May-Thurner Syndrome

Medically Reviewed by Dany Paul Baby, MD on April 19, 2022
Written by William Moore
4 min read

May-Thurner syndrome, also known as iliac vein compression syndrome or Cockett's syndrome, affects two blood vessels that go to your legs. 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 partway 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 can be life-threatening.

May-Thurner syndrome is random. It isn’t 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’re more likely to get May-Thurner syndrome if you:

  • Are female
  • Have scoliosis
  • Just had a baby
  • Have had more than one child
  • Take oral birth control
  • Are dehydrated
  • Have a condition that causes your blood to clot too much

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 may notice:

Call 911 if you have any of these symptoms.

Your doctor will first do a physical exam to look for symptoms of a DVT. From there, you may need lab tests or imaging tests, 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:

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. The doctor may also use intravascular ultrasound to help put the stent in place.

Blood thinners. These drugs are often 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.

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.

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.

Compression stockings. If your symptoms are mild and the doctor doesn’t think you need more treatment, they may suggest you wear these tight stockings that go from toes to knee. They put pressure on your lower legs that eases swelling and improves blood flow. You may have heard them called support hose.

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.

Surgical thrombectomy. This procedure to remove the clot is reserved for very large clots or those that are causing severe tissue damage.

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

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.

DVT is the primary complication of May-Thurner syndrome, but you could also get:

Pulmonary embolism: If the clot or part of the clot breaks loose, it could move to your lungs. Once there it might block an artery. This condition can be life-threatening.