ISCHEMIC COLITIS
In older patients inflammatory bowel disease may be simulated by ischemic injury to the colon. This ischemic injury, which may be acute or chronic, usually occurs as a complication of severe atherosclerosis. More rarely it results from vascular injury secondary to surgery or a dissecting aneurysm, from a low cardiac output state, from vasculitis, or from a hypercoagulable state. The ischemia is more likely to occur in “watershed areas” between the distributions of two major vessels (splenic flexure, rectosigmoid area] and is usually secondary to hypoperfusion rather than to complete obstruction. The rectum is almost always spared because of its collateral blood supplies. The clinical picture may be acute or chronic, with all gradations between.
Acute ischemic colitis is usually manifested by the sudden onset of localized abdominal pain, tenderness, and rectal bleeding, which is sometimes associated with fever, hypotension, tachycardia, and peritoneal signs. Sigmoidoscopy or colonoscopy may show no abnormalities but more frequently shows multiple ulcers or bulging areas of submucosal hemorrhage. Barium enema examination is hazardous during the acute phase, but when carried out later most characteristically shows areas of narrowing and the changes in the bowel outline called “thumbprinting” caused by mucosal hemorrhage and edema. Acute ischemic colitis may be difficult to distinguish from IBD or diverticulitis. Most acute ischemic episodes resolve over the subsequent several weeks with general supportive measures. Angiography is rarely indicated, and surgery is reserved for patients with clear evidence of perforation and/or infarction. The patient who recovers from an acute episode may remain well subsequently or may enter a more chronic phase of the illness.