May-Thurner Syndrome

May-Thurner syndrome is a condition that affects blood flow. It occurs when the right iliac artery, which sends blood to your right leg, presses on the left iliac vein, which carries blood from your left leg to your heart. Some people have no symptoms of May-Thurner syndrome. Others develop deep vein thrombosis (DVT) or blood clots in the legs.


Right iliac artery and left iliac vein in drawing of the pelvis of a person with May-Thurner syndrome.
In May-Thurner syndrome, the right iliac artery (red) compresses the left iliac vein (blue).

What is May-Thurner syndrome?

May-Thurner syndrome is when your right iliac artery presses on (compresses) your left iliac vein. Your right iliac artery is the main blood vessel that carries blood to your right leg. Your left iliac vein is the main blood vessel that carries blood from your left leg back to your heart. May-Thurner syndrome may interrupt typical blood flow through your legs.

Other names for May-Thurner syndrome include:

  • Cockett syndrome.
  • Iliac vein compression syndrome.

How does May-Thurner syndrome affect my body?

May-Thurner syndrome makes it harder for blood to flow back to your heart. Instead, it may pool in your legs and can develop into deep vein thrombosis (DVT). DVT occurs when a blood clot forms in your deep leg veins. DVT symptoms may include:

  • Discolored skin on your leg.
  • Enlarged, swollen leg veins.
  • Pain, throbbing or tenderness in your leg.
  • Swelling and feelings of heaviness in your leg.

Some people assigned female at birth with May-Thurner syndrome may also develop pelvic congestion syndrome. Experts believe pelvic congestion syndrome occurs when problems with the veins in your pelvis cause chronic pelvic pain.

How does May-Thurner syndrome disrupt blood flow?

Your veins and arteries continually carry blood throughout your body. Your arteries take oxygen-rich blood from your heart and deliver it to the tissues throughout your body. When your tissues have received the oxygen and nutrients, your veins carry the oxygen-poor blood back to your heart and lungs.

Your veins and arteries cross over each other at some places in your body. Your right iliac artery crosses over your left iliac vein in your pelvis. This usually isn’t a problem. But in May-Thurner syndrome, the right iliac artery puts pressure on the left iliac vein. The effect is like stepping on a hose. Your left iliac vein compresses, and it’s harder for blood to flow freely through it.

Who is most likely to develop May-Thurner syndrome?

May-Thurner syndrome is slightly more common in women and people assigned female at birth. It’s also more common in adults ages 20 to 50.

How common is May-Thurner syndrome?

Iliac vein compression is common, occurring in about 1 in 5 people. However, many people with iliac vein compression don’t have a formal diagnosis of May-Thurner syndrome. This may be partly because most people don’t have symptoms of May-Thurner syndrome unless they develop DVT.


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Symptoms and Causes

What are the symptoms of May-Thurner syndrome?

Many people don’t have any symptoms of May-Thurner syndrome, especially if they don’t have DVT. Symptoms usually only affect your left leg and may include:

  • Feelings of heaviness.
  • Open sores (ulcers).
  • Pain.
  • Skin discoloration.
  • Swelling.
  • Varicose veins.

What causes May-Thurner syndrome?

May-Thurner syndrome occurs because your right iliac artery presses on your left iliac vein. However, experts aren’t exactly sure why this compression happens.


Diagnosis and Tests

How is May-Thurner syndrome diagnosed?

May-Thurner syndrome diagnosis starts with discussing your health history and symptoms with your healthcare provider. Your provider conducts a physical exam and may use tests that look at your blood vessels, such as:

  • CT scans: Using specialized computers and X-rays to create images of your blood vessels.
  • MRIs: Using magnets, radio waves and specialized computers to create images of your blood vessels.
  • Ultrasounds: Using sound waves to view inside your body.
  • Venograms: Injecting a contrast dye into your veins, then using X-rays to watch how blood flows through your veins.
  • Catheter-based venograms: Inserting a small, hollow tube (catheter) into a vein, injecting contrast dye through the catheter, then using X-rays to watch how blood flows through your veins.
  • Intravascular ultrasounds: Inserting a catheter into your blood vessels, then threading an ultrasound probe through the catheter to get detailed ultrasound images of your blood vessels.

