An adrenal gland is situated at the upper pole of each kidney. While the arterial supply is accomplished by many small vessels, the venous drainage is only through one vein. On the right side the adrenal vein empties directly into the inferior vena cava (the large vessel transporting blood from the lower body to the heart). In contrast, on the left side the adrenal vein empties into the kidney vein, which in turn drains to the inferior vana cava. Due to these anatomical differences a left-sided removal of a kidney always necessitates an interruption of the left adrenal vein, while a right-sided kidney removal does not.