Pathogenesis of massively bleeding colonic diverticulosis: new observations.

Colonic diverticulosis is a common cause of acute severe rectal hemorrhage. The precise site of bleeding, etiology, and pathogenesis have not been previously identified. Arteriographic, microangiographic, and detailed histologic observations in 10 cases of massively bleeding colonic diverticulosis demonstrated strikingly consistent changes related to the characteristic angioarchitecture of colonic diverticula. These changes included: (1) asymmetric rupture of the vas rectum toward the lumen of the diverticulum precisely at its dome or its antimesenteric margin; (2) conspicuous eccentric intimal thickening of the vas rectum, often with thinning of the media and duplication of the internal elastic lamina at and near the bleeding point; and (3) general absence of diverticulitis. Comparison with control colonic diverticula suggests that traumatic factors arising within the diverticular or colonic lumen induce asymmetric intimal proliferation and segmental weakening of the associated vas rectum, predisposing to rupture and massive bleeding.