Acute mesenteric ischaemia affects the small bowel; ischaemic colitis affects watershed colon
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Acute mesenteric ischaemia (small bowel, superior mesenteric artery)
- Embolic (about 50 per cent): sudden onset, often with atrial fibrillation
- Thrombotic: on pre-existing atherosclerosis, often with preceding abdominal angina
- Non-occlusive: low flow states, vasopressors, cardiac failure
- Venous thrombosis: in thrombophilia or portal hypertension
Presentation is severe pain out of proportion to signs, with a raised lactate late. Mortality is high because diagnosis is often delayed until infarction.
Chronic mesenteric ischaemia: postprandial pain, food fear and weight loss, requiring stenosis of at least two of the three mesenteric vessels.
Ischaemic colitis: affects the watershed areas at the splenic flexure (Griffiths' point) and rectosigmoid (Sudeck’s point). Usually a low flow event in an older patient, presenting with left-sided pain and bloody diarrhoea, and generally with a far better prognosis than small bowel ischaemia.
The rectum is usually spared because of its dual supply from the internal iliac arteries, which is a useful diagnostic feature.