Superior Mesenteric Artery Syndrome

Superior mesenteric artery syndrome occurs when the third portion of the duodenum is trapped between the superior mesenteric artery anteriorly and the aorta and vertebral column posteriorly. A cushion of retroperitoneal mesenteric fat normally keeps these structures apart. Substantial loss of that fat narrows the aortomesenteric angle and distance, allowing the artery to compress the duodenum. The result is a form of proximal intestinal obstruction. Food, gastric secretions, and bile accumulate above the compressed segment, producing postprandial epigastric pain, early satiety, nausea, abdominal fullness, and often bilious vomiting. Symptoms may improve temporarily in positions that reduce the compression, such as prone or knees-chest positioning. Weight loss can both cause and perpetuate the syndrome. Loss of fat narrows the passage; obstruction then limits intake and causes vomiting, leading to further weight loss. This cycle is why nutritional rehabilitation is not merely supportive—it is directed at restoring the tissue that helps reopen the passage. Common settings include rapid weight loss from anorexia nervosa, malabsorptive disease, cancer or burns; prolonged illness or bed rest; post-bariatric weight loss; and changes in spinal alignment after...