Superior Mesenteric Artery Syndrome

Superior mesenteric artery (SMA) syndrome is compression of the third part of the duodenum between the SMA and the aorta, causing proximal duodenal obstruction.

• Normal aortomesenteric angle is 38 to 65 degrees and the aortomesenteric distance is 10 to 28 mm. Syndrome occurs with angle under 22 to 25 degrees and distance under 8 to 10 mm.
• Cause is loss of the retroperitoneal fat pad due to rapid weight loss: anorexia nervosa, malignancy, burns, trauma, chronic illness, malabsorption, bariatric surgery, prolonged bed rest, spinal surgery (scoliosis correction), body cast (cast syndrome).
• Rare: congenital short ligament of Treitz, abdominal aortic aneurysm, lumbar lordosis.
• Incidence 0.1 to 0.3%, young women most often.
• Complications: dehydration, electrolyte abnormalities, malnutrition, gastric perforation, aspiration, hypokalaemic metabolic alkalosis.

• Postprandial epigastric pain and fullness, early satiety, nausea, bilious vomiting, weight loss.
• Pain relieved by knee to chest position, prone, or left lateral decubitus position, and worsened lying supine.
• Acute presentations with complete obstruction: distension, severe vomiting.
• Examination: epigastric distension, succussion splash, cachexia.

• Upper gastrointestinal contrast study: abrupt vertical linear cut off of contrast in the third part of the duodenum, dilated proximal duodenum with antiperistaltic waves, delay of 4 to 6 hours.
• CT angiography or MR angiography is diagnostic: aortomesenteric angle under 22 degrees, distance under 8 mm, with duodenal dilatation.
• Upper endoscopy to exclude intraluminal obstruction (extrinsic compression may be seen).
• Laboratory: electrolytes (hypokalaemia, hypochloraemia, metabolic alkalosis), albumin, magnesium, phosphate, haemoglobin.
• Exclude other causes of duodenal obstruction (pancreatic tumour, annular pancreas, duodenal web) and assess underlying cause of weight loss.

Conservative (first line, success 60 to 80%)

• Correct fluid, electrolyte and nutritional deficits; gastric decompression with nasogastric tube.
• Nutritional rehabilitation: nasojejunal tube feeding beyond the obstruction (placed endoscopically or fluoroscopically) with a hypercaloric formula, advance to 30 to 35 kcal/kg/day; parenteral nutrition if enteral access fails.
• Positioning: left lateral or prone after meals; small frequent liquid or semi solid meals.
• Prokinetics (metoclopramide 10 mg before meals, erythromycin 250 mg) as adjuncts; antiemetics (ondansetron 4 mg).
• Treat the underlying cause (eating disorder with psychiatric care, malignancy, spinal cast release).
• Refeeding syndrome precautions: thiamine 100 mg, start at 10 to 15 kcal/kg/day, monitor phosphate, potassium, magnesium.

Surgical (failure of 4 to 6 weeks of conservative therapy, severe complications)

• Laparoscopic duodenojejunostomy (success over 90%), the standard.
• Alternatives: Strong procedure (division of the ligament of Treitz and duodenal mobilisation), gastrojejunostomy (risk of blind loop syndrome).
• Endovascular SMA stenting or duodenal stenting are not recommended.
• Follow up with weight, nutritional parameters and symptom resolution. Recurrence is uncommon if weight regained.