17213 May Thurner Syndrome
Informed by recognized medical guidance
Overview
May Thurner syndrome is a condition in which a major artery in the pelvis presses on the main vein that drains blood from your left leg. This pressure can narrow the vein and make it harder for blood to flow back to your heart, which raises the risk of blood clots in the left leg.
Key facts
- It can make the left leg swell, feel heavy, or ache.
- Many people have the same vein anatomy but never have symptoms.
- It is more common in women, especially between the ages of 20 and 40.
- The biggest worry is developing a blood clot in the leg, called deep vein thrombosis (DVT).
- Treatment works well to improve blood flow and reduce clot risk.
May Thurner syndrome itself is not commonly diagnosed. However, the anatomical pattern that causes it may be present in about one in four people, yet only a small number of them ever develop symptoms or a blood clot.
It most often affects women, particularly after pregnancy or in their 20s to 40s. That said, it can happen to men and women of any age, especially if they have other risk factors for blood clots.
Symptoms
- Sudden, severe swelling and severe pain in your left leg
- Chest pain or trouble breathing, which can mean a blood clot has traveled to your lungs
- Coughing up blood or feeling lightheaded with fast breathing
- ⚠New or worsening leg swelling and pain that does not go away
- ⚠Leg feels very warm, red, or tender
- ⚠Difficulty walking or bearing weight on the leg
Common symptoms
- Swelling in the left leg, ankle, or foot with no obvious cause
- Aching, heaviness, or tiredness in the left leg
- Visible veins, such as varicose veins on the thigh or calf
- A feeling of warmth or redness in the leg
- Leg cramps or discomfort after standing for long periods
Symptoms in children
- Leg swelling or a noticeable difference in leg size
- Limping or complaining of leg pain
- Unexplained redness or warmth in one leg
Symptoms in older adults
- Similar symptoms of one-sided leg swelling and discomfort
- Symptoms may be mistaken for normal aging, arthritis, or other circulation problems
- Skin changes on the lower leg, such as darkening or hardening, may develop
Causes
Main causes
- A person is born with the right iliac artery crossing the left iliac vein in a way that can press on it.
- The pressure can irritate the vein wall and slow blood flow.
- Over time, the narrowed vein can become damaged, making blood clots more likely.
Risk factors
- Being female
- Recent pregnancy or childbirth
- Long periods of immobility, such as bed rest or a long flight
- Conditions that make blood clot more easily
- Previous blood clots or a family history of clots
When to see a doctor
See a doctor urgently if:
- Sudden, severe swelling and pain in your left leg
- Shortness of breath, chest pain, or coughing up blood
Book a routine appointment if:
- Ongoing swelling or heaviness in one leg
- Varicose veins that appear suddenly or cause discomfort
- Any leg symptom that worries you
Diagnosis
A doctor will ask about your symptoms, check your legs, and review your medical history. They may look for differences in leg size, swelling, and visible veins. If they suspect May Thurner syndrome or a blood clot, they will order imaging tests to see how blood is flowing in your veins.
Tests that may be done
- Ultrasound – uses sound waves to check blood flow and look for clots
- Venogram – an X-ray test that uses dye to show your veins
- CT scan or MRI – detailed images of the pelvic blood vessels
- Blood tests – check for clotting problems or signs of a clot
What to expect at your appointment
If your doctor suspects May Thurner syndrome, you will likely be referred to a specialist in blood vessel conditions, called a vascular specialist. The tests are usually painless and non-invasive, though a venogram may involve a small needle. Your doctor will explain each step and answer any questions.
Treatment
Treatment focuses on relieving symptoms, preventing blood clots, and keeping blood moving normally. If you do not have symptoms, you may not need any treatment. If a blood clot has already developed, treatment usually starts right away.
Self-care at home
- Wear compression stockings if your doctor recommends them
- Raise your leg when sitting or lying down to help reduce swelling
- Move your legs regularly and avoid sitting or standing for long periods
- Stay well hydrated, especially on long trips
Medical treatments
Doctors often prescribe blood thinners, also called anticoagulants, to prevent or treat blood clots. These medicines do not dissolve an existing clot right away, but they stop it from growing and help your body break it down over time. In some cases, a specialist may recommend a minimally invasive procedure to open the narrowed vein. This can involve inserting a small tube, inflating a tiny balloon to widen the vein, and placing a stent (a small mesh tube) to keep it open. Sometimes clot-busting medicine can be delivered directly to the area through this tube. The exact approach depends on your situation and is decided by your healthcare team.
When is surgery considered?
Surgery is rarely needed, but it may be considered if other treatments do not relieve symptoms or if the vein is severely blocked. Operations can involve moving the artery or vein, or creating a bypass to reroute blood flow around the compressed area.
Living with this condition
Most people with May Thurner syndrome can live a full and active life. It helps to wear compression stockings as advised, take note of leg swelling, and stay alert to any new or unusual symptoms. Your doctor will tell you if you need long-term blood thinners and how often to have follow-up checkups.
Lifestyle tips
- Exercise regularly to keep blood flowing
- Take short walks during long flights or car rides
- Avoid sitting with your legs crossed for long periods
- Keep a healthy weight to reduce pressure on your veins
- Stop smoking, if you smoke
Diet and exercise
A balanced diet low in extra salt can help reduce leg swelling. Gentle exercises like walking, swimming, or cycling can improve circulation and strengthen your legs. Always check with your healthcare provider before starting a new exercise routine, especially if you have a blood clot.
Mental health and emotional wellbeing
Dealing with a condition that can cause swelling, pain, or fear of blood clots may feel stressful. It is normal to feel worried sometimes. Talking openly with your doctor, getting support from family and friends, and staying informed can help you feel more in control.
Prevention
You cannot prevent the anatomical structure that causes May Thurner syndrome, because you are born with it. However, you can take steps to reduce your chance of developing blood clots, especially if you have other risk factors.
Complications
If left untreated
- Deep vein thrombosis (DVT) – a blood clot in the deep vein of your leg
- Post-thrombotic syndrome – long-lasting leg pain, swelling, and skin changes after a clot
- Pulmonary embolism – a blood clot that travels to the lungs, which is an emergency
Long-term outlook
With proper treatment, the outlook is very good. Most people feel better and can return to their normal activities. Even if a blood clot has occurred, quick treatment greatly lowers the risk of serious problems. Working closely with your healthcare provider helps you stay as healthy as possible.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 31, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.