What Is May-Thurner Syndrome?

May-Thurner Syndrome (MTS)—also known as iliac vein compression syndrome—is a vascular (blood vessel) condition that causes problems with blood flow in the legs. The condition occurs when the right iliac artery in your pelvic area presses the left iliac vein against the vertebrae in your lower back. This action can disrupt normal blood flow from the leg to the heart and increase the risk of developing a blood clot in your deep veins (also known as deep vein thrombosis).

About 2% to 3% of the population has a diagnosis for MTS, which primarily affects people assigned female at birth between the ages of 20 and 50. However, evidence suggests that up to 22% of people may live with the condition, which is widely underdiagnosed because it often causes no symptoms. When symptoms do occur, they may include dull aching, swelling, or a feeling of heaviness in the affected leg.

Symptoms

Many people with MTS do not develop symptoms unless they develop a blood clot in the affected leg, called deep vein thrombosis (DVT). If you develop symptoms of MTS, you usually experience them in the left leg. These symptoms may include: 

• Swelling, heaviness, or fullness in the leg
• Dull aching, tenderness, or throbbing in the leg 
• Varicose veins, particularly in the upper leg
• Skin discoloration, such as redness or purple spots
• Ulcers (open sores)
• Lower back pain 
• Chronic pelvic pain

Causes

May-Thurner syndrome occurs when the right iliac artery compresses (or presses down on) the left iliac vein. The left iliac vein carries blood from your legs to the heart. Compression of this vein causes the blood vessel to narrow, leading to restricted blood flow. 

The exact cause of MTS is unknown, but experts suggest anatomical differences in the positioning of the arteries and veins in the pelvis may play a role. These changes in positioning may be present from birth or develop over time due to various factors, such as pregnancy.

Risk Factors

While anyone can develop MTS, some factors can increase your risk of the condition, including:

• Sex: People assigned female at birth are five times more likely than people assigned male at birth to develop the condition
• Age: MTS primarily affects people between 20 to 50 years old
  

May-Thurner syndrome also increases the risk of developing deep vein thrombosis (blood clots) in the affected leg. You may be at an increased risk of developing blood clots if you:

• Are pregnant
• Use oral contraceptives (birth control pills)
• Recently had surgery
• Don't drink enough water or experience dehydration

Diagnosis

Diagnosing MTS involves a review of your symptoms and medical history, a physical examination, and diagnostic tests. During the physical exam, your healthcare provider will look for signs of compression of the left iliac vein, such as swelling or varicose veins. They also look for signs of a blood clot, such as skin discoloration, pain, and skin that feels warm to the touch on the affected leg. 

If your healthcare provider suspects you have MTS, they will order tests to confirm the diagnosis, which may include:

• Venous duplex ultrasound: Uses sound waves to create images of the blood vessels in the legs and records the sound of blood moving through your arteries and veins. This test helps visualize blood flow through your leg(s) and identify blood clots or narrowed blood vessels.
• Multi-detector computed tomography (MDCT) venography: MDCT involves injecting a contrast dye into one of your veins and taking X-rays of your pelvic region and legs. The MDCT creates highly detailed images of the blood vessels to look for signs of vein compression, damage to blood vessels, and blood clots. 
• Magnetic resonance venography (MRV): Uses magnets, radio waves, and intravenous contrast dye to create detailed, three-dimensional images of your veins.
• D-dimer blood test: Measures the D-dimer level in your blood, which is a protein fragment that gets released into your bloodstream when a blood clot breaks down. High levels of D-dimer may indicate the presence of a blood clot.

Stages of May-Thurner Syndrome

May-Thurner syndrome is a progressive condition that develops slowly through three stages. Staging helps healthcare providers determine the extent of the condition and guides treatment decisions.

• Stage 1: Compression of the left iliac vein with no changes or damage to the vein. This stage is usually asymptomatic (meaning, you have no symptoms).
• Stage 2: Iliac vein compression causes venous spurs (formations of fibrous tissue that develop in the walls of veins) that can restrict blood flow. This stage is also often asymptomatic. 
• Stage 3: The iliac vein is severely compressed, causing deep vein thrombosis, swelling, and varicose veins. 

Treatment

The goal of MTS treatment is to improve blood flow in the affected leg, relieve symptoms, and prevent blood clots. There are a variety of treatments that can effectively manage the condition. Your treatment options will vary depending on your symptoms and whether or not you have a blood clot. 

