A well-vascularized segment of colon which can reach the rectum or the anus without tension is essential for a healthy anastomosis following total mesorectal excision. Achievement of this typically begins with complete mobilization of the sigmoid and descending colon, and often, the splenic flexure.[1] The sigmoid colon, descending colon, and their mesentery are mobilized to the midline such that, left gonadal vessels and ureter are easily visible within the retroperitoneum. Complete mobilization of the splenic flexure (as described in previous section) can be confirmed by seeing that the mesentery of left transverse and left colon are free from the pancreas, spleen, and left kidney such that those organs are easily visible. The transverse mesocolon can be mobilized up to the middle colic vessels.

In addition to complete mobilization, high ligation of the IMA and IMV, preserving the bifurcation of the left colic artery, allows additional length for a low colorectal or coloanal anastomosis (Figure 5.1).[1] For most patients, high ligation of the IMV alongside the ligament of Treitz is the maneuver that allows for the greatest lengthening of the descending colon mesentery for a low rectal anastomosis. In addition, adhesions between the proximal jejunum and transverse mesocolon can limit reach. Taking these down and incising the window of avascular mesentery bordered by the left ascending vessels, marginal artery, and IMV can gain length. Commonly, the greater omentum can wrap from the transverse colon to the descending colon and shorten this area. Taking down these adhesions will further straighten the colon.

In some individuals, tension is created as the mesocolon is brought lateral to the fourth portion of the duodenum, especially if the middle colic vessels have been taken and bowel has been transected such that that blood supply is reliant on the right or ileocolic vessels. This problem can be overcome by passing the mobilized bowel though a window in the midgut mesentery that is created by incising a window of avascular mesentery located between the superior mesenteric and ileocolic vessels.[2] The retroperitoneal attachments of the terminal ileum are incised, and the mobilized bowel is passed through the mesenteric window, behind the mesentery of the terminal ileum, and into the pelvis. Another option, initially described as the Deloyer’s procedure,[3] is complete mobilization of the cecum, right colon and hepatic flexure to allow for counter-clockwise rotation of the colon and passage of the large bowel down the right side of the abdomen into the pelvis. It is important to note that this maneuver will displace the position of the appendix, so appendectomy should be considered to avoid a misdiagnosis at a later date.[4]