Superior mesenteric artery (SMA) aneurysm is focal or diffuse dilatation of the SMA exceeding 1.5 times the normal diameter (normal SMA diameter 6-8 mm). It constitutes 5-8% of visceral artery aneurysms (second or third most common after splenic artery aneurysms). Two main types: true aneurysm (involving all wall layers — atherosclerosis, FMD, medial degeneration) and pseudoaneurysm (full-thickness wall disruption, contained by adventitia or surrounding tissue — pancreatitis, trauma, infection). Pancreatitis-related pseudoaneurysms are the most common cause — pancreatic enzymes erode the wall of SMA branches. Rupture risk at 38-50% is higher than other visceral artery aneurysms, with rupture mortality of 30-50%. Most are asymptomatic and incidentally detected on CTA; symptomatic cases may present with abdominal pain, GI bleeding, and mesenteric ischemia. CTA is the gold standard; aneurysm diameter, morphology (saccular vs fusiform), thrombus presence, and associated pathology (pancreatitis) are assessed.
Age Range
35-75
Peak Age
55
Gender
Equal
Prevalence
Rare
SMA aneurysm develops through two different pathogeneses. In true aneurysms, the tunica media weakens from atherosclerosis (most common — 60%), fibromuscular dysplasia, medial degeneration, or vasculitis (PAN, Behçet) — elastin fragmentation and smooth muscle cell loss reduce wall tensile strength → the vessel segment progressively dilates under intraluminal pressure. Pseudoaneurysms result from full-thickness wall damage: in acute/chronic pancreatitis, pancreatic enzymes (trypsin, elastase, lipase) erode periarterial tissue and the wall of SMA branches → wall integrity is compromised → blood leaks into surrounding tissue and is contained by adventitia or organized hematoma forming a pseudoaneurysm. On CTA, true aneurysm has regular contour with dilatation involving all wall layers, while pseudoaneurysm has irregular contour, is eccentric, and surrounded by inflammatory changes (pancreatitis findings). True aneurysm lumen fills homogeneously with contrast while thrombus may partially fill the lumen. Pseudoaneurysm lumen fills with contrast but surrounding organized hematoma is seen. Rupture risk is high in both types — particularly high in pseudoaneurysms due to lack of structural wall support. Rupture may cause intraperitoneal hemorrhage (hemoperitoneum), bleeding into the GI lumen (hematemesis/melena), or retroperitoneal hematoma.
Focal saccular or fusiform dilatation of the SMA appears as a contrast-filled structure on CTA. True aneurysm has regular contour, symmetric; pseudoaneurysm has irregular contour, eccentric, surrounded by inflammatory changes (pancreatitis). Distinction determines treatment strategy.
Focal or diffuse dilatation exceeding 1.5 times normal diameter of the SMA on arterial phase CTA. Aneurysm fills with contrast showing high luminal density (200-400 HU). In true aneurysm, contour is regular and symmetric; in pseudoaneurysm, it is irregular, eccentric, with surrounding inflammatory changes. Aneurysm size, location (proximal SMA trunk vs branch), morphology (saccular/fusiform), and associated findings (thrombus, pancreatitis) should be reported in detail.
Report Sentence
__ mm diameter saccular/fusiform aneurysm of the SMA, consistent with __ (true aneurysm / pseudoaneurysm).
Pancreatitis-related inflammatory changes surrounding the SMA aneurysm/pseudoaneurysm on portal venous phase: peripancreatic fat stranding, pancreatic parenchymal heterogeneity, peripancreatic fluid collections, walled-off necrosis, or pseudocyst. These findings confirm pseudoaneurysm etiology and guide treatment planning. Pseudoaneurysm is usually localized in SMA branches near the pancreatic body/tail region.
Report Sentence
Peripancreatic inflammatory changes and fluid collection surrounding the SMA pseudoaneurysm, consistent with pancreatitis-related pseudoaneurysm.
Partial mural thrombus within the aneurysm lumen — density difference between enhancing patent lumen and non-enhancing thrombus is apparent. Thrombus carries risk of distal embolization potentially causing mesenteric ischemia/bowel infarction. Thrombus presence and extent affect treatment decisions — thrombus amount and patent lumen size are important for embolization planning.
Report Sentence
Partial mural thrombus in the SMA aneurysm lumen, should be evaluated for distal embolization risk.
