May-Thurner Syndrome

May-Thurner Syndrome is a vascular condition in which the left iliac vein in the pelvis is compressed, most often by the right iliac artery, reducing blood flow from the left leg back to the heart. It may cause left leg swelling, pain, heaviness, varicose veins or deep vein thrombosis, and it is assessed and treated by vascular specialists.

Overview

May-Thurner Syndrome is a condition in which the left common iliac vein, a major vein that carries blood out of the left leg and pelvis, is narrowed or compressed. The compression usually occurs where the right common iliac artery crosses over the vein and presses it against the spine. Because the vein is partly squeezed, blood may drain more slowly from the left leg.

The condition is also known as iliac vein compression syndrome or Cockett syndrome. Many people have some degree of iliac vein compression without knowing it. May-Thurner Syndrome becomes clinically important when the narrowing causes symptoms or contributes to a deep vein thrombosis, which is a blood clot in a deep vein.

Reduced venous outflow can lead to pressure in the leg veins. Over time, this may cause swelling, discomfort, varicose veins, skin discoloration or, in more advanced cases, venous ulcers. In other people, the first sign may be a clot in the left leg, especially if other clotting risk factors are also present.

Symptoms

May-Thurner Syndrome symptoms vary widely. Some people have no symptoms and the condition is found incidentally during imaging for another reason. Others notice symptoms that are worse after standing for a long time, sitting for long periods, exercising, travelling or during pregnancy.

Common symptoms are usually on the left side and may include:

• Left leg swelling, especially in the calf, ankle or entire leg
• Aching, heaviness, tightness or a feeling of fullness in the leg
• Visible varicose veins or new prominent veins around the groin, thigh or lower abdomen
• Skin discoloration, itching, dryness or thickening caused by chronic venous pressure
• Leg fatigue or discomfort that improves with elevation
• Pelvic or lower abdominal discomfort in some patients

If a deep vein thrombosis develops, symptoms can be more sudden. The leg may become swollen, painful, warm, red or tender. A clot can sometimes travel to the lungs and cause a pulmonary embolism, which may present with shortness of breath, chest pain, coughing blood, faintness or a rapid heartbeat. These symptoms require urgent medical attention.

Causes & Risk Factors

The main cause of May-Thurner Syndrome is an anatomical relationship between the pelvic artery, pelvic vein and spine. The right iliac artery passes over the left iliac vein, and its pulsation can gradually irritate or compress the vein. In some people, this leads to narrowing and internal scarring of the vein wall, which can slow blood flow and increase the chance of clot formation.

This anatomical compression is often present for years before it causes symptoms. Not every person with iliac vein compression develops a clot or needs treatment. Symptoms are more likely when the narrowing is significant or when another factor increases pressure in the veins or raises the risk of thrombosis.

Risk factors that can make May-Thurner Syndrome more likely to become symptomatic include pregnancy and the postpartum period, use of estrogen-containing hormone therapy or contraception, prolonged immobility, recent surgery, long-distance travel, dehydration, inherited or acquired clotting tendencies, active cancer, major injury and a previous history of deep vein thrombosis. The condition is often discussed in relation to left-sided leg clots because the left iliac vein is most commonly affected.

Diagnosis

Diagnosis starts with a medical history and physical examination. A doctor asks about leg swelling, pain, previous blood clots, pregnancy, medicines, surgeries, travel, family history of thrombosis and other risk factors. The examination looks for differences in leg size, tenderness, skin changes, varicose veins and signs of chronic venous disease.

Duplex ultrasound is often the first test when a leg clot is suspected. It is non-invasive and useful for examining veins in the thigh and lower leg. However, it may not clearly show the pelvic veins, so a normal ultrasound does not always exclude May-Thurner Syndrome if symptoms strongly suggest iliac vein compression.

Additional imaging may include CT venography or MR venography, which can show the iliac veins, surrounding arteries and any clot or narrowing in the pelvis. In selected cases, catheter venography and intravascular ultrasound may be used by vascular specialists to measure the degree of narrowing from inside the vein and to plan endovascular treatment. Blood tests may also be considered to assess clotting risk, kidney function before contrast imaging or other medical causes of swelling.

Treatment Options

May-Thurner Syndrome treatment depends on symptoms, the severity of vein narrowing, whether a deep vein thrombosis is present, and the person’s overall health. The right approach is decided by a vascular specialist after assessment and appropriate imaging. People with mild symptoms and no clot may be managed conservatively, while those with significant obstruction or thrombosis may need more active treatment.

Conservative treatment may include graduated compression stockings, leg elevation, regular walking, avoidance of prolonged immobility and management of contributing factors. If a blood clot is present, anticoagulation medication is commonly used to reduce the risk of clot growth and recurrence. The exact medicine, duration and monitoring plan should be chosen by the treating doctor.

