Several important anatomic facts influence the technique of surgery in the large intestine. As a consequence of its embryologic development, the colon has two main sources of blood supply. The cecum, ascending colon, and proximal portion of the transverse colon are supplied with blood from the superior mesenteric artery, whereas the distal transverse colon, splenic flexure, descending colon, sigmoid, and upper rectum are supplied by branches of the inferior mesenteric artery (see Chapter 9 for identification of the blood supply).
Advantage may be taken of the free anastomotic blood supply along the medial border of the bowel by dividing either the inferior mesenteric artery or the middle colic artery and by depending on the collateral circulation through the marginal artery of Drummond to maintain the viability of a long segment of intestine. The peritoneal reflection on the lateral aspect of the colon is practically bloodless, except at the flexures or in the presence of ulcerative colitis or portal hypertension, and the peritoneum may be completely incised without causing bleeding or jeopardizing the viability of the bowel. When the lateral peritoneum is divided and the greater omentum freed from the transverse colon, extensive mobilization is possible, including derotation of the cecum into the right or left upper quadrant. Care should be taken to avoid undue traction on the splenic flexure lest attachments to the capsule of the spleen be torn and troublesome bleeding occurs. In the presence of malignancy of the transverse colon, the omentum is usually resected adjacent to the blood supply of the greater curvature of the stomach.
After the colon has been freed from its attachments to the peritoneum of the abdominal wall, the flexures, and the greater omentum, it can be drawn toward the midline through the surgical incision limited only by the length of its mesentery. This mobility of the colon renders the blood supply more accessible and often permits a procedure to be performed outside the peritoneal cavity. The most mobile part of the large bowel is the sigmoid because it normally possesses a long mesentery, whereas the descending colon and right half of the colon are fixed to the lateral abdominal wall.
The lymphatic distribution of the large bowel conforms to the vascular supply. Knowledge of this is of great surgical importance, especially in the treatment of malignant neoplasm, because an adequate extirpation of potentially involved lymph nodes requires the sacrifice of a much larger portion of the blood supply than would at first seem essential. The lymphatic spread of carcinoma of the large intestine along the major vascular supply has been responsible for the development of classic resections. However, a local sleeve resection for malignancy may be indicated in the presence of metastasis or because of the patient's poor general condition. When a curative resection is planned, the tumor and adjacent bowel must be sufficiently mobilized to permit removal of the immediate lymphatic drainage area.