SMA Syndrome
Overview
SMA Syndrome (Wilkie's Syndrome) is a rare cause of proximal intestinal obstruction caused by compression of the third part of the duodenum (D3) between the aorta (posteriorly) and the superior mesenteric artery (anteriorly). Loss of the mesenteric fat pad narrows this angle to a critical level.
Pathophysiology
The normal aortomesenteric angle is 38-56 degrees, maintained by mesenteric fat. Severe rapid weight loss (anorexia nervosa, malnutrition, prolonged bed rest, severe burns) reduces this to <25 degrees, mechanically compressing the duodenum.
Imaging Findings
- CT Angiography (Gold Standard): Demonstrates the narrowed aortomesenteric angle (<25 degrees) and/or distance (<8 mm). Dilated stomach and proximal duodenum with abrupt cut-off at D3.
- Barium Study: Abrupt, straight, vertical cut-off of contrast in D3 with massive proximal dilatation. The 'to-and-fro' peristalsis of trapped barium is pathognomonic.
- Positional Relief: Symptoms improve in the prone or left lateral decubitus position (widens the SMA angle).
WarningManagement Principle
Initial treatment is non-operative: nasojejunal tube feeding (bypassing the obstruction), nutritional rehabilitation, and weight gain to restore the mesenteric fat pad. Surgery (duodenojejunostomy or Strong's procedure) is reserved for refractory cases after failure of conservative management.
High Yield Facts
LightbulbFRCR / MD Prep Pearl
Key measurements on CT: aortomesenteric distance <8 mm AND aortomesenteric angle <25 degrees together confirm the diagnosis. Isolated abnormal measurements can be incidental. Must differentiate from a retroperitoneal mass or tumour compressing the duodenum.