Pathophysiology
Clinical meaning
Superior mesenteric artery (SMA) syndrome is a rare vascular compression disorder in which the third portion of the duodenum is compressed between the SMA anteriorly and the aorta and vertebral column posteriorly. The aortomesenteric angle (normally 38-65 degrees) narrows to less than 25 degrees, and the aortomesenteric distance (normally 10-28 mm) decreases to less than 8 mm, typically due to loss of the mesenteric fat pad that normally maintains the angle. This occurs in conditions causing significant weight loss (anorexia nervosa, malabsorptive states, burns, cancer, body casting, prolonged bed rest, spinal surgery correction of scoliosis). The duodenal compression causes intermittent or complete gastric outlet obstruction with postprandial epigastric pain, nausea, bilious vomiting, early satiety, and progressive weight loss โ creating a vicious cycle where weight loss worsens the compression. Wilkie first described the syndrome in 1927. The cast syndrome variant occurs after body casting for scoliosis or spinal fractures, where the cast forces the spine into hyperextension, acutely narrowing the aortomesenteric angle.