Focal dilatation of the SMA and gadolinium enhancement in the aneurysm lumen on contrast-enhanced MRA. MRA is superior to CTA for characterizing pseudoaneurysm surrounding tissue — organized hematoma shows T1 hyperintensity (methemoglobin), mixed signal on T2. DWI is useful for evaluating surrounding tissue infection (abscess). TOF MRA shows the aneurysm patent lumen but contrast-enhanced MRA is preferred for thrombus-lumen differentiation.
Report Sentence
Focal dilatation of the SMA with enhancement in the aneurysm lumen on MRA, consistent with SMA aneurysm.
On Doppler US, focal dilatation of the SMA and turbulent flow pattern in the aneurysm lumen. On color Doppler, 'yin-yang' (to-and-fro) flow pattern may be seen in the pseudoaneurysm lumen — blood flowing in and out of the entry point is displayed with opposing color codes. Bidirectional flow is detected at the aneurysm neck level on spectral Doppler. US is useful for initial evaluation but sensitivity is limited due to the deep location of the SMA.
Report Sentence
Focal dilatation of the SMA with yin-yang flow pattern on Doppler, consistent with pseudoaneurysm; further evaluation with CTA recommended.
In ruptured SMA aneurysm, active contrast extravasation around the aneurysm or into the peritoneal/retroperitoneal space on arterial phase CTA. Hemoperitoneum or retroperitoneal hematoma accompanies. Pseudoaneurysm rupture into bowel lumen causes GI bleeding (hematemesis/melena) — contrast accumulation in the bowel lumen may be detected. Active extravasation is an indication for emergent intervention (embolization or surgery).
Report Sentence
Active contrast extravasation around the SMA aneurysm, consistent with rupture; emergent intervention (embolization/surgery) is indicated.
Criteria
Dilatation involving all wall layers. In setting of atherosclerosis, FMD, or medial degeneration. Regular contour, symmetric.
Distinct Features
Usually in proximal SMA trunk. Mural thrombus common. Calcified wall may be visible. Fusiform morphology more common.
Criteria
Full-thickness wall disruption, contained by surrounding tissue. Results from pancreatic enzyme erosion. Irregular contour, eccentric, pancreatitis findings.
Distinct Features
Most common etiology. Common in SMA branches (jejunal, ileal arteries). High rupture risk. May be localized within peripancreatic collection. Treatment: transarterial embolization first choice.
Criteria
Results from bacterial embolization (endocarditis) or perivascular infection. Saccular morphology, perianeurysmal inflammation, rapid growth.
Distinct Features
Fever and positive blood cultures accompany. Perianeurysmal soft tissue and gas may be present. Antibiotic treatment + surgery/embolization. Rapid growth indicates high rupture risk.
Distinguishing Feature
In PAN, multiple small microaneurysms (<10 mm) in multiple vascular beds (renal, hepatic, mesenteric) with beading pattern; isolated SMA aneurysm is usually single and larger.
Distinguishing Feature
Pseudocyst does not enhance (low density, 0-20 HU); pseudoaneurysm shows marked arterial enhancement (200-400 HU). This distinction is critical for treatment — pseudoaneurysm drainage may cause life-threatening hemorrhage.
Distinguishing Feature
SMA stenosis/thrombosis presents with mesenteric ischemia — filling defect in lumen and distal bowel wall enhancement loss; in aneurysm, dilatation predominates.
Distinguishing Feature
Splenic artery aneurysm in left upper quadrant near splenic hilum; SMA aneurysm in central abdomen along SMA course. Anatomic location is distinguishing.
Urgency
urgentManagement
interventionalBiopsy
Not NeededFollow-up
6-monthSMA aneurysm treatment is planned based on aneurysm type, size, and symptom presence. Pseudoaneurysms should be treated regardless of size because rupture risk is very high (38-50%). Transarterial embolization (coil or glue) is the first-line treatment — especially for pancreatitis-related pseudoaneurysms. For true aneurysms, treatment is indicated when diameter >20 mm or symptoms present. Surgical resection + revascularization needed when embolization is not feasible. Asymptomatic small true aneurysms (<20 mm) can be followed with CTA every 6-12 months — >5 mm growth is an indication for intervention. Ruptured aneurysm requires emergent embolization or surgery — mortality 30-50%.
Treatment is recommended when visceral artery aneurysms are >2 cm or symptomatic. Splenic artery aneurysms carry rupture risk during pregnancy. Mycotic aneurysms require urgent treatment. Treatment options include endovascular embolization or surgery.