May-Thurner syndrome is a condition that causes the left iliac vein in your pelvis to narrow because of pressure from the right iliac artery.

It’s also known as:

  • iliac vein compression syndrome
  • iliocaval compression syndrome
  • Cockett syndrome

The left iliac vein is the main vein in your left leg. It works to carry blood back to your heart. The right iliac artery is the main artery in your right leg. It delivers blood to your right leg.

The right iliac artery 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.

Most people with May-Thurner syndrome don’t experience any symptoms unless it causes deep vein thrombosis (DVT).

However, because May-Thurner syndrome can make it difficult for blood to circulate back to your heart, some people may experience symptoms without DVT.

These symptoms occur predominantly in the left leg and can include:

A 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

Women can also develop pelvic congestion syndrome. The main symptom of pelvic congestion syndrome is pelvic pain.

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. Healthcare providers aren’t sure why this happens.

It’s hard to know how many people have May-Thurner syndrome because it usually doesn’t have any symptoms. However, according to a 2015 study, it’s estimated that 2 to 3 percent of those who develop a DVT can attribute it to May-Thurner syndrome.

Per a 2018 study, May-Thurner syndrome occurs at least twice as often in women compared to men. Additionally, most cases of May-Thurner syndrome occur in individuals between ages 20 and 40, according to a 2013 case report and review.

Risk factors that can increase the risk for DVT in people with May-Thurner syndrome include:

  • prolonged inactivity
  • pregnancy
  • surgery
  • dehydration
  • infection
  • cancer
  • the use of birth control pills

May-Thurner syndrome’s lack of symptoms can make it hard for healthcare providers to diagnose. Your healthcare provider will start by requesting your medical history and giving you a physical examination.

Your healthcare provider will use imaging tests to help see narrowing in your left iliac vein. Either a noninvasive or an invasive approach can be utilized.

Some examples of imaging tests your healthcare provider may perform include:

Noninvasive tests:

Invasive tests:

  • catheter-based venogram
  • intravascular ultrasound, which uses a catheter to perform an ultrasound from the inside of a blood vessel

Not everyone who has May-Thurner syndrome will know that they have it. However, the condition can require treatment if it starts to produce symptoms.

It’s important to know that it’s possible to have May-Thurner syndrome without having DVT.

The reduction in blood flow associated with the narrowing of the left iliac vein can cause symptoms such as:

  • pain
  • swelling
  • leg ulcers

Treatment for May-Thurner syndrome

Treating May-Thurner syndrome focuses on improving the blood flow in the left iliac vein. This treatment method not only helps to relieve symptoms, but it also can lower your risk of developing DVT.

There are a few ways that this can be accomplished:

  • Angioplasty and stenting: A small catheter with a balloon on its tip is inserted into the vein. The balloon is inflated to open the vein. A small mesh tube called a stent is placed to keep the vein open. The balloon is deflated and removed, but the stent stays in place.
  • 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.

Treatment for DVT

If you have DVT due to May-Thurner syndrome, your healthcare provider may also utilize the following treatments:

  • Blood thinners: Blood thinners can help to prevent blood clots.
  • Clot-busting medications: If blood thinners aren’t enough, clot-busting medications can be delivered via a catheter to help break up the clot. It can take anywhere from a few hours to a few days for the clot to dissolve.
  • Vena cava filter: A vena cava filter helps prevent blood clots from moving to your lungs. A catheter is inserted into a vein in your neck or groin and then into the inferior vena cava. The filter catches clots so they don’t reach your lungs. It can’t stop new clots from forming.

DVT is the main complication May-Thurner syndrome causes, 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:

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 healthcare provider 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. It’s important to make sure you know the signs of a pulmonary embolism so you can get immediate help.

If you have chronic symptoms of May-Thurner syndrome, speak with your healthcare provider about your concerns. They can work closely with you to diagnose your condition and advise you on best ways to treat and manage it.