Management and Treatment

How is May-Thurner syndrome treated?

May-Thurner syndrome treatment focuses on improving blood flow and reducing your risk of developing DVT. Your provider may recommend:

  • Angioplasty and stenting: Your provider inserts a catheter with a balloon at the end into the left iliac vein. When it’s in the correct position, the balloon inflates to open the vein. Your provider then places a small mesh tube (stent) in the vein to keep it open and removes the balloon.
  • Bypass surgery: Your provider uses a small piece of tissue from a donor or from another part of your body to build a new route around the compressed portion of the iliac vein. This restores typical blood flow.
  • Surgery to move the right iliac artery: Your provider may perform a procedure to reduce compression on the left iliac vein by moving the right iliac artery. They may place a piece of tissue between the vein and artery to decrease the pressure.


How is May-Thurner syndrome treated if I have DVT?

If you have DVT due to May-Thurner syndrome, your provider may also recommend:

  • Blood-thinning medications, such as anticoagulants, to prevent or break up blood clots.
  • Clot-busting medications, delivered through a catheter to actively dissolve clots.
  • Vena cava filter, a device placed in your inferior vena cava (large vein that takes blood to your heart) that traps blood clots so they don’t move to your lungs.


How can I reduce my risk of May-Thurner syndrome?

There’s no way to prevent May-Thurner syndrome because experts don’t know what causes it. But you can improve your circulation and decrease your risk of blood clots by:

Outlook / Prognosis

Are there complications of May-Thurner syndrome?

The main complication of May-Thurner syndrome is DVT. If a blood clot in your legs breaks off and travels to your lungs, it’s known as a pulmonary embolism.

A pulmonary embolism is a life-threatening medical emergency. Call 911 if you experience any new or worsening symptoms of a pulmonary embolism, including:

What can I expect if I have May-Thurner syndrome?

Many people live long, healthy lives with May-Thurner syndrome. You may not even know you have the condition if you don’t have any symptoms.

Call your healthcare provider if you experience any symptoms of deep vein thrombosis. Many people successfully treat DVT with medications.

Living With

What questions should I ask my healthcare provider?

If you have May-Thurner syndrome or think you could, you may want to ask your healthcare provider:

  • What are the symptoms of May-Thurner syndrome?
  • What is the most likely cause of my symptoms?
  • What tests do I need to diagnose May-Thurner syndrome?
  • What are the symptoms of DVT?
  • What are the symptoms of a pulmonary embolism?
  • What treatment do you recommend for May-Thurner syndrome?
  • What are the chances that symptoms will return after May-Thurner syndrome treatment?

Additional Common Questions

Is May-Thurner syndrome life-threatening?

May-Thurner syndrome can lead to a pulmonary embolism, which is a life-threatening complication. Call 911 immediately if you experience any symptoms of a pulmonary embolism.

How do you tell if you have May-Thurner syndrome?

You may not be able to tell if you have May-Thurner syndrome. Most people don’t know they have the condition unless they develop symptoms of DVT.

The only way to know for sure if you have the condition is to have imaging tests that show your right iliac artery compressing your left iliac vein.

A note from Cleveland Clinic

May-Thurner syndrome occurs when your right iliac artery compresses your left iliac vein. This compression disrupts blood flow and may lead to DVT. Many people have no symptoms of May-Thurner syndrome. Others experience pain, swelling or feelings of heaviness in their legs. Treatment for May-Thurner syndrome focuses on relieving the pressure on your left iliac vein and restoring blood flow.

Medically Reviewed

Last reviewed on 09/07/2022.

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