Acute mesenteric ischemia is interruption of intestinal blood flow by embolism, thrombosis, or a low-flow state. It leads to mediator release, inflammation, and ultimately infarction. Abdominal pain is out of proportion to physical findings. Early diagnosis is difficult, but angiography and exploratory laparotomy have the most sensitivity; other imaging modalities often become positive only late in the disease. Treatment is by embolectomy, revascularization of viable segments, or resection; sometimes vasodilator therapy is successful. Mortality is high.

Pathophysiology

The intestinal mucosa has a high metabolic rate and, accordingly, a high blood flow requirement (normally receiving 20 to 25% of cardiac output), making it very sensitive to the effects of decreased perfusion. Ischemia disrupts the mucosal barrier, allowing release of bacteria, toxins, and vasoactive mediators, which in turn leads to myocardial depression, systemic inflammatory response syndrome (see Sepsis and Septic Shock), multisystem organ failure, and death. Mediator release may occur even before complete infarction. Necrosis can occur as soon as 10 to 12 h after the onset of symptoms.

Etiology

Three major vessels serve the abdominal contents: the celiac trunk, the superior mesenteric artery (SMA), and the inferior mesenteric artery (IMA). The celiac trunk supplies the esophagus, stomach, proximal duodenum, liver, gallbladder, pancreas, and spleen. The SMA supplies the distal duodenum, jejunum, ileum, and colon to the splenic flexure. The IMA supplies the descending colon and sigmoid colon and the rectum. Collateral vessels are abundant in the stomach, duodenum, and rectum; these areas rarely develop ischemia. The splenic flexure is a watershed between the SMA and IMA and is at particular risk of ischemia.

Mesenteric blood flow may be disrupted on either the venous or arterial sides. In general, patients > 50 are at greatest risk and have the types of occlusions and risk factors shown in Table 3: Acute Abdomen and Surgical Gastroenterology: Causes of Acute Mesenteric Ischemia. However, many patients have no identifiable risk factors.

Table 3
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Causes of Acute Mesenteric Ischemia Occlusion Type Risk Factors Arterial embolus (> 40%) Coronary artery disease, heart failure, valvular heart disease, atrial fibrillation, history of arterial emboli Arterial thrombosis (30%) Generalized atherosclerosis Venous thrombosis (15%) Hypercoagulable states, inflammatory conditions (eg, pancreatitis, diverticulitis), trauma, heart failure, renal failure, portal hypertension, decompression sickness Nonocclusive ischemia (15%) Low-flow states (eg, heart failure, shock, cardiopulmonary bypass), splanchnic vasoconstriction (eg, vasopressors, cocaine)

Symptoms and Signs

The early hallmark of mesenteric ischemia is severe pain but minimal physical findings. The abdomen remains soft, with little or no tenderness. Mild tachycardia may be present. Later, as necrosis develops, signs of peritonitis appear, with marked abdominal tenderness, guarding, rigidity, and no bowel sounds. The stool may be heme-positive (increasingly likely as ischemia progresses). The usual signs of shock develop and are frequently followed by death.

Sudden onset of pain suggests but is not diagnostic of an arterial embolism, whereas a more gradual onset is typical of venous thrombosis. Patients with a history of postprandial abdominal discomfort (which suggests intestinal angina) may have arterial thrombosis.

Diagnosis

• Clinical diagnosis more important than diagnostic tests
• Mesenteric angiography or CT angiography if diagnosis unclear

Early diagnosis is particularly important because mortality increases significantly once intestinal infarction has occurred. Mesenteric ischemia must be considered in any patient > 50 with known risk factors or predisposing conditions who develops sudden, severe abdominal pain.

Mesenteric Ischemia

Patients with clear peritoneal signs should proceed directly to the operating room for both diagnosis and treatment. For others, selective mesenteric angiography or CT angiography is the diagnostic procedure of choice. Other imaging studies and serum markers can show abnormalities but lack sensitivity and specificity early in the course of the disease when diagnosis is most critical. Plain abdominal x-rays are useful mainly in ruling out other causes of pain (eg, perforated viscus), although portal venous gas or pneumatosis intestinalis may be seen late in the disease. These findings also appear on CT, which may also directly visualize vascular occlusion—more accurately on the venous side. Doppler ultrasonography can sometimes identify arterial occlusion, but sensitivity is low. MRI is very accurate in proximal vascular occlusion, less so in distal vascular occlusion. Serum markers (eg, creatine kinase, lactate) rise with necrosis but are nonspecific findings that are seen later. Intestinal fatty acid binding protein in the serum may prove valuable in the future as an early marker.

Prognosis

If diagnosis and treatment take place before infarction occurs, mortality is low; after intestinal infarction, mortality approaches 70 to 90%. For this reason, clinical diagnosis of mesenteric ischemia should supersede diagnostic tests, which may delay treatment.

Treatment

• Surgical: Embolectomy, revascularization, with or without bowel resection
• Angiographic: Vasodilators or thrombolysis
• Long-term anticoagulation or antiplatelet therapy

If diagnosis is made during exploratory laparotomy, options are surgical embolectomy, revascularization, and resection. A “second look” laparotomy may be needed to reassess the viability of questionable areas of bowel. If diagnosis is made by angiography, infusion of the vasodilator papaverineSome Trade Names
PAVABID
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through the angiography catheter may improve survival in both occlusive and nonocclusive ischemia. PapaverineSome Trade Names
PAVABID
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is useful even when surgical intervention is planned and is sometimes given during and after surgical intervention as well. In addition, for arterial occlusion, thrombolysis or surgical embolectomy may be done. The development of peritoneal signs at any time during the evaluation suggests the need for immediate surgery. Mesenteric venous thrombosis without signs of peritonitis can be treated with papaverineSome Trade Names
PAVABID
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followed by anticoagulation with heparinSome Trade Names
HEPFLUSH-10
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and then warfarinSome Trade Names
COUMADIN
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.

Patients with arterial embolism or venous thrombosis require long-term anticoagulation with warfarinSome Trade Names
COUMADIN
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. Patients with nonocclusive ischemia may be treated with antiplatelet therapy.

Key Points

• Early diagnosis is critical because mortality increases significantly once intestinal infarction has occurred.
• Initially, pain is severe but physical findings are minimal.
• Surgical exploration is often the best diagnostic measure for patients with clear peritoneal findings.
• For other patients, mesenteric angiography or CT angiography is done.
• Treatment options include embolectomy, revascularization, and resection.

Last full review/revision August 2012 by Parswa Ansari, MD

Content last modified November 2012