May-Thurner Syndrome: Symptoms, Diagnosis, Treatment

May-Thurner syndrome starts when an artery presses on a pelvic vein. It most often affects blood returning from the left leg^2,4.

Some people have this vein pressure without symptoms or blocked flow^1,9. In others, severe narrowing may lead to deep vein thrombosis, or DVT^2,9.

DVT is a blood clot inside a deep vein^4,9. This guide covers symptoms, tests, treatment choices, and urgent warning signs.

May-Thurner syndrome is also known as iliac vein compression syndrome^1,5. The iliac veins carry blood from the legs toward the heart⁴.

In the classic pattern, the right common iliac artery crosses the left common iliac vein^1,2. It presses the vein against the lower spine^1,2.

This pressure can slow blood returning toward the heart^2,4. Blood may then pool within the affected leg^4,9.

The artery’s pulse may damage the inner wall of the vein. Fibrous bands or spurs may then form inside the vein.

These changes can create lasting narrowing and raise pressure within the vein^2,3. They can also increase the risk of DVT^2,3.

Right-sided and other patterns have also been reported^1,2. However, the classic form affects the left common iliac vein^1,2.

Some degree of left iliac vein compression is common^1,4. Many people have no symptoms or problems with blood flow^1,9.

Some experts call symptom-free compression “May-Thurner anatomy”¹. They use “May-Thurner syndrome” when the compression harms blood flow¹.

An imaging finding alone may not mean that treatment is needed^1,9. Care depends on symptoms, blood flow, clots, and scan results^1,5.

The true rate remains unclear because many people have no symptoms^1,2. May-Thurner syndrome also may go undiagnosed^1,2.

This condition may cause about 2% to 5% of all DVT cases^2,3. It appears more often in studies of people with left-sided iliofemoral DVT.

Iliofemoral DVT can involve a large clot burden in the upper leg veins. Without proper care, these clots can cause serious health problems.

May-Thurner syndrome symptoms can build slowly or begin suddenly with a clot. They tend to affect one leg, most often the left leg^4,8.

If symptoms occur, they may include the following changes:

Long-term vein pressure can cause chronic venous insufficiency^1,3. This problem may involve pooled blood, swelling, darkened skin, and ulcers.

These signs are not unique to May-Thurner syndrome^1,9. Imaging helps find the cause and assess blood flow^1,4.

A DVT can slow or block blood flow through a deep vein^4,8. May-Thurner syndrome raises clot risk through slow flow and vein wall damage^2,3.

If a DVT develops, warning signs may include:

If these DVT signs appear, contact a clinician for an assessment. A clot can break free and travel to the lungs^4,7.

Call emergency services now if any of these warning signs occur:

May-Thurner syndrome results from an artery pressing a pelvic vein against the spine. Experts do not fully know why this compression happens⁴.

The condition is reported more often in women⁸. It is also more common among adults ages 20 to 50⁴.

Several factors may raise clot risk when vein compression already exists^1,3:

These factors cannot confirm iliac vein compression syndrome^1,4. A diagnosis requires imaging of the affected veins^1,4.

Symptoms and a physical examination cannot confirm May-Thurner syndrome alone¹. Imaging is needed to assess clots, narrowing, blood flow, and nearby structures^1,3.

A clinician will ask about your symptoms and health history⁴. The examination may look for swelling, warmth, tenderness, skin changes, or enlarged veins^4,6.

A clotting workup can identify other DVT risks, especially in younger patients¹. MR venography is an alternative imaging method for diagnosing May-Thurner syndrome³.

The next test depends on the symptoms and suspected clot location. Testing often begins with an ultrasound when DVT is possible^1,3.

Duplex ultrasound uses sound waves to create images of veins and blood flow⁴. It is widely used as a first test for leg DVT^1,3.

The scan can assess many deep veins within the affected leg¹. Chronic DVT can cause varicose veins and other signs of chronic venous insufficiency³.

However, pelvic veins can be hard to see with ultrasound^1,3. The left common iliac vein can be compressed against the spine by the right common iliac artery¹.

Body shape and bowel contents may also limit the view³. A negative leg ultrasound may not exclude pelvic vein compression^1,9.

If suspicion remains high, imaging of the pelvis may be needed⁴. CT or MR imaging can show iliac vein compression^3,4.

CT venography uses X-rays and contrast dye to show veins^3,4. It can reveal compression, clots, and changes in pelvic anatomy³.

CT can also show other causes of pressure on a vein³. These may include enlarged lymph nodes, an abdominal mass, or bone changes³.

