Endoanal MR imaging of the anal sphincter in fecal incontinence

Fecal incontinence is a major medical and social problem. The most frequent cause is a pathologic condition of the anal sphincter. Endoanal magnetic r esonance (MR) imaging allows detailed visualization of the normal anatomy a nd pathologic conditions of the anal sphincter. The hyperintense internal s phincter appears as a continuation of the smooth muscle of the rectum; the hypointense external sphincter surrounds the lower part of the internal sph incter. A sphincteric defect is seen as a discontinuity of the muscle ring. Scarring appears as a hypointense deformation of the normal pattern of the muscle layer. Two external sphincteric patterns may be misdiagnosed as def ects: a posterior discontinuity (often seen in young male patients) and an anterior discontinuity (often seen in female patients). Atrophy of the exte rnal sphincter is easily detected on coronal MR images by comparing the thi cknesses of all anal muscles. Endoanal MR imaging is superior to endoanal u ltrasonography because of the multiplanar capability and higher inherent co ntrast resolution of the former. Use of endoanal MR imaging may lead to bet ter selection of candidates for surgery and therefore better surgical resul ts. Endoanal MR imaging is the most accurate technique for detection and ch aracterization of sphincteric lesions and planning of optimal therapy.