Distended left renal vein: CT/sonographic normal variant.

The left renal vein frequently demonstrates a marked variation in caliber between the part distal to the aorta and the part directly in front of the aorta. This is well seen on both computed tomography (CT) and sonography. This variation in caliber or distention is believed to be secondary to a "nutcracker " effect formed by the aorta posteriorly and the superior mesenteric artery anteriorly. The third part of the duodenum may also add to the pincer effect on the left renal vein. A series of 72 patients was examined for this variation and the relation of the caliber of the left renal vein to the anatomy of the aorta, superior vena cava, and duodenum. These patients were also evaluated for any possible relation between the presence of a distended left renal vein and a varicocele.