The superior mesenteric artery takes origin just below the celiac artery, and therefore behind the neck of the pancreas, and therefore behind the splenic vein, which is embedded in the pancreas. It would prevent ascent of the left renal vein, which crosses the aorta close below it. The left renal vein may, indeed, be regarded as clamped between the root of the superior mesenteric artery and the aorta like a nut within nutcrackers. The artery passes caudal and ventral to the left renal vein, the head of the pancreas, and third part of the duodenum and enters the root of the mesentery.
November 2003. Arch Surg. 2003;138(11):1263. doi:10.1001/archsurg.138.11.1263