The thickened and vascular greater omentum is retracted upward in preparation for its separation from the transverse colon. An incision is made in the omental reflection along the superior surface of the colon (Figure 5). Since the omentum may be quite adherent to the colon, it may be easier to divide the gastrocolic omentum nearer the stomach than the transverse colon. This can be facilitated if the surgeon places his or her left hand, palm upward, in the lesser sac in order to better define the gastrocolic omentum. Most of the dissection can be done with electrocautery, especially if the relatively avascular plane is present where the omentum joins the transverse colon. If large vessels are encountered, paired curved clamps are applied and their contents ligated.
Special attention is required during the division of the thickened splenocolic ligament to avoid tearing the splenic capsule by undue tension (Figure 6). The splenocolic ligament is divided at some distance, if possible, from the inferior pole of the spleen (Figure 7). When the splenic flexure and descending colon have been partially freed down to the region of the sigmoid, the surgeon may wish to return to the region of the right colon and control the blood supply to the bowel before removing it in order to facilitate the eventual exposure of the pelvis for the exploration of the rectum. The mobilized right colon is drawn outside the peritoneal cavity, and the vessels in the mesentery can be identified easily (Figure 8). Enlarged lymph nodes often fill in the arcades about the mesenteric border. Unless malignancy has been found, the blood supply can be ligated near the bowel wall as shown in Figure 8. Before the blood supply is ligated, the ureter is protected posteriorly by warm, moist packs.