The dissection commences as the first assistant, either from the left side of the abdomen or alternatively from between the legs, exposes the IMA for the surgeon. This is done by retracting the mesosigmoid in a ventro-lateral direction using bowel graspers from the left upper and lower quadrants. The surgeon incises the peritoneum to the right of the superior rectal artery starting at the sacral promontory (Figure 8.6.3). Under continuous traction, the peritoneum is incised cephalad toward the origin of the IMA. Using a combination of gentle spreading and electrosurgical dissection, the IMA is swept ventrally and the preaortic hypogastric neural plexus is swept dorsally to prevent injury. Small visceral branches of the nerves, supplying the colon and upper rectum, may be safely divided, while carefully preserving the main trunks leading into the pelvis, then the IMA is divided using a LigaSure device or endoscopic stapler (Figure 8.6.4).
Dissection then is continued medially beneath the artery, and the left ureter and gonadal vessels are identified and swept posteriorly (Figure 8.6.5). Tension is placed on the left colon and its mesenteric attachments by applying medial and cephalad traction with graspers, which should not be used to directly grasp the intestine, thus minimizing the chance of inadvertent visceral injury. If the left ureter cannot be identified easily from the medial approach, the lateral attachments of the sigmoid colon are incised, the sigmoid colon is mobilized left to right, and the gonadal vessels and ureter are identified and freed from the mesentery. It is helpful in this instance to place a cotton gauze sponge on top of these retroperitoneal structures (between them and the posterior aspect of the
sigmoid colon mesentery), thus when the surgical team goes back to the medial aspect of the IMA, the gauze immediately separates the ureter and gonadal vessels from the mesentery about to be divided (Figure 8.6.6 with inset).
With the IMA identified and ligated, the peritoneum is incised anteriorly over the pedicle, dissecting leftward toward the inferior mesenteric vein (IMV). Careful dissection with a right-angled dissector is used to create a peritoneal window just lateral to the IMA and IMV. This pedicle is ligated above or below the left colic artery (according to the surgeon's judgment) using a LigaSure device, but only if the left ureter can be clearly identified and retracted to avoid injury (Figure 8.6.7). We prefer to leave the IMA and IMV 1.0-1.5 cm long so that if any bleeding occurs, an additional grasping of the vessel is possible with application of another seal of the LigaSure device (or alternatively looping by an endoscopic loop can be done).
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