Superior mesenteric artery syndrome

CASE PRESENTATION

A 24-year-old woman with no significant medical history presented to the hospital with complaints of nausea and vomiting for one day. The patient had experienced associated symptoms of abdominal distension, which worsened after meals, for the previous six months. The patient denied weight loss. The laboratory results were unremarkable. On physical examination, her abdomen was soft, with minimal tenderness in the epigastric area without guarding or rigidity. Bowel sounds were heard in all four quadrants, and there were no signs of organomegaly, ascites or asterixis.

DIAGNOSIS

Superior mesenteric artery syndrome

An abdominal computed tomography (CT) scan with contrast revealed the narrowing of the third portion of the duodenum compressed by the superior mesenteric artery (SMA), with dilation of the portion of the duodenum proximal to the compression. An abdominal CT scan and ultrasound with Doppler was used to measure the aortomesenteric (AO) angle and the AO distance. The normal AO angle is between 45° and 60° (1); the AO angle in this patient was 18° (Figure 1). The normal AO distance is between 10 mm and 20 mm (1); the AO distance in this patient was 5 mm to 6 mm (Figures 2 to 4); hence, the diagnosis was consistent with SMA syndrome.

Figure 1.

Longitudinal grey-scale ultrasound image demonstrating an aorta-superior mesenteric artery (SMA) angle of 18°

Figure 2.

Longitudinal grey-scale ultrasound image showing an aorta-superior mesenteric artery (SMA) distance of 6 mm measured at the level of the duodenum

Figure 4.

Axial contrast-enhanced computed tomography scan showing a narrow aorta-superior mesenteric artery (SMA) distance of 5 mm

DISCUSSION

SMA syndrome, also known as Wilkie’s syndrome (2), cast syndrome or AO syndrome, is described as the loss of the intervening mesenteric fat pad between the aorta and SMA, leading to narrowing of the angle between the two vessels, which in turn causes compression of the third portion of the duodenum. The most common cause of SMA syndrome is severe weight loss including trauma, burns, anorexia nervosa and/or after prolonged bed rest (3). Other rare causes of SMA syndrome are surgical correction of scoliosis (4) and a congenitally short ligament of Treitz. Patients with SMA syndrome present with bloating sensation, epigastric pain, abdominal distension, nausea and vomiting. Symptoms may be relieved when patients are in the left lateral decubitus, prone or knee-chest position (2). Diagnostic modalities include abdominal ultrasound with Doppler or abdominal CT (5) with contrast to measure the AO angle and AO distance. The treatment for this syndrome is correction of electrolyte imbalance, decompression of the obstruction via a nasogastric tube and nutritional support. Feeding in such patients is aided by a nasojejunal tube placed beyond the third portion of the duodenum. After initial weeks, and once the patient begins gaining weight, oral feeding should be encouraged. If the weight gain does not improve the symptoms, surgical mobilization of the duodenum after the ligament of Treitz is required. The duodenum is placed to the right of the SMA so it does not lie in the acute angle between the SMA and the aorta (6). A comprehensive history should be obtained, especially weight loss, in patients in whom the clinical suspicion of SMA syndrome is high.

Figure 3.

Sagittal maximum intensity projection image of aorta and superior mesenteric artery (SMA) showing a narrow aorta-SMA angle of 18°

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