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).