Superior Mesenteric Artery Syndrome: Diagnosis and Management
Diagnosis
In a thin young adult with rapid weight loss presenting with postprandial epigastric pain, early satiety, nausea and vomiting, SMA syndrome should be diagnosed using CT angiography as the primary imaging modality, which demonstrates compression of the third portion of the duodenum between the superior mesenteric artery and aorta. 1, 2
Clinical Presentation to Recognize
The characteristic symptom constellation includes:
- Postprandial epigastric pain that worsens after meals 1, 3
- Large volume bilious vomiting 4
- Early satiety and fear of eating (sitophobia) 1
- Progressive weight loss (typically BMI <16) 1, 4
- Nausea and sense of fullness 4, 5
Diagnostic Imaging Algorithm
CT angiography is the gold standard diagnostic test and should demonstrate: 1, 2
- Narrowing of the aortomesenteric angle
- Compression of the third portion of the duodenum between the SMA and aorta
- Dilatation of the proximal duodenum 4
Upper GI series with barium can be used as an alternative, showing delayed passage through the third portion of the duodenum with proximal dilatation 1, 4, 6
Ultrasonography offers advantages in safety and real-time assessment of SMA mobility and duodenal passage 7
Critical Diagnostic Distinction
You must distinguish SMA syndrome from acute mesenteric ischemia, which presents with sudden severe abdominal pain out of proportion to exam findings and bowel emptying (diarrhea or bloody stools), requiring urgent CTA to evaluate for arterial occlusion 1. Do not use anticoagulation in SMA syndrome—this is appropriate only for mesenteric ischemia, not mechanical compression 1.
Management
Initial Conservative Management (First-Line)
Patients presenting acutely should be made NPO immediately, as oral feeding is counterproductive and perpetuates the cycle of weight loss and worsening obstruction 3. Conservative management has a 70-80% success rate and includes: 7
Nutritional support:
- Nasojejunal tube feeding is the preferred route, as it bypasses the obstructed third portion of the duodenum 3
- Total parenteral nutrition (TPN) should be reserved for patients who cannot tolerate nasojejunal feeding 3
- The goal is restoration of the aortomesenteric fatty tissue through weight gain 5
Gastroduodenal decompression via nasogastric tube 7
Postural changes including prone or left lateral decubitus positioning 7
Criteria for Attempting Oral Reintroduction
Oral feeding can only be cautiously attempted after: 3
- Hemodynamic stability is achieved
- Gastric emptying is restored (confirmed by resolution of vomiting and decreased NG output)
- Postprandial pain and vomiting have resolved
- Close monitoring for symptom recurrence is mandatory
Surgical Management (When Conservative Fails)
If conservative management fails after adequate trial, laparoscopic duodenojejunostomy is the recommended surgical procedure with an 80-100% success rate 1, 7. This is superior to gastrojejunostomy, which has lower success rates 8.
Surgical options include: 5, 7, 8
- Laparoscopic duodenojejunostomy (preferred, most frequently used with highest success)
- Open duodenojejunostomy or Roux-en-Y duodenojejunostomy
- Duodenal mobilization with division of the ligament of Treitz
Important Clinical Caveats
The diagnosis is often delayed because symptoms can mimic anorexia nervosa or functional dyspepsia 7. However, whether SMA syndrome is a true clinical entity versus a radiological finding remains contentious among some clinicians, and the benefits of surgery are not always predictable 9. Despite this controversy, the risks of surgery should be very carefully considered, especially given that malnutrition itself can impair gut function 9.
Early diagnosis is critical because recurrent vomiting can lead to aspiration pneumonia or respiratory depression via metabolic alkalosis 7.
The condition typically affects young, thin patients (median age 23 years, female predominance 3:2) with recent significant weight loss, low BMI, or following gastrointestinal surgery 2, 7.