Mesorectal excision: Surgical anatomy of the rectum, mesorectum, and pelvic fascia and nerves and clinical relevance

Abstract

Biologic behavior and management of rectal cancer differ significantly from that of colon cancer. The surgical treatment is challenging since the rectum has dual arterial blood supply and venous drainage, extensive lymphatic drainage and is located in a bony pelvic in close proximity to urogenital and neurovascular structures that are invested with intricate fascial covering. The rectum is encased by fatty lymphovascular tissue (mesorectum) that is surrounded by perirectal fascia that act as barrier to the spread of the cancer and constitute the surgical circumferential margin. Locoregional recurrence after rectal cancer surgery is influenced by tumor-related factors and adequacy of the resection. Local recurrence is associated with incomplete excision of circumferential margin, violation of perirectal fascia, transmesorectal dissection, presence of isolated deposits in the mesorectum and tumor in regional lymph nodes and incomplete lymph node clearance. Hence to eradicate the primary rectal tumor and control regional disease, the rectum, first area of lymph node drainage and surrounding tissue must be completely excised while maintaining an intact fascial envelope around the rectum and preserving surrounding structures. This is achieved with extrafascial dissection and removal of the entire mesorectum including the portion distal to the tumor (total mesorectal excision) within its enveloping fascia as an intact unit. Total mesorectal excision is the standard of care surgical treatment of mid and low rectal cancer and can be performed in conjunction with low anterior resection, abdominoperineal resection, extralevator abdominoperineal resection, and extraregional dissection. To accomplish such a resection, thorough knowledge of the surgical anatomy of the rectum and pelvic structures and fascial planes is paramount.

Keywords: Mesorectum, Pelvic fascia, Mesorectal excision

Core tip: Radical resection of rectal cancer entails removal of the rectum with its fascia as an intact unit while preserving surrounding vital structures. The procedure is technically challenging because of the complex multilayered pelvic fascia and intimate relationship between the rectum and vital surrounding structures. Despite the clear-cut “text book” description of surgical technique and straightforward manner of handling different structures in the pelvis, there are many variations and contradictory accounts reported in the literature as to the nature, anatomy and significance of some of the structures, proper plane of dissection, and the optimal technique to achieve oncological resection while decreasing urogenital and bowel dysfunction.