Superior Mesenteric Artery Syndrome (SMAS)

Inherited syndrome associated with vomiting because of compression of the third part of the duodenum by the superior mesenteric artery.

Cast Syndrome.

Acquired, the exact incidence is unknown, but is probably higher than previously thought.

Occasionally, this disorder is seen after body casting or corrective spinal surgery. It presents with clinical features of upper gastrointestinal obstruction and is attributed to extrinsic compression of the third part of the duodenum between the aorta (posteriorly) and the superior mesenteric artery (anteriorly) (decrease in aortomesenteric angle). Symptoms of persistent vomiting with abdominal distention, epigastric tenderness, and tympanic percussion note usually beginning 6 to 8 days after surgery or the application of a body casting, but may occur up to 40 days thereafter. In contrast to postoperative ileus, bowel sounds are usually present in Superior Mesenteric Artery Syndrome (SMAS). It is thought to be more common in the second decade of life when increased spinal flexibility and truncal casting increase lordosis and subsequently alter the anatomic relationship between the superior mesenteric artery, the aorta, and the duodenum. The combination of surgery to correct spinal deformities (most often scoliosis) and generalized weight loss are known risk factors for duodenal obstruction. It is most frequently seen in patients after spinal or pelvic surgery, but has also been described after femoral fractures. Patients with acute SMAS may be severely dehydrated and have profound electrolyte abnormalities. Close monitoring of hydration and serum electrolytes is therefore mandatory, since fatal outcome secondary to severe metabolic alkalosis and electrolyte disturbances has been described. Furthermore, duodenal obstruction has resulted in death from gastric perforation. Contrast radiography is used to demonstrate an abrupt cutoff in the third part of the duodenum representing the external compression by the superior mesenteric artery. A nasojejunal feeding tube (distal to the obstruction) has been used successfully to provide feeds and favoring weight gain, which seems to have a positive effect on SMAS. Alternatively, total parenteral nutrition has been used; however, the enteral way is usually preferred. The left lateral and/or prone position and/or adjusting the body cast may alleviate the symptoms; however, surgery may be necessary in up to half of the patients to resolve the compression (duodenal mobilization with division of the ligament of Treitz or bypass procedures such as duodenojejunostomy or gastrojejunostomy have been used).

Assess and correct hydration, serum electrolyte, and acid-base imbalances preoperatively. A rapid sequence induction technique is recommended, because of the increased risk of gastroduodenal content regurgitation and pulmonary aspiration.