Imaging description

Superior mesenteric artery syndrome is usually evaluated by contrast-enhanced CT or magnetic resonance angiography (MRA). The classic imaging finding is reduced space between the superior mesenteric artery and the anterior wall of the abdominal aorta that results in duodenal narrowing. The aortomesenteric angle, obtained from sagittal images, is significantly reduced from the normal range of 38–65°. The combination of an aortomesenteric angle less than 22° and an aortomesenteric distance of less than 8–10 mm is considered by some authors to meet criteria for the diagnosis of SMA syndrome in the right clinical setting on CT (Figure 80.1). Additional supportive findings include minimal intra-abdominal and retroperitoneal fat, duodenal compression between the aorta and SMA, dilation of the first and second portions of the duodenum, left renal vein enlargement, and enlargement of the left gonadal vein or other venous collaterals as a result of chronic renal vein compression (Figure 80.1).

Importance

Young age and non-specific symptoms often lead to a delay in diagnosis, resulting in complications such as malnutrition, dehydration, and electrolyte abnormalities in patients with SMA syndrome.

Typical clinical scenario

Superior mesenteric artery (SMA) syndrome is an atypical cause of high intestinal obstruction, with estimated incidence rates based on gastrointestinal barium series from 0.01% to 0.33%. It occurs from an abnormally short distance between the aorta and SMA from loss of intra-abdominal fat, which normally separates them resulting in duodenal compression and is an important differential in patients with postprandial abdominal pain, vomiting, and weight loss. The most common predisposing factors include severe weight loss and cachexia, surgical correction of spinal deformities, and congenital anomalies. Patients with recent bariatric surgery, cancer, or chronic immobilization are at risk.

Common symptoms include intermittent epigastric pain, which is often postprandial, early satiety, nausea, fullness, and voluminous vomiting, most frequently occurring in patients who have experienced rapid weight loss.