Mesenteric ischemia
Mesenteric ischemia is inadequate blood flow to the intestines through the mesenteric vessels, causing abdominal pain and, if untreated, bowel infarction. It can be acute — a surgical emergency — or chronic, producing pain after meals.
Mesenteric ischemia occurs when blood flow through the mesenteric arteries is insufficient to meet the intestines' demands, injuring the bowel wall. The celiac trunk, superior mesenteric artery (SMA), and inferior mesenteric artery supply the gut; compromise of these vessels — especially the SMA — threatens the small intestine and proximal colon.
Acute mesenteric ischemia is the dangerous form. Causes include an embolus to the SMA (classically from atrial fibrillation), in-situ arterial thrombosis over atherosclerotic plaque, mesenteric venous thrombosis, and non-occlusive ischemia from low-flow states such as shock or heart failure. The classic presentation is severe abdominal pain out of proportion to the physical exam — the abdomen may be soft while the patient is in agony. Labs may show lactic acidosis and leukocytosis; CT angiography is the usual diagnostic study. Without prompt revascularization, the bowel infarcts, leading to perforation, peritonitis, and high mortality.
Chronic mesenteric ischemia, sometimes called intestinal angina, results from progressive atherosclerosis of multiple mesenteric vessels. Patients — typically older adults with vascular risk factors — develop postprandial abdominal pain beginning shortly after meals, food fear, and weight loss, because digestion raises intestinal oxygen demand that the narrowed vessels cannot meet. Ischemic colitis, by contrast, is a related condition affecting watershed areas of the colon, usually in low-flow states, and tends to present with crampy pain and bloody diarrhea.
USMLE Step 1 tests mesenteric ischemia in gastrointestinal pathology: recognize "pain out of proportion to exam" for acute disease, postprandial pain with weight loss for chronic disease, and the distinction from ischemic colitis at the splenic flexure watershed.
Key takeaways
- Mesenteric ischemia is inadequate intestinal blood flow, most often involving the superior mesenteric artery.
- Acute mesenteric ischemia classically causes severe pain out of proportion to the physical exam and is a surgical emergency.
- Common acute causes are SMA embolism (think atrial fibrillation), arterial thrombosis, venous thrombosis, and low-flow states.
- Chronic mesenteric ischemia causes postprandial pain, food aversion, and weight loss from mesenteric atherosclerosis.
- Distinguish it from ischemic colitis, which favors watershed regions of the colon and presents with bloody diarrhea.