What is SMA Syndrome?
Superior mesenteric artery (SMA) syndrome, also known as Wilkie's syndrome, is a rare condition where the third portion of the duodenum becomes compressed between the superior mesenteric artery and the abdominal aorta, resulting in proximal intestinal obstruction 1, 2.
Pathophysiology
The syndrome develops when the protective mesenteric fat pad between the SMA and aorta is lost, causing:
- Narrowing of the aortomesenteric angle to less than 22 degrees (normal is 25-60 degrees)
- Reduction of the aortomesenteric distance to less than 10 mm
- This anatomical change leads to extrinsic compression of the duodenum as it passes through this space 3, 2
Clinical Presentation
Patients typically present with:
- Postprandial epigastric pain
- Nausea and vomiting (most common symptoms)
- Weight loss
- Abdominal distension
The presentation can be either chronic (more typical) or acute-onset 4, 5. Look specifically for symptoms that worsen after eating, as food arrival in the gut triggers obstruction 1.
Common Precipitating Factors
SMA syndrome occurs most frequently in patients who have:
- Sudden or severe weight loss (most common trigger)
- Malnutrition or eating disorders (particularly anorexia nervosa) 1, 3
- Debilitating medical conditions leading to loss of retroperitoneal fat 6, 5
Diagnostic Approach
CT angiography is the gold standard, demonstrating:
- Reduced aortomesenteric angle (<22°)
- Decreased aortomesenteric distance (<10 mm)
- Compression at the junction of the second and third portions of the duodenum 7, 2
Upper GI contrast studies show gastric dilation with abrupt contrast cutoff at the third portion of the duodenum. EGD can confirm the compression site 7, 2.
Important Clinical Caveat
The existence of SMA syndrome as a true clinical entity versus a radiological finding remains contentious 1. Some clinicians dispute whether radiological findings of duodenal compression actually cause symptoms or represent a normal anatomical variant. This controversy is particularly relevant because:
- It may be overdiagnosed
- The condition can be both a cause AND consequence of malnutrition
- Surgical benefits are not always predictable 1
Therefore, correlation between radiological findings and clinical symptoms is essential before proceeding with aggressive interventions.
Management Algorithm
Initial approach should always be conservative 2:
- Nutritional rehabilitation via nasojejunal or jejunostomy tube feeding to restore the mesenteric fat pad
- Correct electrolyte abnormalities (hypokalemia is common) 7
- Parenteral nutrition if enteral feeding fails 6
Surgical intervention (duodenojejunostomy) is reserved for cases where conservative management fails 2. This bypass procedure provides durable symptom relief, but the risks must be carefully weighed given the uncertain benefits and potential for persistent nausea from chronic gastric dysmotility 1, 2.
Key Pitfall to Avoid
Delayed diagnosis is extremely common due to nonspecific symptoms 5, 2. Include SMA syndrome in your differential for:
- Young females with eating disorders presenting with obstructive symptoms 3
- Any patient with recent significant weight loss and postprandial pain
- Even acute presentations in otherwise healthy adults without chronic symptoms 4
Early recognition prevents progression to life-threatening complications and reduces psychological distress associated with prolonged undiagnosed illness 2.