May-Thurner syndrome is a condition that causes the left iliac vein in your pelvis to narrow because of pressure from the right common iliac artery. The left iliac vein is the main vein in your left leg. The right iliac artery is the main blood vessel for your right leg. Veins bring the blood back to the heart. Arteries deliver blood to the body.

The right iliac vein can sometimes rest on top of the left iliac vein, causing pressure and May-Thurner syndrome. This pressure on the left iliac vein can cause blood to flow abnormally, which can have serious consequences.

May-Thurner syndrome is also known as iliac vein compression syndrome, iliocaval compression syndrome, or Cockett syndrome.

May-Thurner syndrome doesn’t usually have any symptoms unless it causes deep vein thrombosis (DVT). DVT is a blood clot that can slow or block blood flow in the vein.

Symptoms of DVT include:

  • leg pain
  • tenderness or throbbing in the leg
  • skin that looks discolored, red, or feels warm to the touch
  • swelling in the leg
  • feeling of heaviness in the leg
  • enlarged veins in the leg

DVT from May-Thurner syndrome can also cause venous insufficiency. This makes it difficult for your veins to circulate blood back to your heart.

Symptoms of venous insufficiency include:

May-Thurner syndrome is caused by the right iliac artery being on top of and putting pressure on the left iliac vein in your pelvis. Doctors aren’t sure why this happens.

It’s hard to know how many people get May-Thurner syndrome because it usually doesn’t have any symptoms. DVT related to May-Thurner syndrome is more common in women between the ages of 20 and 40, especially after pregnancy or following a long period of inactivity.

May-Thurner syndrome’s lack of symptoms also makes it hard for doctors to diagnose.

To make a diagnosis, your doctor will start by giving you a physical exam. They may also use some of the following imaging tests to help them make a diagnosis:

May-Thurner syndrome only requires treatment if it starts to produce symptoms.

You may be prescribed blood thinners if you have a blood clot. However, blood thinners may not be enough. A clot-busting medication can be delivered via a catheter directly into the vein near the clot. It can take anywhere from a few hours to a few days for the clot to dissolve.

Depending on your medical history and other conditions, your doctor may suggest a minimally invasive surgical procedure.

Balloon angioplasty and stenting

A small catheter is inserted into the vein. A balloon on the tip of the catheter inflates to stretch the vein. Then, a small mesh tube called a stent is placed in the vein to keep it open so blood can flow freely. The balloon is deflated and removed, but the stent stays in place. Here’s what to expect during recovery.

Vena cava filters

The filter helps to prevent blood clots from moving from your leg to your lungs if for some reason you cannot get blood thinners. A catheter is inserted into a large vein in your neck or groin, then into the inferior vena cava, which is your largest vein. The filter will catch clots from your legs so they don’t reach your lungs. It can’t stop new clots from forming.

Other surgical procedures

Other procedures are more involved and may require general anesthesia or an epidural. You may also need to stay in the hospital for a few days. These surgeries include:

  • Bypass surgery: Blood is rerouted around the compressed part of the vein with a bypass graft.
  • Repositioning the right iliac artery: The right iliac artery is moved behind the left iliac vein so it doesn’t put pressure on it. In some cases, tissue might be placed between the left iliac vein and the right artery to relieve the pressure.

DVT is the main complication caused by May-Thurner syndrome, but it can also have its own complications. When a blood clot in the leg breaks free, it can travel through the bloodstream. If it reaches your lungs, it can cause a blockage known as a pulmonary embolism. This can be a life-threatening condition that requires emergency medical treatment.

Get immediate help if you experience:

  • shortness of breath
  • chest pain
  • coughing up a mixture of blood and mucus

Some of the surgeries associated with May-Thurner syndrome are done on an outpatient basis, meaning you can go home the same day after having them. You should be able to return to normal activities within a few days to a week.

For the more involved bypass surgery, you’ll have some soreness afterward. It may take several weeks to a couple of months to make a full recovery.

Your doctor will instruct you on how often you need to follow up. If you have a stent, you may need an ultrasound check about a week after surgery, plus periodic monitoring after that.

Many people with May-Thurner syndrome go through life without ever knowing they have it. If it causes DVT, there are several effective treatment options. Just make sure you know the signs of a pulmonary embolism so you can get immediate help, if needed.