Colonic Diverticulosis and Diverticular Hemorrhage

Colonic diverticulosis predisposes individuals to lower gastrointestinal hemorrhage in up to 5% of cases. These sac-like protrusions are pseudodiverticula and arise due to a combination of anatomic, dietary, motility, and structural influences. In the setting of acute hemorrhage, patient stabilization takes priority, followed closely by maneuvers aimed at localizing and controlling blood loss. Through the use of an arsenal of tools including colonoscopy, angiography, and nuclear scintigraphy, most diverticular bleeds can be localized and subsequently controlled. When persistent and not controlled by colonoscopic or angiographic means, expeditious surgical resection serves as definitive therapy. PATHOGENESIS OF DIVERTICULAR BLEEDING The various colonic arterioles penetrate the muscular wall en route to the colonic mucosa. Sometime these arterioles can divide, with one branch penetrating the wall at the site of a diverticulum and the other branch passing external to the muscular layer and being displaced over the dome of the diverticulum. It appears likely that luminal traumatic factors, including chronic injury and impacted fecaliths which cause abrasion of the vessels, lead to the formation of ulcerations and erosions that ultimately result in hemorrhage. Structural changes occur in the wall of the affected vessel, with thickening of the intima and focal attenuation of the media. The anatomic basis for bleeding is thought to be asymmetric rupture of these intramural branches (the vasa recta) of the marginal artery at either the dome of the diverticulum or at its antimesenteric margin. Vessel disruption occurs on the mucosal side of the artery, as bleeding occurs into the lumen instead of into the peritoneal cavity. Inflammation is no longer the presumed underlying cause of diverticular bleeding as little or no inflammation is found in resected specimens and hemorrhage is rarely seen in the setting of acute diverticulitis. Diverticular hemorrhage is thought to occur in 3 to 5% of all patients with colonic diverticulosis, yet appears to cease spontaneously in up to 90% of patients. Transfusion of greater than four units of packed red blood cells is rare, with some data suggesting that when hemorrhage is limited to less than four units/day, bleeding stops in up to 99% of cases. After an initial episode of hemorrhage, rebleeding is likely to occur in 10% of patients in the first year; thereafter, the risk for rebleeding increases to 25% at 4 years. Emergency surgical intervention for ongoing massive hemorrhage is rarely necessary before attempts are made to localize the precise source of bleeding. This allows an orderly approach to identification of the bleeding site, which is essential for appropriate therapy. After the initial patient resuscitation and concurrent to the ongoing stabilization, diagnostic testing should begin. The choice of initial investigation remains controversial and depends on local availability of resources and expertise. "