The colonic blood supply penetrates the muscular layers of the bowel wall to ramify in the submucosal layer. The points of penetration, on the lateral sides of the three taeneae, create weaknesses that allow mucosa and submucosa to protrude from intracolonic pressure. These pseudodiverticula are subject to inflammation, perforation, and bleeding from erosion of the adjacent vessel by a fecolith. Bleeding often takes the form of multiple self-limited episodes. Diverticulitis can be complicated by abscess, bleeding or obstruction. A contained abscess may secondarily rupture causing peritonitis. An abscess between sigmoid and bladder may decompress into the bladder leaving a colovesical fistula Diverticulitis is the most common cause of colovesicle fistula, followed by cancer and Crohnís.
The lateral reflection of peritoneum off the right and left colon represent the limit of fusion of the colonic mesentery with the posterior parietal peritoneum in embryologic life. Elevating the colon in preparation for mobilization accentuates this boundary by folding up the edge of peritoneum . By incising just inside this line (white line of Toldt) one recreates the primitive mesentery. When in the proper plane, a moist sponge-stick bluntly dissects the avascular areolar tissue off the mesentery, pushing the ureter down and out of harmís way.
The rectum is approximately 16 cm in length. The lowest 4 cm constitutes the anal canal surrounded by internal and external sphincters. Each additional 4-cm segment is marked by one of the three anal valves. The upper 1/3 (4 cm) of the rectum is above the peritoneal reflection. The rectovesicle recess (pouch of Douglas) is the most dependent spot in the pelvis and in the male abdomen.