Deep Pelvic Anatomy Revisited for a Description of Crucial Steps in Extralevator Abdominoperineal Excision for Rectal Cancer

Abstract

Extralevator abdominoperineal excision results in superior oncologic outcome for advanced low rectal cancer. The exact definition of surgical resection planes is pivotal to achieving negative circumferential resection margins. This study aims to describe the surrounding anatomical structures that are at risk for inadvertent damage during extralevator abdominoperineal excision. Joint surgical and macroanatomical dissection was performed in a university laboratory of clinical anatomy. A stepwise dissection study was conducted according to the technique of extralevator abdominoperineal excision by abdominal and perineal approaches in 4 human cadaveric pelvises. Muscular, fascial, tendinous, and neural structures were carefully exposed and related to the corresponding surgical resection planes. In addition to the autonomic nerves to be identified and preserved during total mesorectal excision, further structures endangered during extralevator abdominoperineal excision can be clearly identified. Terminal pudendal nerve branches come close to the surgical resection plane at the outer surface of the puborectal sling. Likewise, the pelvic plexus and its neurovascular bundles embedded within the parietal pelvic fascia extend close to the apex of the prostate where the parietal pelvic fascia has to be divided. These neural structures converge in the region of the perineal body, an area that provides no "self-opening" planes for surgical dissection. Thus, the necessity to sharply detach the anorectal specimen anteriorly from the perineal body and the superficial transverse perineal muscle bears the risk of both inadvertent damage of the aforementioned anatomical structures and perforation of the specimen. The study focused primarily on the macroscopic topography relevant to the surgical procedure, so that previously published histologic examinations were not performed. The present anatomical dissection study highlights those anatomical landmarks that require clear identification for the successful achievement of both negative circumferential resection margins and preservation of urogenital functions during extralevator abdominoperineal excision.