A 22-year-old man presented with fullness of abdomen associated with intermittent episodes of vomiting since six months. Except for his asthenic built, there was no positive physical finding on examination. Routine laboratory investigations were within normal limits.

RADIOLOGICAL FINDINGS:

An upper GI series revealed dilatation of the first and second parts of the duodenum with an abrupt vertical cut off at its third part. The mucosal pattern was normal. The obstruction to passage of barium was dramatically relieved in the lateral decubitus position.

Fig. 1	Fig. 2

A contract enhanced CT scan of the abdomen showed a dilated proximal duodenum with abrupt cut off at its third part. The superior mesenteric artery (SMA) was seen to pass anterior to the site of the cut off. This was associated with a narrowed aorta-SMA distance.

Fig. 3	Fig. 4 .

These radiological findings were interpreted as a manifestation of the superior mesenteric artery syndrome.

The patient was operated. Intraoperative findings confirmed the diagnosis of SMA syndrome as the third part of duodenum was seen to be compressed between the aorta and SMA. A Roux-en-Y jejunostomy was performed.

DISCUSSION:

The SMA syndrome is an uncommon, but well recognized, clinical entity characterized by compression of the third or transverse portion of the duodenum against the aorta by the SMA - resulting in chronic, intermittent or acute - complete or partial duodenal obstruction. The SMA 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.

Clinical presentation:

Patients often present with chronic upper abdominal symptoms such as epigastric pain, nausea, eructation, voluminous vomiting (bilious or partially digested food), postprandial discomfort, early satiety, and sometimes - sub acute small-bowel obstruction. The symptoms are typically relieved when the patient is in the left lateral decubitus, prone or knee-to-chest position and they are often aggravated when the patient is in the supine position. An asthenic habitus is noted in about 80% of cases. Abdominal examination may reveal a succussion splash.

Pathophysiology:

The SMA usually forms an angle of approximately 45° (range, 38-56°) with the abdominal aorta. The third part of the duodenum crosses caudal to the origin of the SMA coursing between the SMA and the 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 SMA and the aorta - resulting in the SMA syndrome. In addition, the aortomesenteric distance in SMA syndrome is decreased to 2-8 mm (normal is 10-20 mm). Alternatively, other causes implicated in the SMA syndrome include high insertion of the duodenum at the ligament of Treitz, a low origin of the SMA and compression of the duodenum due to peritoneal adhesions.

The important etiologic factors that may precipitate a narrowing of the aortomesenteric angle and result in chronically recurrent mechanical obstruction include the following:

Imaging Studies: