Corpus: Ascending lumbar vein

The ascending lumbar veins are long anastomosing veins that run laterally along the lumbar spine on both sides.

The ascending lumbar veins connect the external iliac, iliolumbar, and lumbar veins with the azygos vein on the right and the hemiazygos vein on the left, facilitating venous flow from the lumbar region to the thorax.

There are two distinct veins: the right ascending lumbar vein and the left ascending lumbar vein. On the right, the azygos vein forms from the junction of the right ascending lumbar vein and the right subcostal vein, typically at the level of L1 or L2, and ultimately drains into the superior caval vein.

On the left, the ascending lumbar vein joins the subcostal vein to form the hemiazygos vein, which empties into the azygos vein. Variations exist, where the hemiazygos vein may arise from only one of these veins, and it may also connect to the renal vein.

In cases of inferior caval vein occlusion, the ascending lumbar veins act as significant collateral vessels, providing an alternative route for venous blood between the upper and lower parts of the body (cavocaval anastomoses).