Magnetic resonance imaging of anal sphincters after reconstruction of high or intermediate anorectal anomalies with posterior sagittal anorectoplasy and fistula-preserving technique

Abstract

Background/Purpose: Internal anal sphincter (IAS) function can be expected in approximately 75% of cases of high or intermediate anorectal anomaly reconstruction if the fistula region is preserved and transposed to become the new anal canal. Methods: To investigate the morphology of the IAS structure, magnetic resonance (MR) imaging was performed postoperatively in 14 patients operated on with posterior sagittal anorectoplasty (PSARP) and fistula-preserving technique. The results were compared with the appearance of the anal canal in seven normal children. In addition, comparison was made with the images of five patients operated on with earlier pull-through techniques, in which the fistula region was resected. Results: In all patients operated on with PSARP and fistula-preserving technique, the MRI displayed an IAS-like smooth muscle structure encircling a closed anal canal. In comparison with normal controls, the image of this IAS was more irregular and had greater variations in thickness in different directions. Moreover, the area of the IAS structure was larger in comparison with the controls. Eleven of the 14 patients showed a positive rectoanal inhibition reflex in rectoanal manometry. However, the MR findings of the three cases lacking the reflex were not different compared with the rest of the group. The five patients operated on with earlier techniques demonstrated an open anal canal without a measurable IAS smooth muscle component. Conclusions: An IAS smooth muscle structure was seen by MRI in all patients operated on with PSARP and fistula-preserving technique independently of the severity of the malformation and the postoperative physiological IAS function. However, this structure was in most cases more voluminous and irregular compared with normal controls.