What is May-Thurner Syndrome?

May-Thurner syndrome is a condition where a vein in your pelvis, specifically the iliac vein, gets compressed by an overlying artery, which interferes with blood flow and can cause a vein narrowing or obstruction. This can sometimes go unnoticed, but common symptoms include pain, swelling, and changes in the skin of the affected leg. May-Thurner syndrome occurs in several forms, but the most common type is when the right artery presses down on the left vein. This syndrome can lead to blood clots, also known as deep venous thrombosis (DVT), and it should be considered in anyone who presents with a DVT in the iliac or femoral veins (veins in your pelvis or thigh).

Italian scientist Rudolf Virchow first identified this condition, in 1851, during a study of bodies who had experienced left-side iliofemoral thrombosis, which is a clot in the pelvis and thigh region. It wasn’t until 1957 that May and Thurner provided a more detailed description, including the discovery of fibrous bands within the veins that were being compressed by the artery. This specific condition was then named the May-Thurner syndrome after them.

Several studies have found that this condition is fairly common, with some even suggesting that it is a normal body variation. Symptoms arise from the pressure caused by the artery pressing against the vein. Blood flow gets restricted, which can cause injury to the vein and may even lead to thrombotic vascular occlusion, which is a fancy term for the formation of a clot that blocks the blood vessel. When this condition does occur, it most commonly appears in young women, especially after periods of inactivity, following surgery, or during or immediately after childbirth.

Not every person with May-Thurner syndrome will get DVT, but when DVT is found in the iliac or femoral veins, about two-thirds of the cases are found to have the characteristic vein compression of May-Thurner syndrome. DVT can happen suddenly and the clot often moves down into the veins of the leg, which can greatly increase the risk of a clot-related problem. In some cases, a clot can break off and travel to the lungs, leading to a serious condition called pulmonary embolism.

For those who do have symptoms, the goal of treatment for May-Thurner syndrome is to restore proper blood flow, relieve the pressure caused by the narrowed veins, and minimize the chances of developing postthrombotic syndrome, which is a long-term complication of DVT involving chronic leg swelling and pain. Generally, treatment will include blood thinners or other procedures to help dissolve the clot and then the placement of a special mesh tube, called a stent, to keep the vein open. This approach is used because of the syndrome’s persistent and fibrous nature.

What Causes May-Thurner Syndrome?

May-Thurner syndrome is a medical condition caused by a blockage in one of the major veins in the lower part of your body. This blockage is often the result of one large vein being squashed against your spine by a nearby artery. This usually happens with the left vein that’s next to your spine getting pressed on by the right artery. However, it can sometimes happen on the right side or involve a different vein entirely.

The artery which is pressing against the vein pulsates, or ‘beats’, and this causes wear and tear, altering the vein’s lining. This eventually leads to the formation of non-elastic, fibrous bands or growths. Over time, these bands cause the vein to narrow, making it harder for blood to flow back up to the heart. This can sometimes lead to a deep vein thrombosis (DVT), which is a blood clot in a deep vein.

Earlier research indicated that once these fibrous bands form and the vein narrows, it doesn’t go back to its original wide shape. Even after treating a blood clot, and making the blood flow better through a combination of medication, physical treatments, and surgery, the vein doesn’t widen again. Therefore, the main treatment for May-Thurner Syndrome is usually a procedure known as venous stenting, this involves putting a small metal mesh tube, or a ‘stent’, into the narrowed vein to hold it open and allow better blood flow.

Risk Factors and Frequency for May-Thurner Syndrome

May-Thurner syndrome is a condition that is believed to be underdiagnosed because many patients don’t show symptoms. Some people who have this syndrome may experience pain and swelling in the lower part of their body. This happens because this syndrome can cause veins to form in unusual ways. When this condition has been present for a while, it often leads to a condition called deep vein thrombosis (DVT) in the affected leg, especially the left one. This evidence was discovered in imaging studies which found signs of May-Thurner Syndrome in 22% to 76% of patients who had a DVT in the left leg.

May-Thurner syndrome is twice as common in women as in men.
Women with this syndrome are often between 30 and 50 years old and may also have a condition called pulmonary embolism.
Men with May-Thurner syndrome usually suffer from pain and edema (swelling caused by fluid) in the lower body.

