May-Thurner syndrome is a condition in which a vein in the pelvis becomes compressed by a nearby artery and the spine. In the most common form, the right common iliac artery presses the left common iliac vein against the lower spine, which can make it harder for blood to flow out of the left leg.
Some people have this type of vein compression without any symptoms. When the compression becomes clinically significant, May-Thurner syndrome can cause swelling, heaviness or pain in one leg and may increase the risk of deep vein thrombosis (DVT), which is a blood clot in a deep vein.
Diagnosis may involve ultrasound, CT venography, MR venography, conventional venography or intravascular ultrasound (IVUS). Treatment depends on whether symptoms, a significant blockage or a blood clot are present and may include conservative care, blood-thinning medication, clot removal or placement of a venous stent.
Main symptoms
May-Thurner syndrome does not always cause symptoms, and anatomical compression of the iliac vein can be found in people without clinically significant disease. When symptoms occur, they usually affect one leg, most commonly the left leg.
The main symptoms may include:
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Swelling in one leg
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Leg pain
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A feeling of heaviness in the affected leg
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Varicose veins
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Changes in the skin
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Venous ulcers
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Signs and symptoms related to deep vein thrombosis (DVT)
Symptoms develop when compression interferes enough with venous blood flow to cause venous hypertension, obstruction or clot formation.
Common causes
May-Thurner syndrome is caused by anatomical compression of a pelvic vein. In its classic form, the right common iliac artery crosses over and compresses the left common iliac vein against the spine.
The repeated pulsation of the artery against the compressed vein may also contribute to injury inside the vein over time. This can further restrict blood flow and may create conditions that favor the development of a blood clot.
Other anatomical variations of May-Thurner syndrome can also occur. In addition, circumstances that increase the general risk of blood clot formation, such as pregnancy or the postpartum period, immobility, trauma and surgery, may make a pre-existing compression more clinically important.
May-Thurner syndrome is not an infection and is not transmitted from one person to another. It is not contagious or sexually transmitted and cannot be spread through casual contact.
Confirming a diagnosis
Diagnosis of May-Thurner syndrome is based on symptoms together with imaging that shows compression or narrowing of the iliac vein. An ultrasound is commonly used when DVT is suspected, although the veins deep within the pelvis can be difficult to evaluate fully with this test.
CT venography or MR venography may provide a clearer view of the pelvic veins and help identify the location and extent of compression. Doctors also consider whether the anatomical narrowing is actually associated with symptoms, obstruction or thrombosis because iliac vein compression can exist without causing disease.
When a procedure is being considered, catheter venography and intravascular ultrasound, or IVUS, may be used to examine the vein more closely. IVUS allows the inside of the blood vessel to be assessed and can help define the severity and location of the narrowed area before treatment.
Treatment options
Treatment for May-Thurner syndrome depends on the presence and severity of symptoms, whether blood flow is significantly obstructed and whether DVT has developed. Not every person with iliac vein compression needs treatment because the anatomical pattern can occur without symptoms.
1. Conservative treatment
Conservative management may be considered in selected people without severe obstruction or complications. Compression therapy may be used in some patients to help control symptoms related to venous insufficiency, although it does not correct the underlying anatomical compression.
2. Anticoagulant medication
When May-Thurner syndrome is associated with DVT, anticoagulants, also known as blood thinners, may be prescribed to reduce the risk of the existing clot becoming larger and to help prevent additional clots. The appropriate medication and duration of treatment depend on the individual clinical situation.
Anticoagulant treatment may also be used after venous stent placement. However, research has not established one ideal antithrombotic regimen or treatment duration for every patient after stenting for May-Thurner syndrome.
3. Clot removal
People with acute iliofemoral DVT may undergo procedures designed to remove the blood clot in selected cases. These procedures may be combined with treatment of the underlying iliac vein obstruction when clinically appropriate.
Evidence suggests that adding venous stenting after clot removal can help maintain blood flow in appropriately selected patients with May-Thurner syndrome. However, these procedures also carry potential complications and should be considered according to the severity of the condition and the individual patient's risks.
4. Venous stent
A venous stent is a small device placed inside the compressed vein to help keep it open and improve blood flow. Stenting may be considered when May-Thurner syndrome causes clinically significant iliac vein obstruction, particularly when symptoms or DVT are present.
Venography and IVUS may be used during treatment to determine the extent of narrowing and guide stent placement. Follow-up is important after the procedure because the stent can become narrowed or blocked and recurrent DVT can occur.
May-Thurner syndrome during pregnancy
Pregnancy and the postpartum period increase the general risk of venous blood clots and may make an existing iliac vein compression more clinically significant. Management of May-Thurner syndrome during pregnancy therefore requires consideration of both the anatomical obstruction and the increased risk of thrombosis.
Treatment may involve anticoagulation and multidisciplinary care depending on symptoms, previous blood clots and other risk factors. Management should be individualized because the evidence available for May-Thurner syndrome during pregnancy remains limited.