ABSTRACT
NORMAL STRUCTURE AND FUNCTION
into it ●● Composed of four zones: Follicles (B lym-
phocytes), mantle zone (B lymphocytes), paracortex (macrophages, T lymphocytes, dendritic cells), and sinuses (macrophages and antigen-presenting cells)
●● Lymph node biopsy recommended if size >2 cm, abnormal chest x-ray, no signs/symptoms of recent inflammation/infection
TRIAGE OF LYMPH NODE BIOPSY/ASPIRATE
●● Touch preps/smears immediately after lymph node biopsy/aspirate
●● If hematological malignancy, perform flow cytometry, cytogenetics/fluorescence in situ hybridization (FISH) analysis, histology and immunohistochemistry
●● If reactive/Hodgkin lymphoma/metastatic malignancy; cultures, cytogenetic analysis, histology, and immunohistochemistry
Cytogenetic studies
●● Viable fresh tissue used for cultures to prepare metaphase spread
●● Karyotypic abnormalities (diagnostic for certain malignancies) may predict prognosis
●● FISH: Rapid turn-around time, performed on fixed tissue, formalin-fixed paraffinembedded tissue, touch prep, cytospin prep
REACTIVE LYMPHADENOPATHY
●● Follicular hyperplasia/interfollicular hyperplasia
●● Immunoblastic, granulomatous, or histiocytic
Follicular hyperplasias
Non-specific germinal center hyperplasia
cytes, tingible body macrophages, apoptotic cells
●● Follicles mainly in cortex but if severe, may involve paracortex and medulla
HIV-related adenopathy
tine germinal centers ●● Follicular lysis, follicular depletion
Progressively transformed germinal centers
tle zone lymphocytes ●● Absence of variant Reed-Sternberg cells
(d/d from Hodgkin lymphoma)
Toxoplasmosis
encroaching follicular centers ●● Hyperplasia of parasinusoidal monocytoid
B cells
Castleman disease/angiofollicular hyperplasia
●❑ Onion skin mantle zones, multiple germinal centers
●❑ Radially penetrating hyalinized high endothelial venules passing through the germinal centers into the paracortex (lollypops)
●❑ Dense aggregates of follicular dendritic cells highlighted by CD21 and CD23 stains
●❑ Plasma cells are monotypic (lambda positive)
hypergammaglobulinemia ●❑ Follicular hyperplasia, interfollicular
plasmacytosis ●❑ HIV-infected patients; PV-CD associated
with HHV-8 infection
Interfollicular/para-cortical reactions-immunoblastic
Epstein-Barr virus (EBV) infection (infectious mononucleosis)
pressed follicles ●● Expansion of paracortex by immunoblasts,
plasma cells, plasmacytoid lymphocytes, histiocytes
●● Increased number of high endothelial venules
●● B and T immunoblasts highlighted by CD20 and CD3 stains, respectively
membrane protein [LMP] and EBER)
Non-EBV viral adenopathy
Hypersensitivity reactions
●● Dilantin or various vaccines (small pox, measles, tetanus)
●● Distorted architecture, expansion of paracortex (by immunoblasts, lymphocytes, plasma cells, and eosinophils)
Juvenile-onset rheumatoid arthritis
plasma cells, intrasinusoidal neutrophils
Systemic lupus erythematosus
necrosis ●● Necrotic foci show eosinophilic debris,
apoptotic cells, and scant neutrophils/ plasma cells
Histiocytic necrotizing lymphadenitis
now ●● Follicular hyperplasia, para-cortical zonal
karyorrhexis ●● Scant neutrophilic response ●● Paracortex contains small lymphocytes,
immunoblasts, apoptotic debris, plasmacytoid monocytes, high endothelial venules
drome
Autoimmune lymphoproliferative syndrome
●● Lymphadenopathy secondary to Fas or Fas ligand-mediated apoptosis
tosplenomegaly ●● Immunoblasts and T lymphocytes in inter-
