Superior mesenteric artery syndrome (SMAS) is a digestive condition that occurs when the duodenum (the first part of the small intestine) is compressed between two arteries (the aorta and the superior mesenteric artery). This compression causes partial or complete blockage of the duodenum. Symptoms vary based on severity, but can be severely debilitating. Symptoms may include abdominal pain, fullness, nausea, vomiting, and/or weight loss. SMAS typically is due to loss of the mesenteric fat pad (fatty tissue that surrounds the superior mesenteric artery). The most common cause is significant weight loss caused by medical disorders, psychological disorders, or surgery. In younger patients, it most commonly occurs after corrective spinal surgery for scoliosis. Delays in diagnosis may result in significant complications. Depending on the cause and severity, treatment options may include addressing the underlying cause, dietary changes (small feedings or a liquid diet), and/or surgery. Symptoms may not resolve completely after treatment.

The most common cause of loss of the mesenteric fat pad is significant weight loss caused by medical disorders, psychological disorders, or surgery. Anatomic abnormalities can also contribute to SMAS. In younger patients, it most commonly occurs after corrective spinal surgery for scoliosis.

There are some reports of familial cases of SMAS, and one report of affected identical twins. This suggests there may be a genetic predisposition to SMAS in some people.

There are also several reported cases of SMAS associated with celiac axis compression syndrome.

There are some reports of familial cases of SMAS, and one report of affected identical twins. This suggests there may be a genetic predisposition to SMAS in some people.

Tests that may be needed to evaluate a person with symptoms of SMAS include abdominal X-rays, upper GI series, ultrasound, arteriography, and computed tomography (CT scan).

Diagnosis is often delayed and this may result in significant complications, including gastric pneumatosis (gas within the walls of the GI tract), accumulation of gas in the portal vein, formation of an obstructing duodenal bezoar (solid mass of indigestible material), or fatalities due to electrolyte abnormalities or gastric perforation.

In severe cases, intravenous (IV) nutritional support and/or a feeding tube may be needed to provide enough calories. Affected people can usually then be started on oral liquids, followed by slow and gradual introduction of small and frequent soft meals as tolerated. Then, regular solid foods may be introduced. Metoclopramide treatment to avoid vomiting may be beneficial for some people.

Surgery may be needed if other treatment strategies do not work. However, other treatment options should usually be tried for at least 4-6 weeks before considering surgery.

Surgery options are:

• Strong’s procedure: Where the duodenum is re-positioned to the right of the superior mesenteric artery
• Gastrojejunostomy: Where the jejune (the part of the intestines that continues with the duodenum) is joined directly to the stomach
• Duodenojejunostomy with or without division or resection of the fourth part of the duodenum.

Other complications that may arise in people with SMAS include:

• Other electrolyte imbalances
• Malnutrition
• Hypotension
• Peptic ulcer disease
• Aspiration pneumonia