Ischemic colitis is caused by mesenteric vascular occlusion or nonocclusive mechanisms. A common precipitating event is abdominal aortic reconstruction with interruption of a vital blood supply such as the inferior mesenteric artery. An entity that resembles ischemic colitis sometimes develops proximal to obstructing colonic carcinoma. Isolated ischemia of the right colon is seen in patients with chronic heart disease, especially aortic stenosis. Ischemic colitis most often afflicts the elderly (average age, 60 years), but it also occurs in younger adults in association with diabetes mellitus, systemic lupus erythematosus, or sickle cell crisis. Pancreatitis can occlude mesocolic vessels.
The most common location is the sigmoid colon (40%) followed by the transverse colon (17%), splenic flexure (11%), ascending colon (12%) and the rectum (6%). Ischemic colitis is categorized as reversible or irreversible. Reversible ischemia heals with nonoperative treatment, sometimes with stricture formation. Over half of the patients have a reversible injury. The severe form is fulminant from onset or may pursue an indolent course without resolution for weeks. Both of the severe forms require operation.
Symptoms of Ischemic colitis
Patients with ischemic colitis have an abrupt onset of abdominal pain, diarrhea (commonly bloody), and systemic symptoms. The abdomen may be tender diffusely, in a localized area (eg, left lower quadrant), or not at all. Blood is seen coming from above at endoscopy; the mucosa of the involved segment is edematous, hemorrhagic, friable, sometimes ulcerated. A grayish membrane may be present, resembling pseudomembranous colitis. Serum alkaline phosphatase is elevated in some cases. Plain abdominal x-rays are nonspecific. Barium enema x-rays show “thumbprints” or pseudotumors, typically limited to a 6- to 20-cm segment; 75% or more have involvement of the left colon. CT scan shows a thickened colonic wall and helps to exclude other conditions. Mesenteric arteriography may show major arterial occlusion or no abnormalities and is not usually recommended.
Differentiating ischemic colitis from carcinoma, ulcerative colitis, and diverticulitis should not be difficult, but Crohn’s disease presents a greater diagnostic problem. Rectal bleeding—especially gross hemorrhage—is less common in Crohn’s disease, the rapid onset of ischemic colitis is also different from Crohn’s disease. Radiographic findings and, in some cases, the colonoscopic appearance may be helpful, but the natural history of the acute attack is often the only way to make the distinction. Acute mesenteric ischemia may be difficult to exclude, but the more benign presentations of reversible ischemic colonic injury are not seen with ischemia of the small intestine. C difficile toxin is present in stool in pseudomembranous colitis.
Treatment of Ischemic colitis
Therapy for reversible ischemic colitis consists of intravenous fluids, antibiotics, and observation to be certain the problem is in fact reversible. Irreversible disease, whether fulminant from the beginning, becoming more severe over several days, or just failing to resolve after treatment, should be treated by operation. The diseased colon is resected; anastomosis is usually deferred if the colon is unprepared.