The two lateral dissections in the TME are time-consuming, as the surgeon carefully proceeds to expose the parietal fascia over the lateral pelvic wall structures. The fiberoptic lighted deep pelvic retractors are essential for clear visualization during lateral retraction of the rectum and anterior elevation of the bladder or the uterus and vagina. Better lighting may also be obtained with the use of a headlamp. The preservation of the pelvic autonomic nerve plexus and the anterior roots of sacral nerves S2, S3, and S4 is essential for anal continence and sexual function. The plexus is seen as a dense plaque of nerve tissue that comes close to the rectum at the level of the prostate or upper vagina. The TME does not encounter “lateral suspensory ligaments” but rather a fusion of the lateral mesorectum with tissue that may contain the middle hemorrhoidal arteries as the dissection heads toward the autonomic nerve plexus. This tissue is divided with electrocautery, and the middle hemorrhoidal vessels may require a ligature. The course of the ureters and the autonomic plexus is noted as the dissection is carried down to the levators (Figure 10).
After the rectum is transected, the specimen should have a wide zone of relatively smooth fat about the middle and upper rectum. In a thin patient, the pelvic nerves and autonomic nerve plexuses may just be visible beneath the parietal fascia, whereas the prostate and seminal vesicles are uncovered.
After it has been determined that the rectal tumor can be completely freed from the adjacent structures, the blood supply to the rectosigmoid is divided. The venous drainage should be ligated as early as possible to keep the vascular spread of tumor cells to a minimum. Although involved lymph nodes may not be evident in the mesentery over the bifurcation of the aorta, it is desirable to ligate the inferior mesenteric artery just distal to the origin of the left colic artery (Figure 11). The contents of the proximal clamps are tied, and the ligation is reinforced by a transfixing suture. Some prefer to ligate the inferior mesenteric artery as near its point of origin from the aorta as possible. Usually, this level is surprisingly near the ligament of Treitz. The blood supply to the sigmoid to be used as a colostomy is now derived from the middle artery through the marginal artery of Drummond.