Renal vein

The renal vein is a paired vessel (right renal vein and left renal vein) responsible for draining venous blood from the kidney into the caudal vena cava. It emerges from the renal hilum, where it lies ventral (or anterior) to the renal artery and typically cranial to the ureter. The course of the renal vein is generally short and directed medially toward the midline. The right renal vein is shorter than the left due to the position of the caudal vena cava, which runs on the right side of the vertebral column.

In most domestic mammals, each kidney is drained by a single renal vein, but this may vary, especially in large species.

Tributaries

The renal vein receives tributaries from:

• The renal parenchyma

• The adrenal gland (suprarenal vein)

• The ureter

• The left gonadal vein (testicular in the male, ovarian in the female)

There is asymmetry in the drainage of the gonadal and adrenal veins:

• The right adrenal and gonadal veins usually drain directly into the caudal vena cava.

• The left adrenal and gonadal veins often drain into the left renal vein.

Species-specific notes:

Dog and Cat: The renal vein is single and short. The left renal vein often receives both the left adrenal vein and the left gonadal vein. The right adrenal and gonadal veins empty separately into the caudal vena cava. The veins lie close to the renal artery and are surrounded by fat at the renal hilum.

Horse: In the horse, the renal vein can be formed by several tributaries rather than a single trunk, particularly on the left. The adrenal and gonadal veins show the same asymmetrical pattern as in dogs and cats. The renal vein lies deep in the retroperitoneum and is relatively short due to the compact renal hilum.

Ox (Cattle): The renal vein in cattle is longer and may receive multiple tributaries, including lumbar veins. The left renal vein often receives the left adrenal vein, left gonadal vein, and lumbar branches, and may communicate with the left ascending lumbar vein. The right renal vein is usually shorter and simpler.

Sheep and Goat: Similar in pattern to the ox, but typically with fewer tributaries. The left renal vein generally receives the adrenal and gonadal veins, while the right ones often drain separately into the caudal vena cava.

Pig: The renal veins are short and thick, entering the caudal vena cava at the level of the second lumbar vertebra. Both left and right adrenal and gonadal veins usually drain into their respective renal veins. There is less asymmetry compared to other species.