follicular region are CD3+ ●● Double-negative T cells ●● Gene sequencing confirms diagnosis
Kawasaki disease
●● Also known as mucocutaneous lymph node syndrome
Granulomatous lymphadenitis
Cat scratch disease
●● Bartonella henselae (small intracellular gramnegative rods)
●● Serpiginous/stellate neutrophil-rich microabscesses in lymph nodes
●● Warthin-Starry stain highlights pleomorphic rods and cocci
●● Polymerase chain reaction (PCR) for diagnostic confirmation
●● Similar histology of lymph nodes seen in Yersinia, tularemia, lymphogranuloma venereum (LGV), Mycobacterium aviumintracellulare (MAI)
Mycobacterial infections
●● Tubercular granulomatous lymphadenitis with caseous necrosis
●● Non-tubercular atypical mycobacterial infection (MAI, Mycobacterium scrofulaceum)
●● Follicular hyperplasia, well-formed epithelioid granulomas, microabscesses
●● Organisms demonstrated by acid-fast stain, auramine orange (fluorescence microscopy), MPT64 Ag (immunochromatographic test), and immunohistochemistry
Chronic granulomatous disease
●● Defective component of NADPH-oxidase pathway
●● Lymph nodes and other tissues infiltrated by granulomas and neutrophil-rich abscesses
●● Superimposed infections by Staphylococcus aureus, Gram-negative bacilli, and Aspergillus
●● Diagnostic tests: Nitroblue tetrazolium reduction, chemiluminescence, flow-cytometry, molecular testing
Histiocytic lymphadenitis
Interfollicular processes with histiocytic proliferation
●● Lymph nodes draining inflammatory/ malignant processes of skin, bowel, lungs
●● Subcapsular/paratrabecular sinuses filled with histiocytes (CD68+ve, S100−ve, CD1a−ve)
●● Compressed follicles with diminutive germinal centers
Sinus histiocytosis with massive lymphadenopathy
and paracortex ●● Sinuses expanded and filled with mixed
infiltrate of lymphocytes, plasma cells, histiocytes, xanthoma cells, and RosaiDorfman histiocytes
●● Emperipolesis: Rosai-Dorfman histiocytes show engulfed lymphocytes in cytoplasm
●● Immunophenotye of Rosai-Dorfman cells: CD68+, S100+, CD21-, and CD1a-
Foreign body sinusoidal histiocytic reactions
prosthesis, contrast media, primary metabolic diseases
●● Lymph nodes draining tumor/ulcerated areas
●● Sinuses distended by foamy macrophages with vacuoles, histiocytes, multinucleated giant cells
Dermatopathic lymphadenitis
sinuses by histiocytes (with melanin/ hemosiderin pigment), Langerhans cells, eosinophils
●● Paracortex is pale pink/mottled due to collections of histiocytes/Langerhans cells
Hemophagocytic lymphohistiocytosis (HLH)
●● Specific clinical, laboratory, and histopathologic criteria required for diagnosis
with phagocytosis)
●● Erythrophagocytosis more common than leukophagocytosis
●● Immunophenotype: CD68+, S100-, CD1a-, and CD207-
Langerhans cell histiocytosis
non-Langerhans histiocytes, dendritic cells, lymphocytes, eosinophils
●● Immunophenotype of Langerhans cells; CD1a+, S100+, CD207+ (Langerin) CD68-
MALIGNANT LYMPHADENOPATHY
Non-Hodgkin lymphoma
●● Nodal malignancies are mostly of lymphoid lineage
●● Four most common pediatric lymphomas are precursor B-cell or T-cell lymphoblastic lymphoma, anaplastic large cell lymphoma, Burkitt lymphoma, and diffuse large B-cell lymphoma
Precursor B lymphoblastic lymphoma
●● Nodal architecture effaced by diffuse proliferation of small/intermediate lymphoblasts
●● Infiltration in capsular collagen, perinodal fat
