A blood clot forms when blood thickens and clumps together, transforming from a liquid to a gel-like or semi-solid state. While blood clotting is a normal process that helps stop bleeding after an injury, clots that form improperly within blood vessels can be dangerous. Iliac vein thrombosis is a specific type of deep vein thrombosis (DVT), where a blood clot develops in one of the iliac veins located in the pelvis.
What is Iliac Vein Thrombosis?
Iliac vein thrombosis involves a blood clot within the iliac veins, large veins deep within the pelvis. These veins collect deoxygenated blood from the lower limbs and pelvic organs, merging to form the inferior vena cava, which transports blood back to the heart.
A clot in an iliac vein obstructs this pathway, preventing blood from returning efficiently to the heart. This can lead to blood pooling in the lower extremity. Anatomical variations can compress these veins, making them more susceptible to clot formation by slowing blood flow and increasing the likelihood of a thrombus developing.
Recognizing Iliac Vein Thrombosis
Iliac vein thrombosis arises from a combination of anatomical conditions and predispositions to blood clot formation. A notable anatomical cause is iliac vein compression syndrome, also known as May-Thurner syndrome, where the left iliac vein is compressed by the overlying right iliac artery. This chronic compression can lead to scarring and narrowing within the vein, making it prone to clot development.
Beyond anatomical factors, general risk factors for deep vein thrombosis also contribute. These include prolonged immobility, such as during long flights or extended bed rest after surgery, which slows blood flow in the legs. Recent surgery or trauma, certain cancers, and hormonal therapies like estrogen-containing birth control or hormone replacement therapy can also increase clotting risk. Genetic predispositions, such as inherited thrombophilias, which make blood more likely to clot, also play a role.
Symptoms often manifest in the affected leg. Common signs include swelling, which can be significant and extend to the entire leg, and pain, often described as a cramping or pulling sensation that may start in the calf and move upward. The skin over the affected area may also appear discolored, ranging from reddish to a bluish tint, and feel warmer to the touch. In severe cases, massive blockages can lead to conditions like phlegmasia alba or cerulea dolens, which are medical emergencies.
How Iliac Vein Thrombosis is Identified
Diagnosis of iliac vein thrombosis begins with a physical examination and a review of the patient’s medical history. The doctor assesses the affected leg for swelling, tenderness, skin color changes, and warmth. Details about recent surgeries, prolonged immobility, or any personal or family history of blood clots are also collected.
Imaging techniques are used to confirm the clot’s presence and precise location. Ultrasound is often the first imaging method due to its non-invasive nature and accessibility. However, diagnosing deep vein thrombosis in the pelvic veins with ultrasound can be challenging due to the depth of these vessels and the presence of overlying structures.
Computed Tomography (CT) venography provides detailed images of the iliac veins, allowing clear visualization of clots and any underlying compression. This technique involves injecting a contrast dye to highlight the veins. Magnetic Resonance (MR) venography offers similar detailed imaging without using ionizing radiation, making it an alternative when radiation exposure is a concern. Both CT and MR venography are valuable for confirming the diagnosis and identifying anatomical issues, such as May-Thurner syndrome.
Addressing Iliac Vein Thrombosis
Treatment for iliac vein thrombosis aims to prevent clot enlargement, stop it from traveling to the lungs (pulmonary embolism), alleviate symptoms, and reduce the risk of long-term complications. Anticoagulant medications, commonly known as blood thinners, form the foundation of treatment. These medications do not dissolve existing clots but prevent new ones from forming and existing ones from growing larger, allowing the body’s natural processes to gradually break down the clot. Patients typically take these medications for several months, or sometimes longer, depending on the cause of the thrombosis.
For more severe cases or significant underlying vein compression, invasive therapies may be necessary. Catheter-directed thrombolysis involves inserting a thin tube directly into the affected vein and delivering clot-dissolving medication precisely to the thrombus. This targeted approach can break down the clot more rapidly than anticoagulants alone.
Following thrombolysis, or in cases of persistent compression like May-Thurner syndrome, stent implantation may be performed. A stent, a small expandable mesh tube, is placed within the vein to hold it open and restore proper blood flow. This procedure addresses anatomical compression and reduces the likelihood of future clot formation.
Despite successful treatment, post-thrombotic syndrome (PTS) can develop in 20% to 50% of individuals who experience deep vein thrombosis. PTS results from damage to the vein valves or persistent obstruction, leading to chronic symptoms in the affected leg. These symptoms can include ongoing pain, persistent swelling, skin discoloration, and in severe instances, skin ulcers. Treatment for iliac vein thrombosis aims to minimize the risk and severity of PTS, improving the patient’s quality of life.