Unexpectedly deformed anal sphincter in low-type anorectal malformation

PurposeThe sphincter muscles in anorectal anomalies, which do not appear in the surgical field, cannot be described adequately. Details of the anal sphincter in low-type anorectal malformations were investigated using 3-dimensional (3D) image analysis.Patients and MethodsThirty patients (10 males and 20 females) with low-type anorectal malformation were investigated with multidetector-row helical computed tomography. An image of the anorectal part was obtained with a slice thickness of 1 mm and a reconstruction pitch of 0.5 mm. A 3D reconstruction on a personal computer was made with a volume rendering method assisted by our own software (NewVES).ResultsVery thin vertical fibers (VFs) were observed behind the fistula in almost half of the low-type cases. They did not wrap the distal end of the fistula. The 3D images of these sphincters were different in each case.DiscussionThe fistula was dislocated forward from the deformed hypoplastic sphincter. We suggest that surgical mobilization of the anorectum into the center of the hypoplastic sphincter would be difficult using the cut back or Potts methods.ConclusionThe choice of surgical method should take into consideration the displaced and deformed hypoplastic anal sphincter.