●● Fine/speckled chromatin, indistinct nucleoli, scant cytoplasm, high mitotic activity
●● Immunophenotype: CD45 (dim to negative), TdT+, CD10+, CD19+, CD20-, sIg-
●● Differential diagnosis with other small blue cell tumors
●● B-cell lymphoblastic lymphoma comprises 15% of lymphoblastic lymphomas
●● T-cell lymphoblastic lymphoma comprises 85% of lymphoblastic lymphomas (commonly involves mediastinum)
Diffuse large B-cell lymphoma
●● Patients have congenital/acquired immune deficiency
●● Steadily enlarging peripheral lymphadenopathy or extra-nodal disease
●● Diffuse growth pattern, abundant cytoplasm
●● Neoplastic lymphocytes mimic reactive immunoblasts or may be frankly anaplastic multilobate cells
●● Immunophenotype: pan B-cell markers (CD19+, CD20+, CD79a+), BCL6+(many), sIg+
Burkitt lymphoma
●● Lymph node architecture distorted by diffuse proliferation of intermediate-size lymphocytes
●● Round/oval nuclei, prominent nucleoli, amphophilic abundant vacuolated cytoplasm, necrosis, high mitotic activity
●● Starry sky appearance (macrophages with cellular debris)
CD19+, CD20+, CD10+, BCL6+, TdT-ve, BCL2-ve
growth/hormonally responsive (jaw, breast, ovaries, testes)
tion, posttransplant ●❑ Visceral involvement (intestines)
T-Lymphoblastic lymphoma
lymphomas ●● Mediastinal involvement (compress heart/
great vessels, pleural/pericardial effusion) ●● Limited bone marrow disease (<25%) ●● Neoplastic lymphocytes have similar mor-
phology to B-lymphoblastic lymphoma ●● Immunophenotype; immature T-cell (CD45
dim/negative, TdT+, cytoplasmic CD3+, surface CD3-, CD2+, CD7+, HLA-DR-, CD10 (positive in 25%)
erogeneous lymphoid population (small/ intermediate/large), scattered infiltrate of eosinophils and plasma cells
●● Neoplastic T-lymphoid cells have irregular nuclei
CD4+, TdT-, CD8-
Anaplastic large cell-lymphoma
soft tissue ●● Neoplastic cells are large, bizarre lobulated
wreath-like nuclei, conspicuous nucleoli, abundant eosinophilic cytoplasm
●● Immunophenotype: CD30+ (membranous and Golgi positive), ALK-1+, EMA+, CD45+, EBER-
Follicular lymphoma
Hodgkin lymphoma
Sternberg (RS) cells (appropriate phenotype) and bland population of background inflammatory cells
ses, mixed cellularity, lymphocyte rich, and lymphocyte depleted)
●● RS cells may be classic type (20-40 µ, multilobed nucleus, large nucleoli, abundant eosinophilic cytoplasm), mononuclear type, or lacunar type (nodular scleroses)
●● Immunophenotype: CD45-, CD30+, CD15±, CD20±, EBER + (50% cases)
Nodular scleroses
lymphadenopathy
cytes, neutrophils, eosinophils, histiocytes ●● RS cells mostly mononuclear, lacunar type
Mixed cellularity
lymphoma and peripheral T-cell lymphoma
Nodular lymphocyte predominant Hodgkin lymphoma
lymphocytes, scattered lymphocytic and histiocytic (L&H) RS cell variants
CD45+, CD20+, OCT-2+ve, BOB.1+ve, CD15-, CD30-, collarette of T cells around L&H cells (CD57+)
Tumors of monocyte/macrophage lineage
●● Chloroma/granulocytic sarcoma (in association with AML)
●● Lymphadenopathy or visceral/soft-tissue mass
●● Lymph node architecture effaced by neoplastic proliferation of intermediate-size cells
●● Myeloblasts have round/oval nuclei, fine chromatin, moderate cytoplasm
●● Cells positive for CD45, myeloperoxidase, Leder stain (chloroacetate esterase)
EMBRYOLOGY
●● Develops from mesenchyme located in dorsal mesogastrium
NORMAL STRUCTURE AND FUNCTION
●● Major site of blood filtration, antigen-antibody reactions, protects against encapsulated bacteria
