Common iliac vein

The common iliac vein is a large, paired blood vessel that is formed at the level of the sacroiliac joint by the union of the external iliac vein and the internal iliac vein. The external iliac vein (Read more!) is the cranial continuation of the femoral vein and is responsible for transporting venous blood from the lower limb. The internal iliac vein (Read more!) collects blood from the pelvic cavity and gluteal region, running alongside the internal iliac artery. Overall, the common iliac veins drain venous blood from the lower limbs and pelvis into the inferior vena cava.

The right common iliac vein is shorter and follows a more vertical path. It lies lateral to the right common iliac artery. In contrast, the left common iliac vein is longer and follows a more oblique course, lying medial to the left common iliac artery. Both common iliac veins ascend and unite at the level of the fourth or fifth lumbar vertebra (L4 or L5) to form the inferior vena cava (Read more!). This union occurs slightly to the right side of the midline, and the inferior vena cava then carries venous blood to the right atrium of the heart.

Along their course, the common iliac veins receive several tributaries. Both typically receive the iliolumbar veins (Read more!), and occasionally the ascending lumbar veins (which may also drain into the iliolumbar veins, azygos vein, or hemiazygos vein). The left common iliac vein additionally receives the unpaired median sacral vein (Read more!), which drains the sacral region.

Note: The common iliac veins typically lack valves, which are normally present in veins to prevent backflow of blood.