The 18-year-old arrived at St Vincent's Hospital Sydney with severe abdominal pain, distension, and vomiting after eating at a buffet. He was not underweight. He stood 181 centimeters, weighed 71 kilograms, and had a body mass index of 22, with no significant medical history and no recent weight loss.
His bloods were alarming: lactate 13.7, pH 7.13, a white cell count over twice normal, and acute kidney injury. The CT scan explained why. His stomach measured 113 by 187 by 350 millimeters, distended all the way down to the pelvis, with a transition point at the third part of the duodenum where the bowel simply stopped. Gas had tracked into the wall of the stomach and into the portal vein, both signs that tissue was dying.
The scan also measured the space the duodenum was passing through. The angle between his aorta and his superior mesenteric artery was 5 degrees. The gap was 6 millimeters.
A nasogastric tube drained 6.5 liters. He improved briefly, then deteriorated within hours. Gastroscopy found widespread mucosal ulceration and necrosis; laparotomy confirmed a globally ischemic stomach with gangrene at the fundus, and surgeons removed the organ entirely, reconstructing with a Roux-en-Y. He spent five days in intensive care and eight on the ward, and recovered. The case was published in the Journal of Surgical Case Reports.
The Angle That Decides Whether Food Can Pass
The third portion of the duodenum runs through a gap. Behind it sits the abdominal aorta. In front of it, branching forward off the aorta, runs the superior mesenteric artery. The duodenum threads between the two like a hose passing through a pair of partly closed scissors.
What holds those scissors open is fat. A cushion of fibrofatty tissue keeps the angle between the two vessels wide, normally between 38 and 65 degrees, with 10 to 28 millimeters of clearance. An angle at or below 22 degrees and a distance at or below 8 millimeters is considered highly sensitive and specific for the diagnosis. The teenager's 5 degrees and 6 millimeters fall far below even that.
Lose the cushion and the duodenum gets pinched. The result is mechanical obstruction of the upper digestive tract: pain after meals, early fullness, nausea, bilious vomiting, distension and weight loss. Because those symptoms describe half the complaints in a gastroenterology clinic, the diagnosis is routinely missed. Published incidence estimates run from about 0.013% to 0.3%.
The syndrome usually turns up in people aged 18 to 35 who have lost weight rapidly, due to catabolic illness, malabsorption, surgery, cerebral palsy, or eating disorders. It also follows spinal correction and body casts. Anatomical quirks contribute too, including a high fixation of the ligament of Treitz or an unusually low origin of the artery.
Importantly, the surgeons do not claim the syndrome caused this particular emergency. They note that several reports describe acute gastric dilatation after buffet meals or binge eating, and conclude that it remains unclear whether the syndrome was the cause or the result of the dilatation. Their hypothesis is that once the stomach ballooned, it pressed on the duodenum and the vessels themselves, creating a closed loop that raised pressure until circulation failed.
When Surgery Itself Sets the Trap
The narrowing does not always come from lost fat. Sometimes an operation distorts the geometry.
Surgeons at a rural hospital in New South Wales described an 88-year-old man with an 18-month history of anorexia, 15 kilograms of weight loss, and intractable vomiting, two decades after an open appendectomy. Initial investigations were inconclusive. Exploratory laparotomy found extensive adhesions putting traction on the superior mesenteric artery through its ileocolic branch, bending the vessel into an acute angle and compressing the duodenum from outside. Releasing the adhesions relieved it, with no bowel resection required. Their report argues the syndrome is under-recognized and that delay invites life-threatening complications.
Other operations do it differently. In a case following ileal pouch-anal anastomosis, a 74-year-old woman developed the syndrome 17 days after major colorectal surgery, with an angle of 36 degrees and a gap of just 2 millimeters. Her surgeons proposed that the pouch procedure stretched the artery and flattened it against the aorta.
The association with restrictive eating disorders is serious and well documented, including a pediatric case of gastric pneumatosis in a child with anorexia nervosa. Symptoms overlap heavily with the eating disorder itself, which delays recognition. That overlap is a reason for specialist care, not for self-assessment.
Treatment Depends on Catching It Early
Most patients do not need a gastrectomy. Conservative management is the standard first move: decompressing the stomach, correcting fluids and electrolytes, and providing nutritional support to rebuild the mesenteric fat pad and restore the angle. Published treatment strategies reserve surgery, usually a duodenojejunostomy that bypasses the compressed segment, for cases that fail conservative care. In the ileal pouch case above, conservative therapy failed, and bypass surgery was performed.
The buffet case sits at the far end. Gastric dilatation with tissue death, gas in the bowel wall or portal venous gas is described in the literature as infrequent and potentially fatal, and gastric ischemia from massive dilatation has been reported elsewhere. Gastrectomy for it has been reported mainly from East Asian countries, and the Sydney team believes theirs is the first Australian case of its kind.
The practical signal for readers is narrow. Persistent vomiting after meals, early fullness and abdominal distension, especially following recent surgery or significant weight loss, deserve medical evaluation rather than watchful waiting. Severe abdominal pain with a rigid or rapidly swelling abdomen is an emergency.
Key Questions Answered
What is superior mesenteric artery syndrome? A rare obstruction in which the third part of the duodenum is compressed between the abdominal aorta behind it and the superior mesenteric artery in front, usually because the fat cushion holding those vessels apart has been lost.
How rare is it? Published incidence estimates range from roughly 0.013% to 0.3%, and several authors note the condition is under-diagnosed.
Do you have to be underweight to develop it? No. The teenager who required a gastrectomy had a body mass index of 22 and no recent weight loss, though rapid weight loss is the classic risk factor.
How can surgery cause it? Adhesions from a previous operation can pull on the superior mesenteric artery and bend it, as documented two decades after an appendectomy. Ileal pouch surgery, colectomy, and spinal correction have also been linked to a narrowed angle.
How is it diagnosed? Contrast-enhanced CT measures the angle between the aorta and the superior mesenteric artery, as well as the distance between them. An angle of 22 degrees or less and a gap of 8 millimeters or less support the diagnosis.
What symptoms should prompt medical attention? Repeated vomiting after eating, early fullness, abdominal pain, and distension, particularly after recent surgery or weight loss. Severe pain with a rapidly distending abdomen needs emergency care.