lets/antibody-coated red cells
White pulp
COMMON CAUSES OF SPLENECTOMY
●● Hereditary spherocytosis, hemolytic anemias, trauma, ITP, hypersplenism
CONGENITAL ANOMALIES
Asplenia
nosis (due to associated defects) ●● Findings in peripheral blood; Howell-Jolly
bodies, Pappenheimer bodies, dysmorphic/ nucleated red blood cells
Polysplenia
Accessory spleen
splenectomy (to prevent recurrence of primary disease)
Fusion
Hamartoma
Cysts
DISEASES OF RED PULP
Congestion
●● Chronic passive congestion in portal hypertension/right-sided heart failure
Thrombocytopenia
●● Refractory thrombocytopenia treated with splenectomy
●● Etiology: Drug induced, virus induced, autoimmune, immunodeficiency related, ITP
histiocytes (containing platelet debris)
Hereditary hemolytic anemias
●● Disorders include hereditary spherocytosis, elliptocytosis, hemoglobinopathies (thalassemias, sickle-cell anemia)
●● Subtotal splenectomy (preserving lower pole) recommended; cures hemolysis, retains spleen function
●● Sickle cell anemia (after 10 years of age); spontaneous autosplenectomy (small and fibrotic spleen, multicolored deposits of minerals/hemosiderin = Gamma-Gandy bodies)
●● Hereditary hemolytic anemias; splenic congestion, extra-medullary hematopoiesis
Infection
●● Acute splenitis; bloodborne bacteria (neutrophilic and plasma cell infiltrate)
●● Granulomatous inflammation; fungal, mycobacterial infections
●● Vascular peliosis; Bartonella henselae in spleen/liver
●● EBV-related infectious mononucleosis; red/ white pulp infiltrated by polymorphous T and B immunoblasts (CD30 + , CD15-, and CD45-), they should be differentiated from RS cells
DISORDERS OF WHITE PULP
Inborn errors of metabolism
Gaucher disease type I
●● Splenic sinuses expanded by clusters/ sheets of large macrophages (Gaucher cells)
●● Nuclei are bland, round/oval, cytoplasm abundant, wrinkled tissue-paper type
somal β-glucocerebrosidase activity ●● Pseudo-Gaucher cells in the spleen; seen in
CML
Niemann-Pick disease
●● Type A (infantile): Severe neurodegenerative disease of infancy
●● Accumulation of storage macrophages with sphingomyelin in spleen/other organs
●● Niemann-Pick cells have vacuolated cytoplasm (staining blue-green with Giemsa stain)
●● Cells positive with PAS and lipid stains but negative with iron stain
Tay-Sachs disease
cytoplasm ●● Stain positive for lipids
Mucopolysaccharidosis
●● Macrophage, endothelial cells, and intimal smooth muscle cells involved
Chediak-Higashi syndrome
cells with giant abnormal granules ●● Oculocutaneous albinism, bleeding abnor-
malities, bacterial infections, neurologic symptoms
Langerhans cell histiocytosis
●● Red pulp infiltrated by neoplastic cells (multisystemic LCH)
Virus-associated hemophagocytic syndrome
●● Red pulp contains erythrophagocytic histiocytes
LEUKEMIA AND MYELOPROLIFERATIVE DISORDERS
●● Splenomegaly most marked in myeloproliferative disorders; chronic myelogenous leukemia and juvenile myelomonocytic leukemia
●● Sheets of immature and maturing myeloid cells in the red pulp
VASCULAR TUMORS
fusely dispersed throughout spleen) lacking endothelial lining
●● Littoral cell angiomas: Benign vascular tumors, sinusoidal spaces lined by tall endothelial cells (endothelial/histiocytic markers expressed)
OTHER NON-HEMATOPOIETIC TUMORS
●● Inflammatory myofibroblastic tumors (positive for SMA, MSA, and cytokeratin)
FOLLICULAR HYPERPLASIA
NON-HODGKIN LYMPHOMA
HODGKIN LYMPHOMA
