MR-IMAGING OF THE ANAL-SPHINCTER IN MULTIPAROUS WOMEN USING AN ENDOANAL COIL - CORRELATION WITH IN-VITRO ANATOMY AND APPEARANCES IN FECAL INCONTINENCE

OBJECTIVE. The aim of this study was to correlate the components of th e normal female anal sphincter seen on high-resolution MR images with the in vitro anatomy and to describe the change in appearances of thes e components in multiparous women with fecal incontinence. SUBJECTS AN D METHODS. Ten asymptomatic female volunteers (32-72 years old; mean, 54 years old) and 22 women with fecal incontinence were studied. In si x patients (26-68 years old; mean, 49 years old) fecal incontinence be gan immediately after childbirth; in the remaining 16 patients (45-77 years old; mean, 58 years old) fecal incontinence developed 15-30 year s after childbirth. In the latter group of patients, terminal motor la tencies of the pudendal nerve were measured. Imaging was done on a 0.5 -T Picker Asset unit and on a 1.0-T Picker HPQ unit. A saddle geometry endoanal receiver coil was used for all imaging. T1-weighted spin-ech o (720-820/20 [range of TR/TE]), T2-weighted spin-echo (2500/80 [TR/TE ]), fast spin-echo (4500/96 [TR/ effective TE]), and short inversion t ime inversion recovery (2500/80 [TRP/TE]; inversion time, 107 msec) MR images were obtained in transverse, coronal oblique, and sagittal pla nes. Images were assessed for integrity of the sphincter components. A nonpaired separate-variance t test was used to compare thickness of i ndividual muscle components between patients with delayed-onset fecal incontinence and asymptomatic age-matched volunteers. Degree of muscle atrophy was correlated with degree of delay in the terminal motor lat ency of the pudendal nerve. RESULTS. The high resolution obtained with an endoanal coil allowed differentiation of the various muscle compon ents of the anal sphincter complex. The internal sphincter was seen as a ring of homogeneously high signal intensity with a low-signal-inten sity rim that was rich in collagen and contained neurovascular bundles . The external anal sphincter, which had low signal intensity on T1- a nd T2-weighted images, was shown as three components: subcutaneous, su perficial, and deep. In six patients who had fecal incontinence that b egan immediately after childbirth, endoanal MR imaging revealed the si te and extent of a tear. All tears were confirmed at surgery. In the 1 6 patients who had fecal incontinence that began several years after c hildbirth, atrophy of the external sphincter was revealed in all cases in the superficial and deep components. The internal sphincter remain ed normal. However, we found that the degree of atrophy of individual components of the external sphincter did not correlate with the degree of delay in pudendal nerve conduction. CONCLUSION. MR imaging with an endoanal coil reveals the integrity and bulk of individual muscle com ponents of the anal sphincter in multiparous women with fecal incontin ence.