Sites of surgical waisting in the abdominoperineal specimen

Background: In the abdominoperineal excision (APE) specimen 'surgical waisting' has been described, where the least amount of tissue covers the rectum. This is associated with high positive margin rates. The aim of this study, was to locate the site of surgical waisting, namely the least amount of tissue excised at APE. Methods: Distances from the anal verge to the distal and proximal edges of the sphincter, puborectalis and levator muscles were measured in 12 patients using morphological features on magnetic resonance images. Distances from the mucularis propria to the outer surface of the pelvic muscles and the outer edge of the specimen were measured on axial images. The height from the anal verge at which axial measurements of tissue were minimal was determined. Results: The presence of a surgical waist between 35 and 42 nun above the anal verge, corresponding to the puborectalis, was confirmed. A smaller amount of perirectal tissue was resected at this level than at other heights (P < 0.001). Conclusion: Because less tissue is excised at the puborectalis, careful dissection along the levator plane is necessary, especially if tumour is present. More radical excision of the levators and puborectalis may, be of benefit in such patients.