THE NORMAL AND PATHOLOGICAL ISCHIORECTAL FOSSA AT CT AND MR-IMAGING

A wide spectrum of disease processes involve the ischiorectal fossa, i ncluding congenital and developmental lesions; inflammatory, traumatic , and hemorrhagic conditions; primary tumors; and pathologic processes outside the ischiorectal fossa with secondary involvement. Both compu ted tomography (CT) and magnetic resonance (MR) imaging are useful in the definitive diagnosis of these pathologic conditions, with MR imagi ng being the modality of choice because of its superior contrast resol ution and multiplanar capability. In Gartner duct cyst, both CT and MR imaging demonstrate a well-defined, round mass; in tailgut cyst, CT d emonstrates a well-defined retrorectal mass with a solid or cystic app earance. MR imaging in particular plays a major role in the assessment of fistula in ano, infection, and hematoma. Lipoma and pelvic plexifo rm neurofibroma typically have low attenuation and high signal intensi ty at CT and MR imaging, respectively. Recurrent rectal tumor appears at both modalities as an irregular soft-tissue mass with or without ce ntral necrosis in the presacral space, perineum, or pelvic sidewall. F amiliarity with the imaging features and differential diagnoses of var ious ischiorectal pathologic processes will facilitate prompt, accurat e diagnosis and treatment.