Corpus: Common iliac vein

The common iliac vein is a large, paired vein that forms on both sides from the confluence of the external iliac vein and the internal iliac vein.

The common iliac vein ascends cranially and medially, accompanying the common iliac artery. At the level of the 5th lumbar vertebra, the left and right common iliac veins merge to form the inferior vena cava, a location known as the venous bifurcation. Since the inferior vena cava is offset to the right of the midline, the left common iliac vein is slightly longer than the right.

• Iliolumbar vein

The left common iliac vein can occasionally be compressed by the right common iliac artery, leading to vena iliaca compression syndrome, also known as May-Thurner syndrome.