ESSENTIALS OF DIAGNOSIS
Severe postprandial abdominal pain.
Weight loss with a “fear of eating.”
Acute mesenteric ischemia: severe abdominal pain yet minimal findings on physical examination.
Acute mesenteric ischemia results from occlusive mesenteric arterial disease, either embolic occlusion or primary thrombosis of at least one major mesenteric artery. Ischemia can also result from nonocclusive mesenteric ischemia, which is generally seen in patients with low flow states, such as severe heart failure, sepsis, or hypotension. Chronic mesenteric ischemia, also called intestinal angina, occurs when increased flow demands during feeding are not met resulting in abdominal pain. Because of the rich collateral mesenteric network, generally at least two of the three major visceral vessels (celiac, superior mesenteric, inferior mesenteric arteries) must be 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.
1. Acute mesenteric ischemia
Visceral arterial embolism presents acutely with severe abdominal pain. In contrast, patients with primary visceral arterial thrombosis often have an antecedent history consistent with chronic mesenteric ischemia. The key finding with acute mesenteric ischemia is severe, steady, diffuse abdominal pain with an absence of focal tenderness or distention. This “pain out of proportion” to physical examination findings occurs because ischemia initially is mucosal and does not impact the peritoneum until transmural ischemia inflames the peritoneal lining. A high WBC count, lactic acidosis, hypotension, and abdominal distention may aid in the diagnosis.
2. Chronic mesenteric ischemia
Patients are generally over 45 years of age and may have evidence of atherosclerosis in other vasculature. 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. In severe cases of intestinal angina, patients may become dehydrated, which can cause hypotension and an acute thrombosis.
Characteristic symptoms are left lower quadrant pain and tenderness, abdominal cramping, and mild diarrhea (non-bloody or bloody). Rectal discharge will appear mucus-like or bloody and should prompt further evaluation.
B. Imaging and Colonoscopy
Contrast-enhanced CT is accurate at determining the presence of ischemic intestine. In acute or chronic mesenteric ischemia, a CTA or MRA can demonstrate narrowing of the proximal visceral vessels. In acute mesenteric ischemia from a nonocclusive low flow state, angiography is needed to display the typical “pruned tree” appearance of the distal visceral vascular bed (eFigure 12–8). Ultrasound scanning of the mesenteric vessels may show proximal obstructing lesions.