ABSTRACT
Sonographic examination of the rectum, including the surrounding structures, using intraluminal transducers has become increasingly important in clinical practice. Endorectal ultrasound (ERUS) has been shown to be a useful tool in evaluating anal, rectal and pelvic disorders, due to the high resolution provided. The use of ERUS is recommended for a wide variety of indications, including local staging of rectal tumours. ERUS is usually performed using rigid probes. Alternatively, flexible scopes with an integrated transducer at the tip of the instrument can be used, although examination is a little more tedious and orientation is more difficult. Modern transducers should allow a complete 360° transverse section, which facilitates anatomic mapping and navigation. The internal anal sphincter can regularly be seen as a homogeneous hypoechoic layer with a thickness of 2–4 mm, with no significant sex-dependent difference. The funnel of the levator ani separates the extraperitoneal pelvis into an infraperitoneal or pelvirectal space and a subcutaneous or ischiorectal space.
