Because the inferior vena cava is on the right half of the body, the left renal vein is longer than the right one.
Structure
One renal vein drains each kidney.[citation needed] A renal vein is situated anterior to its corresponding accompanying renal artery. The renal veins empty into the inferior vena cava, entering it at nearly a 90° angle.[1]
Due to the right-ward displacement of the inferior vena cava from the midline, the left renal vein is some 3 times longer than the right one (~7.5 cm and ~2.5 cm, respectively).[1]
The anatomical relations of the two renal veins are bilaterally asymmetrical.
Left renal vein
The left renal vein is situated posterior to the splenic vein, and the body of the pancreas.[1] It passes through the angle formed by the abdominal aorta (situated posteriorly), and superior mesenteric artery (situated anteriorly) (increased acuteness of this angle may lead to the left renal vein being "pinched" between the two arteries, with the resulting compression impairng blood flow through the vein, a condition known as nutcracker syndrome). Occasionally, the left renal vein (or accessory left renal vein) passes posterior to the aorta.[1]
Right renal vein
The right renal vein is situated posterior to the descending part of the duodenum.[1]
Variation
There is typically a single renal vein drainin each kidney, but accessory renal veins are commonly encountered; renal vasculature anomalies are more frequent with ectopic kidneys, and almost always present with horseshoe kidney).[4]
In some individuals, the left renal vein passes posterior to the abdominal aorta instead of in anterior to it;[1] this is termed a retro-aortic left renal vein (also known as "The Vein of Schnitker"). If there is both a vein passing in front of and one behind the aorta this is called a circumaortic renal vein. In the case of a left sided IVC and the right renal vein passes behind the abdominal aorta, this is termed a retroaortic right renal vein, which is also known as “The Reverse Vein of Schnitker”.[citation needed]