Dehydration is a reported risk factor for May-Thurner syndrome, and CT can show iliac vein compression³. Clinicians may see flattening of the left iliac vein on CT images³.

MR venography uses magnets and radio waves to show blood vessels^4,8. It can provide another view of iliac vein compression³.

However, the amount of vein compression may change over time^3,9. A single MR scan may not show the full pattern^3,9.

Access and cost can also limit the use of MR venography³. The care team may use ultrasound, CT, MRI, or venography to evaluate blood vessels^3,4.

Contrast venography uses injected dye and X-rays to show blood flow through veins⁴. A catheter may deliver the dye into the vein⁴.

Intravascular ultrasound, or IVUS, uses a small probe inside the blood vessel⁴. It provides detailed measurements of the vein and its wall^3,9.

Venography with IVUS can give a detailed view of the narrowed area³. Some sources describe it as the key test for confirming the condition^3,5.

Clinicians may use these catheter tests to confirm findings or clarify uncertain cases before planning treatment^3,5. IVUS may also help with placement of an iliac vein stent⁷.

Treatment depends on symptoms, blood flow, clotting, and imaging findings^1,5. The goals include restoring flow and lowering clot-related risks.

People without symptoms or major flow problems may not need a procedure^1,9. A clinician may watch for symptoms or clot-related problems instead⁹.

Mild symptoms may sometimes be treated with compression stockings⁷. These tight garments may reduce swelling and support lower-leg blood flow⁷.

New or worsening symptoms still need medical assessment^4,6. One-sided swelling, warmth, pain, or skin changes may suggest DVT^4,6.

Anticoagulants are medicines that reduce the blood’s ability to clot^6,7. They can prevent new clots and stop an existing clot from growing⁷.

People taking these medicines need monitoring for treatment problems. The care team chooses a plan based on each person’s situation.

Extensive DVT may need catheter treatment before the narrowed vein is treated^1,9. These methods may dissolve, break apart, or remove the clot^2,6,9.

Possible treatments for a large clot may include:

Clot-dissolving treatment may take several hours or days^6,7. Removing a clot with a device can avoid the medications used in thrombolysis, which have risks⁹.

Angioplasty uses a small balloon to widen the compressed vein^4,6. A clinician guides the balloon through a catheter to the narrowed area^4,6.

The balloon expands and stretches the vein open^4,6. This process can improve blood flow through the treated area.

An iliac vein stent is a small mesh tube placed inside the vein. It supports the treated section after the balloon is removed.

For a fixed blockage with symptoms, stenting can improve blood flow. It may also ease symptoms caused by the blocked vein.

If DVT is present, the clot may be removed before stent placement. The stent then holds the compressed part of the vein open.

Doctors first favor care without open surgery³. They may use surgery if that care does not work³.

Bypass surgery creates a new path around the compressed vein^4,8. Another operation moves the artery away from the vein^4,7.

A surgeon may also place tissue between the artery and vein^4,7. The added tissue forms a cushion between the blood vessels⁷.

An inferior vena cava filter sits inside a large vein in the abdomen^6,8. It can catch traveling clots before they reach the lungs^6,8.

The filter does not stop new clots from forming^6,7. It may be considered when anticoagulants cannot be used³.

Some people with ongoing clots during anticoagulant treatment may receive a filter. However, these filters are not used for every patient.

Recovery varies with the condition and treatment received⁹. Catheter procedures are less invasive than open clot surgery⁹.

The care team should provide instructions for treatment and recovery. Follow those instructions and ask questions if any step is unclear.

Anticoagulant treatment requires close monitoring for possible problems. Make sure you know who will manage each medicine.

May-Thurner syndrome may be associated with both DVT and post-thrombotic syndrome^1,6. This condition may cause lasting swelling, skin changes, high vein pressure, and ulcers.

Clot-related problems may recur in some cases³. A pulmonary embolism can also occur if a clot reaches the lungs⁴.

An iliac vein stent stays inside the treated vein. Your specialist can explain what follow-up is planned.

Helpful questions for your vascular specialist may include:

Reported treatment outcomes are generally good. Early DVT detection can improve access to effective care and symptom relief.

If one leg becomes swollen, painful, warm, tender, or discolored, contact a clinician. Also seek care for enlarged veins, recurring varicose veins, or leg ulcers.

If symptoms continue after a negative ultrasound, ask about pelvic imaging. Ultrasound may not clearly show the common iliac vein^1,3.

May-Thurner syndrome symptoms, diagnosis and treatment depend on blood flow and clots. Many people with iliac vein compression never need a procedure^1,9.