What Is May-Thurner Syndrome?

May-Thurner syndrome affects two blood vessels that go to your legs -- and it could make you more likely to have a DVT (deep vein thrombosis) in your left leg.

Your blood vessels carry blood to every part of your body. Your arteries move blood away from your heart, and your veins bring it back. Sometimes, arteries and veins cross over each other. Normally, that’s not a problem. But it is if you have May-Thurner syndrome.

This condition involves your right iliac artery, which carries blood to your right leg, and the left iliac vein, which brings blood out of your left leg toward your heart.

In May-Thurner syndrome, the right iliac artery squeezes the left iliac vein when they cross each other in your pelvis. Because of that pressure, blood can’t flow as freely through the left iliac vein. It’s a bit like stepping part way down on a hose.

The result: You’re more likely to get a deep vein thrombosis (DVT) in your left leg. A DVT is a type of blood clot that can be very serious. It’s not just that it can block blood flow in your leg. It can also break off and cause a clot in your lung. That’s called a pulmonary embolism, and it’s life-threatening.


May-Thurner syndrome is random. It’s not something in your genes that you get from your parents.

The crossover of those blood vessels is normal. But in some cases, they are positioned in a way that the right iliac artery presses the left iliac vein against the spine. That added pressure leaves a narrower opening. It can also lead to scars in the vein.



You likely won’t even know you have it unless you get a DVT. You might get pain or swelling in your leg, but usually, there aren’t any warning signs.

With a DVT, your left leg may show symptoms such as:

  • Changes in skin color, with it looking more red or purple than normal
  • Heaviness, tenderness, or throbbing
  • Pain that feels like a cramp or charley horse
  • Skin that’s warm to the touch
  • Swelling
  • Veins that look larger than usual

If the DVT breaks off and forms a clot in your lungs, you’ll notice:


Your doctor will first do a physical exam to look for signs and symptoms of a DVT. From there, you may need imaging, such as:

  • CT or MRI
  • Ultrasound
  • Venogram, a type of X-ray that uses a special dye to show the veins in your leg


There are two goals: to treat any clots you already have and to keep new ones from forming.

Your doctor may talk to you about several options, including:

Blood thinners . These drugs are commonly used to treat DVT. They can prevent new clots and keep ones you already have from getting bigger. Your doctor may call these medicines anticoagulants.

Clot busters. Doctors may use these to treat more serious clots. You might also hear this treatment called thrombolytic therapy. Your doctor uses a thin tube, called a catheter, to send the medication right to the site of the clot. The drug breaks it down in anywhere from a few hours to a few days.

Angioplasty and a stent. This is a common treatment for May-Thurner syndrome. First, your doctor uses a small balloon to expand the left iliac vein. Then, you get a device called a stent. It’s a tiny cylinder, made of metal mesh, that keeps the vein open wide so blood can flow normally.

Vena cava filter. You might get this if you can’t take blood thinners or if they don’t work well for you. Your doctor places a filter in your vena cava, a large vein in your belly. Although the filter won’t prevent clots from forming, it will catch them before they end up in your lungs.


Bypass surgery. Your doctor builds a new path for blood to flow. You can think of it as a detour around the part of the left iliac vein that’s getting squeezed.

Surgery to move the right iliac artery. This operation shifts the position of the artery so it sits behind the left iliac vein and no longer presses on it.

Tissue sling. With this surgery, you get extra tissue put in that acts as a cushion between the two blood vessels.

WebMD Medical Reference Reviewed by James Beckerman, MD, FACC on January 17, 2018



KidsHealth: “Arteries and Veins.”

University of Virginia Health System: “May-Thurner Syndrome.”

University of Iowa Hospitals and Clinics: “May-Thurner Syndrome.”

Cleveland Clinic: “May-Thurner Syndrome.”

National Blood Clot Alliance: “May-Thurner Syndrome.”

Johns Hopkins Medicine: “What is a venogram?”

Mayo Clinic: “Deep Vein Thrombosis (DVT).”

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