VISCERAL ARTERY INSUFFICIENCY (Intestinal Angina)
Acute visceral artery insufficiency results from either embolic occlusion or primary thrombosis of at least one major mesenteric vessel. Ischemia can also result from nonocclusive mesenteric vascular insufficiency, which is generally seen in patients with low flow states, such as heart failure, or hypotension.
A chronic syndrome occurs when there is adequate perfusion for the viscera at rest but ischemia occurs with severe abdominal pain when flow demands increase with feeding. Because of the rich collateral network in the mesentery, generally at least two of the three major visceral vessels (celiac, superior mesenteric, inferior mesenteric arteries) are affected before symptoms develop.
Ischemic colitis, a variant of mesenteric ischemia, usually occurs in the distribution of the inferior mesenteric artery. The intestinal mucosa is the most sensitive to ischemia and will slough if underperfused. The clinical presentation is similar to inflammatory bowel disease. Ischemic colitis can occur after aortic surgery, particularly aortic aneurysm resection or aortofemoral bypass for occlusive disease, when there is a sudden reduction in blood flow to the inferior mesenteric artery.
Symptoms and Signs
Acute intestinal ischemia: Patients with primary visceral arterial thrombosis often give an antecedent history consistent with chronic intestinal ischemia. The key finding with acute intestinal ischemia is severe, steady epigastric and periumbilical pain with minimal or no findings on physical examination of the abdomen because the visceral peritoneum is severely ischemic or infarcted and the parietal peritoneum is not involved. A high white cell count, lactic acidosis, hypotension, and abdominal distention may aid in the diagnosis.
Chronic intestinal ischemia: Patients are generally over 45 years of age and may have evidence of atherosclerosis in other vascular beds. Symptoms consist of epigastric or periumbilical postprandial pain lasting 1–3 hours. To avoid the pain, patients limit food intake and may develop a fear of eating. Weight loss is universal.
Ischemic colitis: Characteristic symptoms are left lower quadrant pain and tenderness, abdominal cramping, and mild diarrhea, which is often bloody.
A high suspicion of acute intestinal ischemia dictates immediate exploration to determine bowel viability. If the bowel remains viable, bypass using a prosthetic conduit can be done either from the supra-celiac aorta or common iliac artery to the celiac and the superior mesentery artery. In cases where bowel viability is questionable or bowel resection will be required, the bypass can be done with autologous vein to avoid the use of prosthetic conduits in a potentially contaminated field. Angioplasty and stenting of the arteries can be used but does not avoid a surgical evaluation of bowel viability.
In chronic intestinal ischemia, angioplasty and stenting of the proximal vessel may be beneficial depending on the anatomy of the stenosis. Should an endovascular solution not be available, an aorto-visceral artery bypass is the preferred management. The long-term results are highly durable. Visceral artery endarterectomy is reserved for cases with multiple lesions where bypass would be difficult.
The mainstay of treatment of ischemic colitis is maintenance of blood pressure and perfusion until collateral circulation becomes well established. The patient must be monitored closely for evidence of perforation, which will require resection.