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May-Thurner Syndrome

Diagnosis and Treatment of May-Thurner Syndrome
(Iliac vein compression syndrome)

What is May-Thurner Syndrome?

May-Thurner syndrome, or iliac vein compression syndrome, occurs when the right common iliac artery crosses over the left common iliac vein, compressing it between the artery and spine. This change in the anatomy increases the chance of developing a deep vein thrombosis (DVT).

Symptoms of May-Thurner Syndrome

All people with May-Thurner syndrome will not have symptoms secondary to the compression of the left common iliac vein. Sometimes, it is discovered by accident when imaging (particularly CT scan or MRI) is performed for other reasons. Most of the time it is discovered during the work-up of a DVT of the left leg. Symptoms can include pain and/or swelling. May-Thurner syndrome occurs more commonly in women aged 20 to 50 years.

Increased Risk of Blood Clots

Compression of the left common iliac vein causes irritation/injury to the blood vessel, resulting in thickening of the blood vessel wall. This thickening of the blood vessel wall causes pooling of the blood (also called stasis), which increases the risk of clot formation. This risk factor combined with other risk factors for clot formation, like hormonal contraception (birth control pills) or prolonged inability to walk after surgery, may further increase this risk.

Diagnosing May-Thurner Syndrome

Diagnosing May-Thurner syndrome can be difficult based on the location of the blood vessels. Most blood clots in the arms and legs can be easily seen on Doppler ultrasound, but the blood vessels of the pelvis are not.

May-Thurner syndrome should be considered as the cause for an unprovoked (without known cause like trauma or infection) blood clot in the left leg, particularly if there has been more than one clot in the left leg.

Diagnosis generally requires more specific imaging of the pelvic blood vessels, such as CT (CAT) venography or magnetic resonance venography (MRI of the veins). Intravascular ultrasound (ultrasound within the blood vessel) can be very helpful in visualizing the compression of the left common iliac vein.

After discovering May-Thurner syndrome, we recommend a work-up looking for other risk factors for clot formation. 

Treatment Options

If a blood clot is present, treatment with anticoagulation is required. Unfortunately, long-term treatment with anticoagulation (blood thinners like heparin, enoxaparin, or warfarin) is not sufficient to prevent further clot formation. Treatment with "clot buster" medication like tissue plasminogen activator (tPA) or thrombectomy (mechanical removal of the clot) are often required at the time of diagnosis.

Treating the blood clot is only one part of the treatment. Removing the blood clot will not treat the underlying problem of the left common iliac vein being compressed, putting it at high risk of clot formation. To prevent further blood clot formation, a stent, a small wire mesh, may be placed to keep the vein open. These treatments (tPA, thrombectomy, placement of a stent) may occur at the same time as intravascular ultrasound allowing confirmation of the diagnosis and definitive treatment.

In the immediate period (up to 3-6 months) after stent placement, anticoagulation treatment will be continued but may not be required long-term.