Histological Configuration and Nerve Distribution of the Anal Canal/Inferior Part of the Rectum with Special Reference to the Attachment to the Vagina

Abstract

We examined sagittal or nearly horizontal histological sections of the pelvic floor tissues from 10 elderly cadavers. These sections included the anal canal/inferior part of the rectum (inferior rectum) as well as the vagina and its associated tissue. The conjoint longitudinal muscle coat, which was rich in elastic fibers, ran inferiorly between the lateral extension of the perineal body (LEPB) and the internal anal sphincter and the end of the external anal sphincter. The longitudinal muscle coat often divided into two bundles and the anterior one ended at the LEPB. Because the rectovaginal septum or fascia was thin and fragmented, the longitudinal muscle coat was a limited, constant plate-like structure interposed between the anal canal and vagina. In the anterior and anterolateral side of the anal canal/inferior rectum, the highest nerve density was seen along the vaginal wall: most of them appeared to run obliquely to the supero-inferior axis. Likewise, the paracolpium contained abundant nerves running almost along the anteroposterior axis. Most of them contained sensory, sympathetic and parasympathetic nerve fibers. To avoid injury to nerves during surgical treatment of rectocele, an approach along the immediately vaginal side of the longitudinal muscle coat seems to be suitable.