Signs and Symptoms of May-Thurner Syndrome

May-Thurner syndrome is a medical condition that can present differently in different individuals. Some people might gradually develop symptoms of venous insufficiency, while others might experience sudden lower limb pain and swelling. The most frequently reported scenario is a younger woman experiencing swelling in the left lower leg, which gets better with rest and elevation. These symptoms could progress slowly to skin discoloration and ulcers. After a surgery, during or post-pregnancy, or upon starting oral contraceptives, some people might find their left lower limb swollen and painful. Rarely, both men and women can develop serious conditions like phlegmasia cerulea dolens.

The symptoms of May-Thurner syndrome can be subtle and go unnoticed due to the body’s ability to develop alternate blood flow routes. These symptoms could include a feeling of tightness in the left lower leg that disappears during sleep, slight swelling, skin discoloration, small, broken blood vessels on the skin’s surface or venous ulcers. However, these symptoms are not exclusive to May-Thurner syndrome. Conversely, these signs might suddenly appear after an unsuccessful vein treatment. Another common symptom associated with this condition is venous claudication, or leg pain induced by exercise.

May-Thurner syndrome progresses in three stages:

Stage I: asymptomatic compression of the left iliac vein
Stage II: formation of venous spurs
Stage III: left lower leg deep vein thrombosis (DVT).

A conclusive diagnosis of May-Thurner syndrome involves a holistic physical examination and imaging tests. The physical examination should cover complete vital signs, a detailed heart and lung examination, and an evaluation of both lower limbs.

Testing for May-Thurner Syndrome

If your doctor suspects a blockage in your blood vessels, they may use a Doppler ultrasound as the first imaging method. This technique can identify problems like weak blood flow or a clot in the veins. If the ultrasound doesn’t find a clot in the smaller veins, then the doctors will check the larger iliac and caval vessels. However, if the ultrasound doesn’t give clear views of these larger vessels, then other methods like a CT scan or an MR venogram may be recommended.

Doppler ultrasound is a convenient, non-surgical approach and is widely available in most medical facilities. However, its effectiveness largely depends on the operator’s skills. Although it has many uses, like mapping blood flow, measuring the extent of backward flow of blood, checking the width of a vessel, and looking for narrowing or blockages, using it to assess the inferior vena cava (the body’s largest vein) and iliac veins may be limited, especially in larger individuals or if other body structures get in the way.

CT venography, another imaging technique, is highly effective in identifying iliac vein compression. It can also provide clear images of narrowing veins, collateral veins, and blood clots. Aside from this, CT venography can rule out other causes of vein compression like enlarged lymph nodes, cancer, or internal bleeding. But it does have limitations. CT venography can sometimes overestimate the degree of vein compression in a dehydrated patient, leading to false indications of May-Thurner syndrome. It’s also not recommended for pregnant individuals and should be used with caution for those with kidney issues.

MR venography is a similar technique to CT venography but provides better and more detailed imaging of the structures. It’s also safe to use during pregnancy. However, its ability to diagnose May-Thurner syndrome might not be sufficient, given that the compression of the common iliac vein can sometimes be intermittent and variable. It’s also more expensive and not readily available like Doppler ultrasound or CT venography.

If non-invasive diagnostic procedures are ambiguous, doctors may utilize intravascular ultrasound, which has largely replaced the traditional catheter venography tests. Intravascular ultrasound avoids exposure to contrast agents, radiation, long procedure times, and bleeding risks associated with catheter venography. This technique is highly sensitive to vein compression and can offer precise data about the location and severity of fibrosis, narrowing veins, and clots. It’s often used when preparing to place a stent, visualizing guidewires during recanalization, and confirming stent placement. Further, it can detect early changes in the blood vessels.

Despite its strengths, intravascular ultrasonography does have shortcomings. It can’t provide information about surrounding anatomical structures, and it requires a minor invasive procedure. Also, it’s not widely available and may prove more challenging to apply than the other imaging methods already mentioned.

Treatment Options for May-Thurner Syndrome

May-Thurner syndrome is a condition where there’s pressure on one of your main leg veins which can make it harder for blood to flow properly. The treatment for this condition varies depending on the severity of the symptoms and if there’s a blood clot present.

