Position of the superior mesenteric artery on computed tomography and its relationship to retroperitoneal disease.

The superior mesenteric artery (SMA) is constant in its retroperitoneal course and easily identified on computed tomography (CT). In 225 CT examinations, anterior and lateral displacement from a defined normal position of the proximal SMA were assessed and correlated with the presence of retroperitoneal disease. Displacement beyond the left margin of the adjacent vertebral body was always due to disease, whereas an SMA situated to the right of a normal aorta was virtually always normal. Lesser degrees of displacement were not reliably associated with disease. In cases where there was minor SMA displacement but CT appeared normal, clinical follow-up revealed retroperitoneal disease in only three out of 40 patients (7.5%). Minor displacement of the SMA is not a good indicator of occult retroperitoneal disease.