Superior Mesenteric Artery Syndrome (SMA Syndrome), sometimes called Wilkie’s syndrome, is a rare gastrointestinal disorder. It occurs when the third part of the duodenum becomes obstructed due to external compression from two major abdominal blood vessels. Although uncommon, the syndrome presents a diagnostic challenge because its symptoms often mimic those of more frequent digestive conditions.
The Underlying Mechanism
The obstruction arises from an anatomical pinch point in the upper abdomen. The third portion of the duodenum passes through a narrow space created by the abdominal aorta (Ao) behind it and the Superior Mesenteric Artery (SMA) arching over it. Normally, the SMA branches from the aorta at a wide angle, typically 38 to 65 degrees. This angle is maintained by a protective layer of retroperitoneal and visceral fat tissue that acts as a cushion, keeping the vessels separated.
In SMA Syndrome, the angle between the aorta and the SMA significantly narrows, often falling to 6 to 25 degrees. This loss of the protective fat pad allows the SMA to press down on the duodenum, trapping it against the aorta and causing a partial or complete blockage. The distance between the two vessels, normally 10 to 28 millimeters, decreases to 2 to 8 millimeters.
The most frequent trigger for the loss of this fat cushion is rapid or significant unintentional weight loss. This can be due to underlying illnesses, trauma, or certain surgical procedures. Once the protective fat is diminished, the decreased aortomesenteric angle causes duodenal compression, leading to a cycle of vomiting, reduced food intake, and further weight loss.
Identifying Signs
Duodenal obstruction leads to digestive symptoms centered around food intake. Patients often report postprandial nausea and vomiting of partially digested food, which results from the physical blockage preventing the stomach and duodenum from emptying properly.
A hallmark symptom is severe abdominal pain, commonly localized to the epigastric region (upper abdomen). This pain is exacerbated by eating and accompanied by early satiety. The pain tends to worsen when the patient lies on their back (supine position) because this posture further tightens the angle of compression. Relief is often found by adopting specific positions, such as lying on the left side (left lateral decubitus) or assuming a prone, knee-to-chest position, which manually shifts the small bowel mesentery and alleviates pressure. The inability to absorb sufficient nutrients often leads to progressive unintentional weight loss.
Confirmatory Testing
Diagnosis requires reviewing symptoms and using specialized imaging studies to visualize the anatomical compression. An initial diagnostic tool is the Upper GI Series with contrast, where the patient swallows a liquid that coats the digestive tract. This test reveals dilation of the first and second parts of the duodenum, followed by an abrupt cut-off where the compression occurs. Delayed emptying of the contrast material is a strong indicator of obstruction.
Cross-sectional imaging, particularly Computed Tomography (CT) angiography or Magnetic Resonance Imaging (MRI), provides the most definitive evidence. These scans allow physicians to directly measure the two key pathological parameters. CT criteria for diagnosis typically include an aortomesenteric angle of less than 22 degrees and an aortomesenteric distance of less than 8 to 10 millimeters. Imaging also helps rule out other causes of duodenal obstruction, such as tumors or ulcers.
Restoring Function
Management of Superior Mesenteric Artery Syndrome begins with a conservative, non-surgical approach. The primary goal is nutritional rehabilitation to restore the retroperitoneal fat pad. High-calorie, nutrient-dense meals are prescribed, and if oral intake is insufficient, nutritional support may involve tube feeding (enteral nutrition) or intravenous feeding (Total Parenteral Nutrition or TPN). Weight gain increases the fat cushion, widening the aortomesenteric angle and relieving the duodenal compression.
Postural therapy is a non-operative strategy to reduce symptoms after eating. Patients are advised to lie in the left lateral decubitus position or assume a prone position following meals. If conservative measures fail or symptoms persist despite adequate nutritional support, surgical intervention becomes necessary. The most common and successful procedure is a Duodenojejunostomy. This operation bypasses the compressed segment by creating a new connection between the duodenum and the jejunum, effectively rerouting the flow of food.