Wide Variation in Anal Sphincter Muscles in Cases of High- and Intermediate-type Male Anorectal Malformation

Purpose: The distribution of sphincter muscle complex in anorectal malformation (ARM) needs to be investigated on a case-by-case basis. This study was undertaken to demonstrate the differences in the anal sphincter muscles between patients with the same type of ARM. Computed tomography (CT) data from cases of high- and intermediate-type male patients with ARM were reviewed using three-dimensional (3D) image analysis.

Materials And Methods: Twenty-seven male patients with ARM (18 high and 9 intermediate) before anorectoplasty were assessed using multidetector-row helical CT (MRH-CT). A 3D reconstruction was made using volume rendering method. The multi-dimensional sections of the 3D reconstructed images of the pelvic muscles were then analyzed and compared with schematic drawings from the literature.

Results: The sphincters in the high and intermediate types of ARM could be divided into five groups. In 13 out of 18 cases in the high type and 7 out of 9 cases in the intermediate type, images of the sphincter muscles appeared different from schematic drawings appearing in the literature.

Conclusion: In both high and intermediate types of ARM, more than 2/3 of cases demonstrated unexpectedly displaced and deformed hypoplastic sphincters. Therefore, we recommend that variations in anal sphincter should be investigated on an individual basis prior to surgery.