Relationship between external anal sphincter atrophy at endoanal magnetic resonance imaging and clinical, functional, and anatomic characteristics in patients with fecal incontinence

PURPOSE: External anal sphincter atrophy at endoanal magnetic resonance imaging has been associated with poor outcome of anal sphincter repair. We studied the relationship between external anal sphincter atrophy on endoanal magnetic resonance imaging and clinical, functional, and anatomic characteristics in patients with fecal incontinence. METHODS: In 200 patients (mean Vaizey score, 18 (+/-2.9 standard deviation)) magnetic resonance images were evaluated for external anal sphincter atrophy (none, mild, or severe) by radiologists blinded to anorectal functional test results and details from medical history. Subgroups of patients with and without atrophy were compared for medical history, anal manometry, pudendal nerve latency testing, anal sensitivity testing, external anal sphincter thickness, and external anal sphincter defects. Whenever significant differences were detected, we tested for differences between patients with mild and severe atrophy. RESULTS: External anal sphincter atrophy was demonstrated in 123 patients (62 percent): graded as mild in 79 (40 percent), and severe in 44 patients (22 percent). Patients with atrophy were more often female (P < 0.001) and older (P = 0.003). They had a lower maximal squeeze (P = 0.01) and squeeze increment pressure (P < 0.001). Patients with severe atrophy had a lower maximal squeeze (P = 0.003) and squeeze increment pressure (P < 0.001) than patients with mild atrophy. These effects were not attenuated by potential confounding variables. Patients with atrophy could not be identified a priori by other characteristics. CONCLUSIONS: External anal sphincter atrophy at endoanal magnetic resonance imaging was depicted in 62 percent of patients, varying from mild to severe. Because increasing levels of atrophy were associated with impaired squeeze function, further studies are needed to evaluate whether grading atrophy is clinically valuable in selecting patients for anal sphincter repai