Morphologic changes of the anal sphincter musculature during and after temporary stool deviation

Background and aims. Temporary stool deviation, using a stoma, is a well-kn own surgical principle to protect low colorectal or coloanal anastomoses. T he purpose of this study was to evaluate any morphologic changes with regar d to the anal sphincter muscles during and after temporary ileostomy. Patie nts and methods: Forty-four patients with rectal carcinomas were studied pr ospectively. All patients underwent low anterior resection. Reconstruction was performed using either a coloanal pouch or a straight end-to-end anasto mosis. A protective stoma was fashioned in all 44 patients (ileostomy n=41; colostomy n=3). Stoma closure was carried out after a median of 85 days (4 1-330 days). Using a standard protocol, anal-sphincter thickness [m. pubore ctalis, external anal sphincter (EAS) and internal anal (IAS) sphincter] wa s assessed by means of endoanal ultrasonography preoperatively, at the time of stoma closure, and every 3 months thereafter for 1 year. Results: The d iameter of the puborectal muscle decreased from a median preoperative value of 6.3 mm to 5.7 mm at the time of stoma closure (P=0.03). After 3 months, 6.2 mm was measured. This value remained stable for the complete follow-up period. Similar results were recorded for the EAS. The IAS thickness remai ned stable throughout the study period, measuring between 2.1 mm and 2.4 mm . Conclusion: Temporary stool deviation does lead to morphologic changes of the anal sphincter. While the smooth muscle remains unchanged, the striate d counterpart undergoes atrophic transformation. However, after passage rec onstruction, i.e., stoma closure, a rapid regeneration of the voluntary mus cles is observed.