Ischemic bowel disease is caused by a compromise in the blood supply of the gut. Ischemic colitis is a relatively mild form of the condition, in which the disruption of blood flow is transient, necrosis is limited, and patients often recover in a couple of days with supportive care. Acute mesenteric ischemia can be due to either arterial or venous thrombosis and is a more serious ailment, with a relatively high rate of mortality.
Ischemic colitis is the most frequent manifestation of ischemic bowel disease. It is caused by a temporary reduction in the blood flow in small blood vessels. The symptoms are relatively mild, necrosis is restricted and rarely affects the full thickness of the gut; however, about 15% of cases will develop transmural necrosis and, as a result, peritonitis . On the other hand, acute mesenteric ischemia presents with severe pain and is often due to thrombosis or embolism. It may proceed to a compromise in the barrier function of the gut wall, leading to leakage into the peritoneum and systemic inflammation. Both ischemic colitis and mesenteric ischemia may be associated with a range of severity.
Ischemic bowel disease mainly affects the elderly. It may be induced by a variety of conditions, treatments, or medications. Physical exertion may lead to ischemia in the intestines. The ailment can follow vascular surgeries, such as aortic or cardiac bypass, and may be caused by inadequate perfusion during surgery or by ligation of the inferior mesenteric artery . Colonic ischemia is observed relatively frequently in abdominal aortic aneurysm (AAA) repair surgeries  and has been reported after placing a stent for AAA . Ischemic colitis can be a consequence of carcinoma or diverticulitis. Deficiencies of coagulation inhibitors (for example protein C) and other hypercoagulation disorders (factor V mutations, the antiphospholipid syndrome) occur in a high proportion of patients with colon ischemia . A large number of medications (for example antihypertensive drugs) may result in or contribute to ischemic colitis. Both arterial and venous thrombosis can be the main pathology responsible for acute mesenteric ischemia.
The initial symptoms of ischemic colitis are abdominal cramps (mainly on the left side), and an urge to defecate, followed by bloody stools - although there is no significant loss of blood. With care including bowel rest and fluid replacement, most patients recover within a couple of days. Surgery may be necessary in the presence of more advanced necrosis or if strictures develop. Severe necrosis will lead to the appearance of signs of peritonitis. Nausea, vomiting and some other findings indicate the development of ileus. Mesenteric ischemia begins with serious abdominal discomfort in the absence of any striking abnormality during a physical exam. Later in the course of the disease, features of peritonitis develop.
Laboratory tests show signs of ischemia, such as elevated lactic acid levels and acidosis, but these may develop too late for diagnosis.
Among the imaging techniques, plain abdominal radiography is not sensitive enough to detect ischemic colitis but may indicate towards mucosal edema (thumbprinting), and intramural gas, as well as intraperitoneal gas if there is a perforation. It is also useful for ruling out other conditions. Barium enema also detects thumbprinting in the large majority of patients with ischemic colitis , but the technique is not widely used anymore. The techniques of choice are colonoscopy and computed tomography (CT). In the early stages, colonic edema with pale mucous membranes, and capillary hemorrhages are found by colonoscopy. In later stages, a single linear ulcer may be detected . In severe cases, the membranes look blue, gray or black. CT will show, among other features, symmetrical thickening of the wall, uneven narrowing of the lumen, and edema. A segmental distribution of anomalies is also characteristic of ischemic colitis , and is one of the features that tend to occur less in inflammatory bowel disease; thus it may be used to distinguish the two conditions. Ultrasound is not widely used but may indicate luminal thickening, edema, hemorrhage, and intramural gas .
Timely identification is crucial in the case of acute mesenteric ischemia because of the high mortality rates. Angiography is useful, but the clinical assessment is of primary importance.