadenopathy from breast cancer may secondarily

involve the BP (usually the medial cord), resulting in neurovascular compromise: ●● true haematogenous metastases to the BP are rare ●● breast carcinoma is the most frequent cause of brachial plexus metastatic disease since lymphatic drainage

involves the axilla568

●● MRI findings: ●● Pancoast tumour: an apical lung mass, commonly with adjacent bone destruction and involvement of

the inferior roots of the BP ●● metastatic lymph node (LN) involvement: intermediate T1W SI and heterogeneous intermediate/

increased T2W SI mass in the supraclavicular fossa or axilla ●● melanoma metastases may appear relatively hyperintense on T1W (Figs 8.194a, b)

●● radiotherapy (RT): is the commonest inflammatory lesion of the BP, usually occurring from treatment to the axillary LN for breast carcinoma

●● neurological symptoms usually manifest 5-30 months post-treatment, with the longest post-radiation interval reported as 20 years, peaking at 10-20 months with dose-related symptom severity

●● certain conditions predispose to post-radiation fibrosis, including Marfan’s syndrome ●● clinically: 3 patterns of radiation fibrosis are described:

●● delayed progressive radiation fibrosis: most likely occurs in patients who have received in excess of 60 Gy and results in fibrosis of the plexus with associated Wallerian degeneration:

● symptoms include paraesthesia, hyperaesthesia, pain and weakness, usually involving the upper trunk distribution, with weakness of arm flexors and shoulder abduction

● the reported incidence is 5-9% and symptoms usually occur within the first year post-treatment

●● reversible (transient) plexopathy: occurs at a median time of 4.5 months post-treatment, with symptoms consisting mainly of paraesthesia and completely resolving in all cases

●● acute ischaemic plexopathy: a very rare occurrence where there is acute plexus ischaemia due to radiation induced subclavian artery occlusion

●● MRI findings: ●● radiation fibrosis: results in diffuse thickening and enhancement of the BP without a focal mass, with low

SI on both T1W and T2W images, although T2W hyperintensity occurs in the acute stages of radiation neuritis

●● in chronic cases, MRI evidence of muscle denervation and the formation of perineural fibrovascular scar tissue may be present

●● differentiation between scar tissue and recurrent tumour may be challenging, but lack of a nodular appearance to the BP, linear BP enhancement and FS T2W/STIR hypointensity favour scar tissue over recurrence

●● thoracic outlet syndrome (TOS): represents a compressive neuropathy/vasculopathy of the brachial plexus and/or subclavian artery/vein, with 3 typical syndromes being described according to the location of BP entrapment: ●● anterior scalene syndrome: refers to compression in the interscalene triangle ●● costo-clavicular syndrome: refers to compression between the clavicle and 1st rib (the costo-clavicular space) ●● retropectoralis minor syndrome: refers to compression deep to the pectoralis minor muscle as it attaches to

the coracoid process (the subcoracoid tunnel) ●● neurovascular compression: occurs most frequently in the costo-clavicular location and least frequently in

the retropectoralis minor space ●● clinically: presentation depends upon whether compression involves only the vessels (vascular TOS), only

the nerves (neurologic TOS) or a combination of both (combined/neurovascular TOS) ●● neurogenic TOS: accounts for up to 69%, venous TOS for up to 66% and arterial TOS in up to 39% of cases,

and causes include congenital bone variations (36%) and congenital fibromuscular anomalies (11%) with cervical spondylosis also contributing: ●● neurogenic TOS is also referred to as cervical rib (and band) syndrome, and is almost always unilateral,

occurring most commonly in women ●● it presents as a chronic lower trunk (C8-T1) plexopathy with wasting of the hand muscles, and sensory

disturbance along the medial arm/forearm with occasional extension into the hand and medial fingers ●● symptoms are exacerbated by hyperabduction and external rotation of the arm ●● the commonest cause is a congenital fibrous band that extends from the first thoracic rib to a cervical rib/

elongated C7 transverse process ●● arterial TOS: involves compression of the subclavian artery, with potential for stenosis, aneurysm, formation

of mural thrombi and subsequent digital ischaemia: ●● patients complain of pain, paraesthesiae and coldness in the hand, but symptoms are frequently absent in

the shoulder region ●● arterial TOS is most frequently caused by a cervical rib or an anomalous rib, the scalene muscle itself,

(through which the subclavian artery may pass), the pectoralis minor tendon and the presence of fibromuscular bands

●● venous TOS: presents with arm swelling, cyanosis, pain and tingling of the fingers and hands secondary to subclavian vein compression, which may be thrombotic or non-thrombotic: ●● it may occur secondary to medical intervention (thrombus following central line placement), or excessive

upper limb activity, the latter termed Paget-Schrotter disease and usually affecting young healthy men ●● MRI findings:

●● distortion/displacement of the plexus by a cervical rib/band (Figs 8.195a, b) has a reported sensitivity and specificity of 79% and 87.5% on conventional MRI in patients with clinical symptoms of TOS:566

● the affected plexus roots may appear slightly oedematous (Fig. 8.195a)

●● changes in the dimension and morphology of the thoracic outlet occur with arm hyperabduction and external rotation in both healthy volunteers and in patients with TOS:573,574

● in TOS, there is a significant reduction of costo-clavicular distance, as measured on sagittal images (Figs 8.195c, d), a significant increase in the width of the subclavius muscle bilaterally as measured on sagittal images, and a significant increase in retropectoralis minor space as measured on sagittal images

● compression of the subclavian vein is commonly seen in both volunteers and patients following arm elevation, but arterial (72%) and neural (7%) compression are only seen in TOS patients

●● reduction of costo-clavicular space is also commonly seen in TOS with the arm in 90° abduction and the patient imaged in an open scanner575

●● vascular TOS: can be demonstrated by MR angiography with the arms in adduction and abduction, the latter position showing stenosis (Fig. 8.195e) or occlusion (Fig. 8.195f) of the subclavian artery576

●● compression of the BP and subclavian artery can also be caused by a hypertrophied scalenus anterior muscle, with/without hypertrophy of the scalenus medius (scalenus anticus syndrome)566