Gender differences in the longitudinal pressure profile of the anal canal related to anatomical structure as demonstrated on three-dimensional anal endosonography

Background: Anal canal squeeze pressure is assumed to be due to external sp hincter contraction, but the contribution of other muscles has not been exp lored. Methods: Ten male and ten nulliparous female asymptomatic subjects had thre e-dimensional anal endosonography and manometry. Incremental squeeze pressu res at 0.5-cm intervals, expressed as a percentage of the maximum pressure recorded anywhere in the canal, were related to the following anatomical le vels: puborectalis, overlap between external anal sphincter (EAS) and pubor ectalis, external and internal anal sphincters, and external anal sphincter only. Levels were determined by coronal and sagittal endosonographic recon structions. Results: Puborectalis was the same length in men and women (median 23.9 ver sus 27.1 mm) but represented a greater proportion of the anal canal in wome n (45 versus 61 per cent; P = 0.02). At the level of puborectalis alone, th e pressure generated as a proportion of maximum anal canal pressure was 71 (range 32-100) per cent in men and 62 (range 32-100) per cent in women. At the level of the EAS alone, the pressure was 60 (4-98) per cent in men and 82 (41-100) per cent in women; where the external sphincter was overlapped by puborectalis, the pressure was 98 (60-100) per cent in men and 75 (47-10 0) per cent in women. Conclusion: Maximal anal canal squeeze pressure is found where the puborect alis overlaps the EAS. This segment represents a significant proportion of anal canal length in women.