SMA Embolus vs Thrombosis
SMA embolus: Filling defect typically 3–10 cm from SMA origin (beyond origin at middle colic artery), often cardiac source (Afib, endocarditis); spares proximal jejunum.
SMA thrombosis: Occlusion at or near SMA origin, atherosclerotic disease, ischemia of entire SMA territory including proximal jejunum; longer segment ischemia; prior intestinal angina history.
Etiology and CT Findings
| Etiology | CT Findings | Territory |
|---|---|---|
| SMA occlusion — embolus | Filling defect in SMA 3–10 cm from origin; bowel wall thickening → thinning (necrosis); pneumatosis; portal venous gas; lack of bowel wall enhancement; mesenteric stranding | Mid-jejunum to transverse colon; spares proximal jejunum and duodenum (SMA branches beyond origin occluded) |
| SMA occlusion — thrombosis | Atherosclerotic calcification/plaque at SMA origin; near-complete or complete occlusion at origin; extensive small bowel and right colon ischemia; collateral vessels may be visible | Entire SMA territory including proximal jejunum; duodenum may be involved; longer ischemic segment than embolus |
| SMV thrombosis | Hyperdense SMV (acute thrombus); filling defect in SMV ± portal vein; mesenteric edema and ascites (venous congestion); bowel wall thickening (target sign/halo); hemorrhagic infarction more common than arterial; pneumatosis less common early | Variable; often patchy; mesenteric venous distribution; may spare arterially supplied areas; hypercoagulable states, portal hypertension, pancreatitis |
| Non-occlusive mesenteric ischemia (NOMI) | Patent mesenteric vessels; diffuse bowel wall thickening; poor bowel wall enhancement; mesenteric edema; no filling defect; SMA vasospasm may be visible on angiography | Watershed areas most vulnerable: splenic flexure, sigmoid; diffuse distribution possible; ICU/low-flow states, dialysis, vasopressors |
| Colonic ischemia (watershed) | Bowel wall thickening ± thumbprinting (submucosal edema); pericolonic stranding; watershed zones; typically no occlusion on CT; pneumatosis in severe cases | Splenic flexure (Griffiths point) and rectosigmoid junction (Sudeck point) — watershed zones between SMA/IMA and IMA/internal iliac territories |
| Strangulation / closed-loop | Closed loop morphology + wall thickening + loss of enhancement + mesenteric engorgement + ascites + pneumatosis; combination of arterial and venous compromise due to twisting | Isolated closed loop; variable size; sigmoid or internal hernia most common; rapidly progressive to full-thickness necrosis |
Critical finding: Pneumatosis intestinalis (intramural gas) + portal venous gas = grave prognosis — indicates advanced bowel necrosis with transmural infarction. Report immediately and obtain urgent surgical consultation. Distinguish pneumatosis from intraluminal gas: pneumatosis follows bowel wall contour, seen on multiple planes, often linear or bubbly in pattern.
References
Menke J. Diagnostic accuracy of MDCT for acute mesenteric ischemia: A systematic review. Eur Radiol. 2010;20(12):2805–14.
Radiopaedia — Bowel ischaemia