Medical Procedures

If you have May-Thurner syndrome and no signs of blood clots, treatment focuses on restoring blood flow through the compressed left iliac vein. The most common medical procedure is angioplasty and stenting.

During this procedure, your provider will insert a catheter with a balloon into the left iliac vein to widen the narrowed vein. Once the vein is open, your provider will then place a stent (a tiny mesh tube) into it to keep it open and promote healthy blood flow.

If angioplasty and stenting don't work effectively, your healthcare provider may recommend more invasive procedures such as bypass surgery—although this is rare.

Medications

If MTS causes you to develop deep vein thrombosis, treatment focuses on breaking up existing blood clots and reducing the risk of forming blood clots. Your treatment options may include:

• Anticoagulants: Also known as blood thinners, anticoagulant drugs such as Lovenox (heparin), Coumadin (warfarin), and Eliquis (apixaban) can help slow the body's blood clotting process to help prevent the formation of clots.
• Thrombolytics: Commonly known as clot-busters, thrombolytic drugs are typically administered via a catheter, which delivers the drug directly to a blood clot to dissolve or break it up quickly. Tissue plasminogen activator (tPA) is the most common medicine of this drug type.
  

If these medications are not effective, your healthcare provider may recommend placing a filter inside the inferior vena cava (a large vein that delivers blood to your heart). The placement of a vena cava filter aims to trap an embolus (which is a blood clot that breaks away from the vein it formed in and travels through the vein) to prevent the blood from reaching the lungs.

Compression Socks

Compression socks are stretchy socks that gently squeeze your legs to help improve blood flow and prevent blood clots. If you have early-stage May-Thurner syndrome, this may be the only treatment your healthcare provider recommends unless you develop troubling symptoms or signs of a blood clot.

How to Prevent May-Thurner Syndrome

There is no guaranteed way to prevent MTS, but there are things you can do to reduce your risk of complications and keep your veins healthy. This includes:

• Move your body: Physical activity helps improve blood flow and reduces the risk of blood clots. 
• Avoid prolonged periods of sitting or standing: The risk of blood clots increases when you sit or stand for long periods. If you have a desk job that requires sitting most of the day, get up and stretch your legs every hour. If you are on your feet most of the day, take breaks to sit and elevate your feet.
• Stay hydrated: Drinking water helps promote healthy blood flow and prevents blood from thickening. 
• Maintain a weight that's right for you: Extra body weight puts extra pressure on the veins in the pelvis and legs, which can increase the risk of blood clots. 
• Quit smoking: Smoking damages blood vessels and increases the risk of blood clots.
• Eat nutritious meals: Consuming a balanced diet with plenty of fruits, vegetables, lean proteins, and whole grains helps keep your cardiovascular system (heart) healthy and supports your overall health. 
  

Related Conditions 

People with MTS are more likely to develop health conditions that affect the veins. These include:

• Deep vein thrombosis (DVT): Compression of the left iliac vein impairs blood flow from the legs to the heart and increases the risk of deep vein thrombosis. DVT is the term for blood clots that form in the deep veins of your pelvis and leg. 
• Chronic venous insufficiency (CVI): CVI occurs when blood flow in the veins becomes impaired. With May-Thurner syndrome, CVI causes blood to pool in the legs rather than flow from the legs to the heart. 
• Pulmonary embolism (PE): In some cases, DVT associated with May-Thurner Syndrome can lead to a pulmonary embolism, a potentially life-threatening condition in which a blood clot travels to the lungs. 
• Post-thrombotic syndrome (PTS): People with May-Thurner Syndrome with a history of DVT have an increased risk of developing post-thrombotic syndrome, a chronic condition that causes pain, swelling, and skin changes. 

Living With May-Thurner Syndrome

Research shows that most people with May-Thurner syndrome have a good quality of life and average life expectancies with treatment. When you have May-Thurner syndrome, the most important things you can do to prevent complications are following your treatment plan and adopting healthy lifestyle choices that support your overall health. This includes staying physically active, eating nutritious meals, and avoiding smoking.

You may find it helpful to wear compression stockings, especially when traveling, standing, or sitting for long periods. Elevating your legs at the end of the day can also help improve blood flow and reduce swelling. Talk to your healthcare provider if you develop new symptoms, have signs of a blood clot, or want to make adjustments to your treatment plan.