Superior mesenteric artery (SMA) syndrome is an uncommon but well recognized clinical entity characterized by compression of the third, or transverse, portion of the duodenum between the aorta and the superior mesenteric artery. This results in chronic, intermittent, or acute complete or partial duodenal obstruction.  Superior mesenteric artery syndrome was first described in 1861 by Von Rokitansky, who proposed that its cause was obstruction of the third part of the duodenum as a result of arteriomesenteric compression. Some studies report the incidence of superior mesenteric artery syndrome to be 0.1-0.3%.  Approximately 0.013-0.78% of barium upper GI studies evaluating for superior mesenteric artery syndrome support the diagnosis. [3, 4]
Despite the fact that about 400 cases are described in the English language literature, many have doubted the existence of superior mesenteric artery syndrome as a real entity; indeed, some investigators have suggested that superior mesenteric artery syndrome is overdiagnosed because it is confused with other causes of megaduodenum. Nonetheless, the entity (also called cast syndrome) is a well-known complication of scoliosis surgery, anorexia, and trauma. It often poses a diagnostic dilemma; its diagnosis is frequently one of exclusion.
The superior mesenteric artery usually forms an angle of approximately 45° (range, 38-56°) with the abdominal aorta, and the third part of the duodenum crosses caudal to the origin of the superior mesenteric artery, coursing between the superior mesenteric artery and aorta. Any factor that sharply narrows the aortomesenteric angle to approximately 6-25° can cause entrapment and compression of the third part of the duodenum as it passes between the superior mesenteric artery and aorta, resulting in superior mesenteric artery syndrome.
In addition, the aortomesenteric distance in superior mesenteric artery syndrome is decreased to 2-8 mm (normal is 10-20 mm). Alternatively, other causes implicated in superior mesenteric artery syndrome include high insertion of the duodenum at the ligament of Treitz, a low origin of the superior mesenteric artery, and compression of the duodenum due to peritoneal adhesions. [5, 6]
The precise incidence of this entity is unknown. In a review of the literature, approximately 0.013-0.78% of the findings from upper GI tract barium studies support a diagnosis of superior mesenteric artery syndrome.
Delay in the diagnosis of superior mesenteric artery syndrome can result in malnutrition, dehydration, electrolyte abnormalities, gastric pneumatosis and portal venous gas, formation of an obstructing duodenal bezoar, hypovolemia secondary to massive GI hemorrhage, and even death secondary to gastric perforation. [7, 8, 9]
No racial differences have been identified.
More females are affected by superior mesenteric artery syndrome. In one large series of 75 patients with superior mesenteric artery syndrome, two thirds of the cases involved women, with an average age of 41 years; one third of cases involved men, with an average age of 38 years.
The superior mesenteric artery syndrome usually occurs in older children and adolescents. In one report, 75% of the cases occurred in patients aged 10-30 years.
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