**5. Diagnosis**

To diagnose a patient with SMAS traditionally barium meal studies with hypotonic duodenography is being used. A positive diagnosis will include duodenal dilatation, retention of barium with in duodenum, the classical vertical linear impression caused by extrinsic pressure in the third part of duodenum and frequent relief of obstruction in left lateral or decubitus position (Tsirikos , Jeans 2005, Raissi et al 1996). In the past angiographic measurement of the aortomesenteric angle was thought to be a gold standard. An aortomesenteric angle of < 22–25° and a distance of <8 mm correlated well with symptoms of SMAS (Hines et al 1984). Because of its invasive nature, Computed tomography (CT) scan or CT angiogram/MR angiogram have taken over as a gold standard (Tsirikos , Jeans 2005, Lee, Mangla 1978). CT or CT angiogram is also superior to ultrasound because it can measure the reduced aortomesenteric angle and show the gastric and duodenal dilatation at the same time. CT scan will also be helpful in finding the cause of SMAS e.g high insertion of ligament of Trietz or a neoplasia in that region. Upper gastrointestinal endoscopy is essential to rule out mechanical outlet obstruction of stomach or an ulcer (Ylinen et al 1989, Raissi et al 1996).
