Endoanal MR Imaging of the Anal Sphincter in Fecal Incontinence

Abstract

Fecal incontinence is a major medical and social problem. The most frequent cause is a pathologic condition of the anal sphincter. Endoanal magnetic resonance (MR) imaging allows detailed visualization of the normal anatomy and pathologic conditions of the anal sphincter. The hyperintense internal sphincter appears as a continuation of the smooth muscle of the rectum; the hypointense external sphincter surrounds the lower part of the internal sphincter. 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 defects: a posterior discontinuity (often seen in young male patients) and an anterior discontinuity (often seen in female patients). Atrophy of the external sphincter is easily detected on coronal MR images by comparing the thicknesses of all anal muscles. Endoanal MR imaging is superior to endoanal ultrasonography because of the multiplanar capability and higher inherent contrast resolution of the former. Use of endoanal MR imaging may lead to better selection of candidates for surgery and therefore better surgical results. Endoanal MR imaging is the most accurate technique for detection and characterization of sphincteric lesions and planning of optimal therapy.

Relationship Between External Anal Sphincter Atrophy at Endoanal Magnetic Resonance Imaging and Clinical, Functional, and Anatomic Characteristics in Patients With Fecal Incontinence

“…Additionally, the radiologists evaluated the presence of external anal sphincter atrophy, defined as thinning of the external anal sphincter muscle and/or diffuse replacement of external anal sphincter muscle by fat. 26 Atrophy was graded as none (no thinning and no replacement of sphincter muscle by fat; Fig. 1), mild (<50 percent thinning and/or replacement of sphincter muscle by fat; Fig.…”

“…18 Previous studies have shown that both endoanal sonography and endoanal MRI are accurate tools for mapping internal and external anal sphincter defects. [19][20][21][22][23][24][25][26] External anal sphincter atrophy can only be demonstrated with endoanal MRI. 17,[25][26][27][28][29][30][31][32] This makes endoanal MRI a valuable tool to predict the outcome of anterior anal sphincter repair.…”

“…Most studies evaluating external anal sphincter atrophy at endoanal MRI have reported data about the presence or absence of external anal sphincter atrophy. 17,25,26,[29][30][31][32] Additionally, grading atrophy as ''none,'' ''mild,'' or ''severe'' may further refine the diagnosis of external anal sphincter atrophy and might have an impact on the selection of patients for anterior anal sphincter repair.…”

Anal incontinence: diagnosis by endoanal US or endovaginal MRI

“…Most ruptures of the external sphincter at delivery occur at this weakest area. The external sphincter has been shown to be better evaluated with The dark spot is artefact caused by sutures EAMRI than EAUS; in the present study EVMRI and EAUS were equal [4,15].…”

“…The normal anatomy of the sphincter area as imaged by the endorectal coil is well documented [13][14][15][16]. The resolution of the body coil, more pleasant for the patient, is not sufficient in sphincter imaging [17,18].…”