Basics of May-Thurner Syndrome

May-Thurner syndrome—also called iliac vein compression—occurs when the right iliac artery crosses over the left iliac vein. Occasionally, this can lead to compression of the iliac vein at that location. This change in anatomy increases the chance of developing a deep vein thrombosis (DVT).

A doctor talking with her patient in the office
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Symptoms of May-Thurner Syndrome

Symptoms of May-Thurner syndrome can include pain and/or swelling, though in many cases there are no symptoms. Symptomatic May-Thurner syndrome occurs more commonly in women in their 20s and 30s. Often it is diagnosed during the treatment of DVT.

Increased Risk of Blood Clots

Compression of the left common iliac vein causes irritation/injury to the blood vessel, resulting in the 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, such as hormonal contraception (birth control pills) or prolonged inability to walk after surgery, may further increase this risk.


May-Thurner syndrome is typically diagnosed with imaging tests such as color Doppler ultrasound, computed tomography angiography, 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.

Diagnosis of May-Thurner syndrome is often followed by a workup (sometimes called a “hypercoagulable workup”) 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, because the clot must be removed to prevent the development of post-thrombotic syndrome. Treatment with “clot-buster” medication like tissue plasminogen activator (tPA) is often required at the time of diagnosis; tPA is usually delivered via a catheter directly to the area of the clot.

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 and stent placement) may occur at the same time as intravascular ultrasound, allowing confirmation of the diagnosis and definitive treatment.

Anticoagulation treatment will be generally be continued for a few months after stent placement, but it may not be required long term.

6 Sources
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  4. American Heart Association. Understand your risk for excessive blood clotting.

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  6. Meissner MH, Gloviczki P, Comerota AJ, et al. Early thrombus removal strategies for acute deep venous thrombosis: clinical practice guidelines of the Society for Vascular Surgery and the American Venous Forum. J Vasc Surg. 2012;55(5):1449-1462. doi:10.1016/j.jvs.2011.12.081

By Amber Yates, MD
Amber Yates, MD, is a board-certified pediatric hematologist and a practicing physician at Baylor College of Medicine.