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The aforementioned findings, when interpreted in conjunction with the correlative CT scan, are most consistent with SMA syndrome. A rare, oftentimes acquired, vascular compression disorder, SMA syndrome occurs more frequently in adolescent females. It results from abnormally acute angulation of the SMA, which compresses the third portion of the duodenum, and results in obstructive symptoms. The SMA is normally surrounded by retroperitoneal fat and lymphatic tissue, an insulation that cushions and protects the duodenum from extrinsic compression. Conditions that predispose to rapid weight loss occurs, such as anorexia nervosa, malabsorption, catabolic states (burns, malignancy, or post-operative), increase the risk for SMA syndrome. In effect, this acute drop in retroperitoneal fat reduces the distance and exaggerates the angulation between the SMA and duodenum, causing obstructive symptoms. Patients with a more chronic presentation often complain of early satiety and recurrent vague abdominal pain. The diagnosis is primarily clinical, with radiographic findings usually demonstrating obstruction at the expected anatomic location. Fluoroscopic evaluation typically shows dilatation of the first and second portion of the duodenum, extrinsic compression of the third part, and collapsed distal small bowel at the site where the SMA crosses. CT angiography has the advantage of accurately measuring the aorto-mesenteric angle and distance. Normally, the aorto-mesenteric angle measures 25-60°; the aorto-mesenteric distance is 10-28 mm. These parameters are both reduced with SMA syndrome. Of note, a decreased measurement is not diagnostic on its own, but rather supportive when combined with other clinical and radiologic findings.
Treatment is oftentimes conservative with nasogastric decompression. Hyper-alimentation is routinely encouraged, followed by oral feedings with frequent small meals, in order to increase retroperitoneal fat. Promotility agents have showed variable efficacy. Surgery is reserved for refractory cases: duodenojejunostomy or lysis of the Ligament of Treitz with mobilization of the duodenum.
Although unclear whether our patient had any risk factors for SMA syndrome, the clinical presentation and radiographic findings are convincing. Her diet was gradually advanced, and the obstructive symptoms were alleviated with small frequent meals. The patient was discharged home with close GI follow-up in her home country.
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