●● Fibrotic, well-circumscribed gray-tan masses, in white pulp
●● Lymphoepithelial organ located in anterior mediastinum
●● Important role in normal T-cell development and cell-mediated immunity
inferior aspect of third pharyngeal pouch
●● Thymocyte differentiation begins at ninth week of gestation
●● Organization into cortex and medulla begins at 12th week of gestation
ANATOMY AND HISTOLOGY
●● Thymus continues to grow from birth to puberty
●● After puberty it progressively involutes to old age
lymphocytes, mixed population of monocytes, plasma cells, eosinophils, and mature B lymphocytes
●● Cortical lymphocytes express markers of immature T cells
●● Medullary thymocytes express markers of mature peripheral T cells
●● Epithelial cells in cortex and medulla provide stroma/framework for developing thymocytes
●● Hassall corpuscles located in medulla; concentric whorls of keratinized epithelial cells with cystic degeneration
CONGENITAL ANOMALIES
Thymic atrophy
●● Normal aging (replacement of lymphoid tissue by adipocytes)
●● Acquired hypoplasia: Irradiation, cytotoxic drugs, stress, malnourishment (cortex infiltrated by macrophages, starry sky appearance)
Thymic hypoplasia/complete agenesis
DiGeorge anomaly
fourth branchial arches
●● Hypoplasia/aplasia of thymus, hypoplasia of parathyroid glands/hypocalcemia, truncus arteriosus, dysmorphic facies, micrognathia
Severe combined immunodeficiency
●● Infants from an early age prone to lifethreatening viral/fungal infections
●● Depletion of all lymphoid tissue in body, including thymus
THYMIC TUMORS/TUMOR-LIKE CONDITIONS
●● Cysts, thymolipomas, thymic hyperplasia, and thymic tumors
Thymic hyperplasia
●● Associated with autoimmune diseases such as myasthenia gravis
●● Diagnosis of hypertrophy: Thymus must weigh >100 g
Thymic neoplasms
Thymoma
tive for cytokeratin and EMA) ●● Reactive non-neoplastic lymphoid cells
(immature T lymphocytes positive for TdT, CD1, CD2, coexpress CD4 and CD8)
●● Myasthenia gravis/other autoimmune disorders develop in children with thymoma
inant thymoma) ●❑ Type B2 thymoma (mixed lymphoepithe-
lial thymoma) ●❑ Type B3 thymoma (epithelial predomi-
nant thymoma) ●❑ Type C thymoma (thymic carcinoma)—
cells have cytological features of epithelial malignancy
and lymphoblastic lymphomas ●● 80% of non-Hodgkin lymphomas in chil-
dren are T-cell type ●● Most of the mediastinal lymphoblastic lym-
phomas are T-cell lymphomas (arise in thymic remnants)
Lymphoblastic lymphoma ●● Anterior mediastinal mass, cough, chest
pain, dysphagia, dyspnea, superior vena cava syndrome
●● 80%–90% of tumors are T-cell type and express TdT, CD1a, CD2, CD3 (cytoplasmic), CD7, CD43
●● Coexpress CD4 and CD8 or may express neither CD4 nor CD8
●● B-lymphoblastic lymphomas express CD10, TdT, CD19, and no expression of surface immunoglobulin
●● Lymphoblastic lymphoma where lymphoblasts comprise >25% of bone marrow are classified as acute lymphoblastic leukemia
Large-cell lymphoma ●● Young women, symptomatology similar to
lymphoblastic lymphoma in mediastinum ●● Mature B cell (CD19 and CD20 positive) ●● IHC differentiates the neoplasm from semi-
nomas (PLAP+ and LCA-), thymic carcinoma (keratin+ and LCA-), ALCL (AlK+, EMA+, and CD30+), syncytial variant of nodular sclerosis Hodgkin lymphoma (RS cells positive for CD15 and CD30)
Hodgkin lymphoma ●● In mediastinum, common type is nodular
sclerosis ●● Dense bands of collagen in lymph nodes/
thymus
