Superior mesenteric artery syndrome: a vicious cycle
The following case has been reported in BMJ.

A middle-aged cachectic woman with significant medical history of quadriplegia, chronic osteomyelitis, chronic obstructive pulmonary disease, kyphoscoliosis and malnutrition presented with 3 days of persistent nausea and vomiting, absolute constipation and increasing abdominal distention.

She has had similar episodes in the recent past, which were milder in nature, and were diagnosed as gastroenteritis. She was hypotensive (blood pressure 86/60 mm Hg) and tachycardic (130 bpm) on arrival, with a grossly distended abdomen and active vomiting. Initial blood tests detected hypokalaemia (K+ of 3.0 mmol/L), a raised white cell count of 23.4×109/L and features of acute kidney injury. A nasogastric tube was inserted and over a litre of bilious gastric contents was immediately aspirated.

A non-contrast CT scan of the abdomen and pelvis was performed (as the patient is allergic to iodine contrast), which demonstrated marked distension of the stomach and duodenum terminating abruptly where the third part of the duodenum crosses over the aorta. The aortomesenteric distance was approximately 5 mm, with an angle of approximately 11°.

Radiologically, the findings were in keeping with a superior mesenteric artery (SMA) syndrome. Gross distention of the stomach, likely as a result of chronic obstruction, was further compressing and displacing the root of the mesentery along with the SMA, causing a vicious cycle which led to a high-grade small bowel obstruction.

Urgent upper gastrointestinal endoscopy was performed to rule out intraluminal causes of obstruction and insertion of a feeding nasojejunal tube. Due to severe malnutrition, the patient was initially treated concurrently with both enteral and total parenteral nutrition with the aim of expediting recovery and optimising her nutritional state should she require surgery. An open gastrojejunostomy was performed when symptoms failed to improve after 2 weeks. The patient subsequently made an uneventful recovery.

Learning points
• The majority of patients present with chronic abdominal symptoms including nausea and vomiting, postprandial abdominal pain and anorexia. The resulting weight loss further decreases the intervening space surrounding the duodenum.

• Chronic obstruction can result in significant distention of the stomach, which can trigger a vicious cycle where the mesenteric root along with the superior mesenteric artery is further displaced posteriorly, resulting in acute upper intestinal ileus.

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