Which of the following statements about the anatomic basis for the syndrome of vascular compression of the duodenum are true?

A. The duodenum is obstructed in its distal third as it crosses over the lumbar vertebral column

B. Structures crossing beneath the superior mesenteric artery include the duodenum, the uncinate process of the pancreas, and the left renal vein.

DISCUSSION: The superior mesenteric artery originates behind the neck of the pancreas at the level of the first lumbar vertebra. It arises from the aorta at an acute angle, usually about 37 degrees in normal patients, through which passes the left renal vein, the uncinate process of the pancreas, and the distal third of the duodenum. The duodenum crosses the lumbar spine from right to left and passes upward. It is at this point of passage of the duodenum upward and over the spine that the obstruction occurs. Arteriographic studies show that the aortomesenteric angle in patients with the syndrome is only about 8 degrees. There is no narrowing of the superior mesenteric artery or disturbance of arterial flow, but the area of duodenal obstruction corresponds to the compression of the bowel by the artery. The duodenal compression may often be relieved by assuming the knee-chest, the left lateral, or even the prone position. Increasing lumbar lordosis, as with hyperextension of the back, exacerbates the problem.