For extensive or recent clots, specialists may consider catheter-based procedures such as thrombolysis or thrombectomy to dissolve or remove clot from the affected vein. If significant iliac vein compression remains, balloon angioplasty and placement of a venous stent may be used to keep the vein open and improve blood flow. Stents require follow-up imaging and medication decisions tailored to the patient.

Surgery is less commonly needed because many cases can be treated with minimally invasive endovascular techniques. Treatment may also involve hematology input if there is an underlying clotting disorder, and obstetric or gynecologic input when symptoms occur around pregnancy or hormone therapy. Patients should not start or stop blood-thinning medicines without medical guidance.

Living With / Prognosis

Many people with May-Thurner Syndrome do well when the condition is recognized and managed appropriately. The outlook depends on whether a clot has occurred, how long symptoms have been present, the degree of venous damage and whether there are other clotting risks. Early evaluation is helpful because untreated venous obstruction may contribute to chronic swelling and post-thrombotic symptoms.

Daily habits can support venous circulation. Patients may be advised to walk regularly, maintain a healthy weight, elevate the leg when swollen, use prescribed compression stockings and take breaks from sitting during work or travel. If anticoagulation is prescribed, it is important to follow instructions carefully and tell healthcare professionals about the medication before procedures or new prescriptions.

Follow-up is an important part of care, especially after a clot or venous stent. Appointments may include symptom review, ultrasound or other imaging, and discussion of ongoing medication needs. Women who are pregnant, planning pregnancy or using hormonal therapy should discuss individualized risk management with their doctor.

Acibadem International’s multidisciplinary vascular specialists and JCI-accredited hospitals diagnose and treat May-Thurner Syndrome for international patients, coordinating imaging, endovascular care and follow-up when appropriate. As with all vascular conditions, care should be personalized after a specialist evaluation.

When to See a Doctor

A person should seek medical advice if they have persistent swelling, aching, heaviness or visible vein changes in one leg, especially if symptoms are mainly on the left side. Evaluation is also appropriate when swelling is recurrent, worsens after standing or sitting, or does not improve with simple measures such as rest and elevation.

Urgent medical care is needed for sudden leg swelling, new calf or thigh pain, warmth, redness or tenderness, because these can be signs of deep vein thrombosis. Emergency assessment is needed for chest pain, shortness of breath, coughing blood, fainting or a sudden rapid heartbeat, as these symptoms may indicate a pulmonary embolism.

People with a past history of blood clots, known clotting disorders, recent surgery, cancer, pregnancy, postpartum status or estrogen-containing medication should be especially cautious about new one-sided leg symptoms. A qualified doctor can decide which tests are needed and whether referral to vascular surgery, interventional radiology or hematology is appropriate.

Frequently asked questions

What is May-Thurner Syndrome?

May-Thurner Syndrome is compression of the left iliac vein in the pelvis, most often by the right iliac artery. This can slow blood flow from the left leg and may cause swelling, discomfort, chronic venous changes or deep vein thrombosis.

Is May-Thurner Syndrome dangerous?

Many people with iliac vein compression have no symptoms and may never need treatment. It becomes medically important when it causes significant symptoms or contributes to a deep vein thrombosis. Prompt assessment helps reduce the risk of complications and guides safe treatment.

Why does May-Thurner Syndrome usually affect the left leg?

The left common iliac vein passes under the right common iliac artery near the spine. In some people, the artery presses the vein against the spine and narrows it. This anatomical pattern is why symptoms and clots are more often left-sided.

How is May-Thurner Syndrome diagnosed?

Diagnosis usually begins with a history, physical examination and duplex ultrasound, especially if a clot is suspected. Because the compressed vein is in the pelvis, CT venography, MR venography, catheter venography or intravascular ultrasound may be needed to see the narrowing clearly.

Can May-Thurner Syndrome be treated without surgery?

Yes, some patients are managed with compression stockings, movement, leg elevation and monitoring, especially if symptoms are mild and there is no clot. If a clot is present, anticoagulation may be needed. More significant obstruction may require minimally invasive endovascular treatment, which is decided after specialist assessment.

What is an iliac vein stent?

An iliac vein stent is a small mesh tube placed inside a narrowed pelvic vein to help keep it open. It is usually inserted through a catheter by a vascular or interventional specialist. Follow-up imaging and medication decisions are important after stent placement.

When should someone seek urgent care for possible May-Thurner Syndrome complications?

Urgent care is needed for sudden one-sided leg swelling, new leg pain, warmth or redness, because these may suggest a deep vein thrombosis. Emergency care is needed for chest pain, shortness of breath, fainting, coughing blood or a sudden rapid heartbeat, which may suggest a pulmonary embolism.

References

• Society for Vascular Surgery
• American Venous Forum
• Cleveland Clinic
• National Heart, Lung, and Blood Institute
• European Society for Vascular Surgery

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.