If you have May-Thurner syndrome but don’t have a blood clot, you might get treatments like physical therapies – like wearing compression stockings and elevating your leg – to help improve blood flow. Additionally, your doctor will talk to you about factors that could increase your risk of developing blood clots, and you’ll likely need regular check-ups.

If you have May-Thurner Syndrome and a blood clot, you’ll probably be given medication to prevent the clot from getting bigger and to help the body break it down. In some cases, waiting to start these medications can lead to serious complications such as harmful blockages in your lungs.

Often, the initial treatment will be a common blood thinner called heparin. This may then be followed by other types of blood thinners, such as fondaparinux, warfarin or newer alternatives. One study found that a medication called rivaroxaban was safe and had a lower risk of causing excessive bleeding compared to warfarin.

However, using blood thinners alone may not be enough for patients who have blood clots as a result of May-Thurner syndrome. In these cases, it might be necessary to directly target these clots with procedures that involve a thin tube, or catheter—this approach is often followed by the insertion of a stent, a device which is used to keep veins open and prevent future blockages.

It’s important to mention that certain individuals may not be suitable for these procedures due to factors such as recent surgeries, underlying conditions, or planned procedures. For example, someone who’s had head trauma in the last three months or a person with severe high blood pressure may not be suitable candidates.

In rarely situations, when other treatments are not effective or suitable, the affected segment of the vein might need to be surgically removed. Some possible surgical options include various types of bypass surgeries which reroute blood flow to reduce pressure on the affected vein.

Compression of the iliac vein, a major vein in your lower body, can occur due to various medical issues such as cancer, lymph node enlargement, blood clot (hematoma), or skin infection (cellulitis). Other possible causes might be certain diseases or anatomical variations like uterine leiomyoma (a type of tumor in the uterus), aortoiliac aneurysm (an enlargement of the main blood vessel that supplies blood to the abdomen, pelvis, and legs), retroperitoneal fibrosis (a disorder where fibrous tissue develops in the back of your abdomen), or osteophytes (bone spurs).

If someone comes in with an unexplained blood clot in the iliofemoral vein (a vein in the thigh), doctors should conduct tests for blood clotting disorders and cancer.

What to expect with May-Thurner Syndrome

May-Thurner syndrome often doesn’t show any symptoms in most people. Studies on cadavers (dead bodies used for medical research) have shown that this syndrome is more common than what is reported by patients showing symptoms. If identified on time and the physical pressure on the affected area is relieved, most May-Thurner syndrome patients can lead a high-quality life.

It’s crucial to keep monitoring the situation periodically to spot any worsening of symptoms. Regular check-ups are also advised to prevent the return of blood clots and to ensure a good quality of life.

Possible Complications When Diagnosed with May-Thurner Syndrome

Postthrombotic syndrome is a frequent side-effect of May-Thurner syndrome. If properly treated, this syndrome can be reduced to less than 10% of cases. This syndrome affects people who have deep vein thrombosis (DVT – a blood clot deep in your veins), regardless of its cause. Symptoms of this condition include chronic pain, swelling, and sores on the affected limb.

Risk Factors:

Large blood clot
Remaining blood clot after treatment
Obesity
Recurring blood clot

A study by Comerota and colleagues shows that remaining blood clot after a catheter-based treatment has a direct relationship with the likelihood of developing postthrombotic syndrome. Treatments like mechanical or medicine-based clot breakdown can lower the risk of developing this syndrome. Moreover, patients can also benefit from wearing knee- or thigh-high compression stockings and having a regular prescribed exercise regimen.

Preventing May-Thurner Syndrome

People who have May-Thurner syndrome should be educated about the signs and symptoms of blood clots. It’s important to pay attention to these signals and promptly seek medical care as soon as these symptoms show up. Regular check-ups are advised to monitor any increase in these symptoms. It’s beneficial for individuals with this condition to use compression and to elevate the affected limb to promote blood flow.

Furthermore, those receiving blood thinning treatment need to be informed about potential risks of excessive bleeding. They should be taught to recognize this serious condition and ensure immediate medical attention if they experience uncontrolled or extensive bleeding.

Frequently asked questions

May-Thurner syndrome is a condition where the iliac vein in the pelvis gets compressed by an overlying artery, leading to vein narrowing or obstruction. This can cause symptoms such as pain, swelling, and changes in the skin of the affected leg. It can also lead to blood clots, known as deep venous thrombosis (DVT).

