Prospective Assessment of Accuracy of Endoanal MR Imaging and Endosonography in Patients with Fecal Incontinence

Endoanal MR imaging was prospectively compared with anal endosonography to determine any superiority in the characterization of sphincter morphology in fecal incontinence. Fifty-two consecutive patients with fecal incontinence were examined with anal endosonography and endoanal MR imaging after a detailed bowel history, clinical examination, and complete anorectal physiologic testing. External and internal anal sphincter integrity was noted on both endosonograms and MR images by two radiologists in consensus, who read individual scans in a random order to avoid recall bias. Imaging findings were subsequently compared, and arbitration of any disagreement between endosonography and MR imaging was made in consensus by a surgeon and a gastroenterologist who also had access to the patient's history, clinical examination, and anorectal physiologic testing results. Complete agreement was found between anal endosonographic and MR imaging interpretations in 32 patients (62%): 10 with combined external and internal sphincter injuries, two with isolated internal sphincter injury, and 20 with intact sphincters. Of 20 patients in whom results of the scans were disparate, incorrect interpretation was found on endosonography in six patients, on MR imaging in 15. Overall, one error relating to the internal sphincter was made on endosonography versus 12 on MR imaging (p = 0.002), and five errors relating to the external sphincter were made on endosonography versus six on MR imaging (p = 1.0). This study suggests that endoanal sonography and endoanal MR imaging are equivalent in diagnosing external anal sphincter injury, but MR imaging is inferior in diagnosing internal anal sphincter injury.