Ischemic Syndromes

Ischemic syndromes occur more often in the colon than in the stomach or small intestine, because collateral circulation is not as well developed in the colon.

Colonic ischemia may result in gangrene of the colon--a fulminating, undiagnosable abdominal catastrophe--or a milder version called ischemic colitis--a nongangrenous, spontaneously resolving process that can result in a fibrous colonic stricture. In the stomach and small intestine, acute mesenteric ischemia from arterial occlusion results from a thrombosis or an embolus in the celiac axis or superior mesenteric artery and causes midgut necrosis. If not immediately diagnosed, midgut necrosis almost always causes death. Even with intervention, > 90% of patients die. Less commonly, chronic arterial occlusive disease and acute venous thrombosis can lead to ischemic syndromes. Pain out of proportion to the examination is a hallmark sign of intestinal ischemia; recognizing this pain is key to early diagnosis.

Colonic Ischemia

Colonic ischemia is common in persons in their 60s and 70s. It is often associated with cardiovascular disorders, including heart failure, myocardial infarction, and pulmonary embolism, and with severe hemorrhage and the postoperative state. Gangrene of the colon commonly occurs in elderly patients in intensive care units with heart failure and sepsis.

The gangrenous form more likely involves the entire colon, with the splenic flexure being most severely affected; in contrast, the milder ischemic (nongangrenous) form more likely involves only a segment of the colon.

Symptoms of a gangrenous colon are generalized abdominal pain (particularly in the left iliac fossa and left hypochondrium), nausea, vomiting, diarrhea, and occasionally frank rectal bleeding. The physical findings suggest an abdominal catastrophe with generalized peritonitis in a patient who is extremely ill. These findings include generalized abdominal tenderness, aperistalsis, and hypotension with cardiovascular collapse. The diagnosis is often confused with perforation of a hollow viscus, fulminant pancreatitis, or mesenteric ischemia. At surgery, the colon is edematous and discolored, with the worst changes at the splenic flexure. A subtotal colectomy is required.

Nongangrenous colitis produces milder symptoms and signs, and an exploratory laparotomy usually is not performed. Acute pain usually occurs in the left iliac fossa; fever and a moderate amount of dark rectal bleeding often occur. On examination, localized left-sided peritonitis suggestive of diverticulitis is found. However, these two conditions can be distinguished based on the degree and quality of the rectal bleeding. The rectal bleeding associated with ischemic colitis usually is bright red, whereas the rectal bleeding associated with diverticulitis is usually occult. Massive rectal bleeding usually occurs in patients with diverticulosis without clinical evidence of diverticulitis. If colonoscopy is performed on a patient with ischemic colitis, the mucosa appears bluish and edematous with mucosal ulcerations and contact bleeding. A barium enema may show thumbprinting, a series of blunt semiopaque projections into the lumen, representing edematous haustra. Treatment is with resuscitation and bowel rest until symptoms abate (usually a few days).

Acute Mesenteric Ischemia

This syndrome is characterized by a sudden onset of severe abdominal colic followed by rectal passage of mucus and blood and circulatory collapse within a few hours. One hallmark is that the severe pain at onset is well out of proportion to the physical findings. However, peritonitis follows promptly with dramatic physical findings and leads to circulatory shock. With the onset of peritonitis, the initial colic is replaced by generalized abdominal pain, ileus, and distention.

None of the simple diagnostic tools specifically identifies acute mesenteric ischemia. The plain abdominal x-ray shows a pattern of ileus with gas-filled loops of edematous small intestine. By the time the diagnostic finding of air in the mesenteric veins appears, irreversible changes have already taken place. Laboratory findings, except for nonspecific leukocytosis, are not helpful in making an early diagnosis. Laparotomy is necessary to make a diagnosis; laparoscopy is not recommended.

Without treatment, this abdominal catastrophe commonly leads to death within 48 hours. The key to a successful outcome is very early operative intervention before peritonitis and irreversible shock become established. Unfortunately, in most cases, the presentation is not characteristic, and the diagnosis is made very late.

The only definitive treatment is early surgery that reestablishes blood flow by removing the embolus or bypassing the thrombosis in the visceral vessel. The nonviable intestine is resected. A "second-look" laparotomy should be performed in 24 hours to reevaluate the viability of the remaining intestine. After extensive small-intestine resections, parenteral nutrition is necessary, especially in the elderly. Perioperative management is especially difficult and requires close attention to fluid balance, antibiotic therapy, anticoagulation, and, often, control of metabolic acidosis.

Other Ischemic Syndromes

Chronic arterial obstruction of the celiac axis or superior mesenteric artery can result in profound weight loss and pain, suggesting abdominal angina. The pain, which is midabdominal or epigastric, often is worse postprandially. These features make this condition indistinguishable from many other more common abdominal conditions (eg, peptic ulcer disease). An arteriogram is diagnostic. Treatment is with aspirin (or another antiplatelet agent). Surgery with vascular reconstruction is used in patients whose disease is segmental rather than diffuse. Endoluminal stents placed by invasive vascular radiologists may also be used.

Acute mesenteric venous thrombosis usually results in death because it is not recognized until the majority of the bowel is infarcted. This disorder should be included in the differential diagnosis of an elderly patient with abdominal distention and pain disproportionate to the examination findings. CT with IV contrast often reveals superior mesenteric vein thrombus. Angiography should follow, with both catheter-based lytic therapy of the superior mesenteric vein and a lytic agent selectively introduced into the superior mesenteric artery. After thrombolysis, the patient must be maintained on an anticoagulant, and a hypercoagulation assessment must be performed. Occasionally, when the diagnosis is made late, a near-total resection of the small intestine allows survival, but it is a particularly devastating procedure in the elderly.