May-Thurner syndrome is twice as common in women as in men.

Signs and symptoms of May-Thurner Syndrome can vary among individuals, but some common signs and symptoms include: - Gradual development of symptoms of venous insufficiency - Sudden lower limb pain and swelling - Swelling in the left lower leg, which improves with rest and elevation (most frequently reported scenario, especially in younger women) - Slow progression to skin discoloration and ulcers - Swelling and pain in the left lower limb after surgery, during or post-pregnancy, or upon starting oral contraceptives - Rarely, development of serious conditions like phlegmasia cerulea dolens in both men and women Other symptoms that may be associated with May-Thurner Syndrome include: - Feeling of tightness in the left lower leg that disappears during sleep - Slight swelling - Skin discoloration - Small, broken blood vessels on the skin's surface - Venous ulcers - Venous claudication, which is leg pain induced by exercise It is important to note that these symptoms are not exclusive to May-Thurner Syndrome and can also occur after an unsuccessful vein treatment.

May-Thurner Syndrome is caused by a blockage in one of the major veins in the lower part of the body, often due to one large vein being squashed against the spine by a nearby artery.

The doctor needs to rule out the following conditions when diagnosing May-Thurner Syndrome: 1. Cancer 2. Lymph node enlargement 3. Blood clot (hematoma) 4. Skin infection (cellulitis) 5. Uterine leiomyoma (a type of tumor in the uterus) 6. Aortoiliac aneurysm (an enlargement of the main blood vessel that supplies blood to the abdomen, pelvis, and legs) 7. Retroperitoneal fibrosis (a disorder where fibrous tissue develops in the back of your abdomen) 8. Osteophytes (bone spurs)

The types of tests that may be ordered to diagnose May-Thurner Syndrome include: 1. Doppler ultrasound: This is the first imaging method used to identify problems like weak blood flow or a clot in the veins. It can be limited in assessing the inferior vena cava and iliac veins in larger individuals or if other body structures obstruct the view. 2. CT venography: This imaging technique is highly effective in identifying iliac vein compression and can provide clear images of narrowing veins, collateral veins, and blood clots. It can also rule out other causes of vein compression. However, it has limitations and should be used with caution in certain individuals. 3. MR venography: Similar to CT venography, MR venography provides better and more detailed imaging of the structures. It is safe to use during pregnancy but may not be sufficient to diagnose May-Thurner Syndrome in cases where the compression of the common iliac vein is intermittent and variable. 4. Intravascular ultrasound: This technique is highly sensitive to vein compression and can offer precise data about the location and severity of fibrosis, narrowing veins, and clots. It is often used when preparing to place a stent and can detect early changes in the blood vessels. However, it requires a minor invasive procedure and is not widely available.

The treatment for May-Thurner Syndrome varies depending on the severity of the symptoms and the presence of a blood clot. If there is no blood clot, treatments like physical therapies, wearing compression stockings, and elevating the leg may be recommended to improve blood flow. Regular check-ups and discussions about factors that increase the risk of blood clots are also important. If there is a blood clot, medication may be given to prevent the clot from getting bigger and help the body break it down. Blood thinners like heparin, fondaparinux, warfarin, or newer alternatives may be used. In some cases, procedures involving a catheter and stent insertion may be necessary to directly target the clots and prevent future blockages. Surgical removal of the affected vein may be considered in rare situations when other treatments are not effective or suitable.

The side effects when treating May-Thurner Syndrome can include: - Chronic pain - Swelling - Sores on the affected limb - Postthrombotic syndrome, which can occur as a frequent side effect of May-Thurner Syndrome and can be reduced to less than 10% of cases if properly treated. Postthrombotic syndrome affects people who have deep vein thrombosis (DVT), regardless of its cause.

The prognosis for May-Thurner Syndrome is generally good if it is identified and treated in a timely manner. Treatment aims to restore proper blood flow, relieve pressure on the narrowed veins, and minimize the risk of complications such as postthrombotic syndrome. With appropriate treatment, most patients with May-Thurner Syndrome can lead a high-quality life. Regular monitoring and check-ups are important to prevent the return of blood clots and ensure a good quality of life.

A vascular specialist or a vascular surgeon.

Anticoagulation Deep Vein Thrombosis Health