Pathophysiology
Clinical meaning
Acute mesenteric ischemia (AMI) is a vascular emergency resulting from insufficient blood flow to the intestines, causing rapid progression from mucosal injury to transmural necrosis, perforation, and death if not recognized and treated promptly. Mortality rates remain 60-80% due to delayed diagnosis. The intestinal blood supply comes from three major mesenteric arteries: the celiac artery (foregut โ stomach to proximal duodenum, liver, spleen, pancreas), the superior mesenteric artery (SMA, midgut โ distal duodenum to proximal two-thirds of transverse colon), and the inferior mesenteric artery (IMA, hindgut โ distal transverse colon to proximal rectum). The SMA supplies the largest territory and is the vessel most commonly involved in acute mesenteric ischemia. Four etiologic categories: (1) SMA embolism (40-50% of cases) โ most commonly from left atrial thrombus in atrial fibrillation, left ventricular thrombus post-MI, or valvular vegetations; emboli typically lodge 3-10 cm distal to the SMA origin (beyond the middle colic artery), sparing the proximal jejunum. (2) SMA thrombosis (20-30%) โ occurs at sites of pre-existing atherosclerotic stenosis, usually at the SMA ostium; patients often have a history of chronic mesenteric...