What is Superior Mesenteric Artery (SMA) Syndrome?
Superior mesenteric artery syndrome is a rare condition where the third portion of the duodenum becomes compressed between the superior mesenteric artery and the abdominal aorta, causing upper gastrointestinal obstruction—not to be confused with acute mesenteric ischemia, which is a vascular emergency involving arterial occlusion. 1
Key Distinguishing Feature from Acute Mesenteric Ischemia
This distinction is critical in your patient with morbid obesity, osteoarthritis, and CKD stage 3:
- SMA syndrome presents with chronic, postprandial symptoms and progressive weight loss due to mechanical duodenal compression 1, 2
- Acute mesenteric ischemia presents with sudden severe abdominal pain out of proportion to exam findings, requiring urgent CTA to evaluate for arterial occlusion 1, 3
Pathophysiology
The syndrome results from loss of the mesenteric fat pad between the SMA and aorta, narrowing the aortomesenteric angle to ≤22° and reducing the distance to ≤8 mm 4. This causes extrinsic compression of the duodenum, leading to mechanical obstruction 2, 5.
Clinical Presentation
Cardinal symptoms include: 1
- Postprandial epigastric pain that worsens after meals
- Nausea and bilious vomiting
- Early satiety
- Fear of eating (sitophobia) leading to food avoidance
- Progressive weight loss that perpetuates a vicious cycle by further reducing mesenteric fat 2, 5
The median age is 23 years with female predominance (3:2 ratio), though it can occur at any age 2.
Risk Factors Relevant to Your Patient
Consider SMA syndrome in patients with: 1
- Significant recent weight loss (paradoxically, your patient's morbid obesity history may be relevant if recent weight loss occurred)
- History of gastrointestinal surgery (including bariatric procedures)
- Prolonged bed rest (relevant given osteoarthritis limiting mobility)
- Low BMI in young females
Diagnostic Approach
CT angiography is the standard diagnostic tool measuring the aortomesenteric angle and distance 2, 4. Key diagnostic findings include:
- Aortomesenteric angle ≤22° 4
- Aortomesenteric distance ≤8 mm 4
- Gastroduodenal dilation on barium swallow (57% of cases) 4
- Delayed gastroduodenal emptying (38% of cases) 4
Ultrasound offers advantages in safety and real-time assessment of SMA mobility and duodenal passage 2.
Critical Pitfall to Avoid
Do not allow continued oral feeding in symptomatic patients, as this perpetuates the cycle of weight loss and worsening obstruction 6. Patients with acute symptoms should be made NPO immediately 6.
Management Strategy
Initial Conservative Treatment (Success Rate: 70-80%) 2
- Immediate NPO status during acute presentation 6
- Postural changes (left lateral decubitus or prone positioning)
- Gastroduodenal decompression via nasogastric tube
- Enteral nutrition via nasojejunal tube (preferred route, bypasses obstruction) 6
- Total parenteral nutrition reserved for patients who cannot tolerate nasojejunal feeding 6
Surgical Treatment (Success Rate: 80-100%) 2
Laparoscopic duodenojejunostomy is recommended if conservative therapy fails 2, 4. In a prospective study of 39 patients, duodenojejunostomy (with or without distal duodenum resection) resulted in:
- Significant symptom score improvement (10 vs. 32, p<0.0001) 4
- BMI increase (19.5 vs. 17.8, p<0.0001) 4
- Improvement in gastroduodenal dilation and emptying in 38% at 2 months postoperatively 4
Special Considerations for Your Patient
In the context of CKD stage 3: Do not delay CT angiography for elevated creatinine when clinical suspicion exists, as the risk of missing the diagnosis outweighs concerns about contrast nephropathy 7.
Morbid obesity context: While SMA syndrome classically occurs with low BMI, it can develop in previously obese patients who experience rapid weight loss, particularly after bariatric surgery or prolonged immobility from osteoarthritis 8.
Prognosis
With appropriate treatment, symptoms and quality of life improve significantly, though surgical intervention is not curative in all cases 4. The condition can be potentially fatal if untreated due to aspiration pneumonia, metabolic alkalosis from recurrent vomiting, or severe malnutrition 2, 8.