The common iliac veins are major blood vessels located deep within the pelvis. Their primary responsibility is to collect deoxygenated blood from the lower half of the body and begin its transport back toward the heart. This function makes them a component of the body’s venous system, which handles the return of blood for re-oxygenation.
Anatomy and Location of the Common Iliac Vein
The body has a right and a left common iliac vein situated in the pelvic region. Each vein is formed by the joining of the external iliac vein and the internal iliac vein. This union occurs near the front of the sacroiliac joint, at about the level of the fifth lumbar vertebra (L5). The external iliac vein is a continuation of the femoral vein from the thigh and carries blood from the leg.
The internal iliac vein collects blood from the pelvic organs, such as the bladder and reproductive organs, as well as the gluteal muscles. Once formed, each common iliac vein measures approximately 5 to 6 cm in length and travels upward. The two common iliac veins then merge to create the inferior vena cava (IVC), the largest vein in the body, which carries deoxygenated blood from the lower and middle body to the heart.
The common iliac arteries, which supply oxygenated blood to the pelvis and legs, run alongside the veins. Because the inferior vena cava lies to the right of the body’s midline, the left common iliac vein is longer than the right. The left vein must travel across the body, passing behind the right common iliac artery to reach the IVC.
Function in the Circulatory System
The role of the common iliac vein is to serve as a conduit for deoxygenated blood returning from the lower extremities and the pelvic region. Blood that has supplied oxygen to the tissues of the legs is collected into the femoral veins, which then become the external iliac veins.
Simultaneously, the internal iliac veins gather deoxygenated blood from the various organs and structures within the pelvis. The external and internal iliac veins on each side of the body unite to form the left and right common iliac veins, channeling the collected blood into these larger vessels.
From the common iliac veins, the blood continues its journey toward the heart. The right and left common iliac veins merge to form the inferior vena cava. The IVC then transports this deoxygenated blood upward through the abdomen, delivering it directly into the right atrium of the heart, where it is pumped to the lungs for re-oxygenation.
Associated Medical Conditions
Several medical conditions can affect the common iliac veins. One is deep vein thrombosis (DVT), the formation of a blood clot in a deep vein. A DVT in a large vessel like the common iliac vein can obstruct blood flow from the leg and pelvis, leading to symptoms such as leg swelling, pain, and skin discoloration.
Another condition is May-Thurner syndrome, also known as iliac vein compression syndrome. This condition affects the left common iliac vein when the right common iliac artery, which crosses over it, compresses it against the lumbar spine. This constant pressure can lead to irritation and the development of fibrous spurs within the vein, narrowing the vessel and impeding blood flow.
The compression seen in May-Thurner syndrome increases the risk of developing a DVT in the left leg. While many people may have some degree of compression without symptoms, for others it can cause chronic pain, swelling, and other complications related to poor blood drainage from the limb.