Patient Education Blog

May-Thurner Syndrome


Some people have a narrowing of their big left pelvic vein (= left common iliac vein) that can put them at risk for a blood clot (deep vein thrombosis = DVT) in that area and in the left leg. The narrowing is due to pressure onto the vein by the overlying big pelvic artery (= right common iliac artery), shown on image 1 . This condition is called May Thurner syndrome. It is an anatomic variant people are born with, but it is not inherited from the parents. While May-Thurner syndrome causes DVT in some people, in many it causes no problems and is irrelevant.

Image 1: Anatomy of May-Thurner Syndrome (graphic design: Jeff Harrison, Wilmington, NC)


Normally, the blood that comes from the legs flows through the deep veins of the legs and the pelvis into the big vein in the abdomen (= inferior vena cava) and then to the heart (figure 1). Normal anatomy is that the artery that goes to the right leg (= right common iliac artery) lies on top of the vein coming from the left leg (= left common iliac vein), shown in image 1. This close proximity leads, in some people, to pressure of the artery onto the vein, so that the vein is pinched between the artery in front and the vertebral body behind it. This may lead to varying degrees of narrowing of the vein and is called “May Thurner syndrome”. It is not a disease, but a congenital anatomic variant. Mild and moderate degrees of narrowing are typically asymptomatic. More severe degrees can lead to an impairment of blood flow from the leg. The narrowed vein can also clot, resulting in left leg DVT.


The syndrome is named after the physicians R. May and J. Thurner, who first described this phenomenon in 1957. It has also been termed the “iliac compression syndrome”. It is likely the reason why more DVTs, particularly during pregnancy, occur in the left leg than in the right.

How common is it?

Some degree of narrowing of the iliac vein appears to be very common. However, this has not been studied well. A small radiologic study indicated that nearly 2/3rds of people have a mild narrowing, and half have nearly 50 % narrowing of the vein (reference 1). However, how common severe narrowing, i.e. more than 90 % narrowing is, is not known.


Many people with May-Thurner syndrome have no symptoms, even if they have pronounced narrowing of the iliac vein. This is because other, smaller veins that bypass the narrowed area enlarge and drain the blood from the leg vein very effectively. These bypassing veins are called “collaterals”. Some people with severe narrowing have leg swelling and pain, symptoms that are often called chronic venous insufficiency. And, finally, some people are at increased risk for DVT from the narrowing, particularly if other risk factors (such as pregnancy, contraceptives or clotting disorders) are also present.


A routine Doppler ultrasound of the legs that is typically done to evaluate for DVT can not discover May-Thurner, as the veins in the pelvis can typically not be well seen by a Doppler ultrasound – they are too far above the groin (above the “inguinal ligament”, in medical terms) and too deep to be optimally imaged. To make a diagnosis a CT venogram (CTV) or MR venogram (MRV) are needed, or an invasive contrast venogram study. Intravascular ultrasound (IVUS) has also come in use in recent years to detect May-Thurner syndrome (references 2,3).


(a) No treatment is needed or indicated if the narrowing is coincidentally discovered and is not causing any symptoms. (b) In the patient who has chronic leg swelling, pain or even a skin ulcer (i.e. symptoms of venous insufficiency or postthrombotic syndrome) and who is found to have May Thurner syndrome, stenting of the narrowed stretch of vein (image 2) can lead to significant symptom improvement. (c) It has not been studied and is not known whether stenting is beneficial (i.e. whether it reduces the future risk of another clot) in the patient who had a DVT or PE and is found to have May-Thurner syndrome, but has recovered from the DVT and has no leg symptoms.

Image 2: Stent (graphic design: Jeff Harrison, Wilmington, NC)

Since 1995 venous stents have been placed into the narrowed area of the veins, to widen them and keep them expanded (ref 4-9). Unfortunately, only few studies have investigated the long-term success of the procedure, i.e. how often the stents improve symptoms and remain patent. Stents appear beneficial at least in the short-term improvement of symptoms, within the first 1-2 years of stent placement (references 4-9). However, nearly 2/3rds of stents may close up within the first 5 years of their placement (ref 9). When that happens, repeat radiological procedures to re-open the stents can often be successfully performed. Thus, overall, nearly ¾ of all stents are open 5 years after their placement (ref 9). Unfortunately, it is not known (a) whether patients who had a stent placed should remain on long-term (life-long) blood thinners, such as warfarin (coumadin©), and (b) whether aspirin has any benefit in keeping these stents open if blood thinners like warfarin are not given.

In the past, surgical procedures were done to take the pressure off the vein by moving the overlying artery somewhere else: (a) venous bypass surgery of the narrowed area, (b) cutting of the iliac artery and repositioning of the artery behind the iliac vein, and (c) construction of a tissue sling or flap to lift the artery off the iliac vein. These surgeries are not commonly done any more, as stenting has become the main treatment.

Personal Comment

If a patient has a fair amount of leg pain and swelling and a localized narrowing in the left common iliac vein, i.e. May Turner syndrome, I typically recommend stent placement. Once a stent has been placed I recommend at least 3 months of warfarin, target INR 2.0-3.0. Thereafter, the decision to come off or stay on warfarin depends on the patient’s risk factors for recurrent clots (DVT), such as (a) what triggered the first clot, (b) how many episodes of DVT the patient has had previously, (c) whether the patient has a strong clotting disorder, (d) whether the patient has left-over clot in his/her legs, and (e) whether a D-dimer blood test is positive or negative. If a decision is made to discontinue the blood thinner (such as warfarin), then I typically recommend long-term aspirin 81 mg per day. However, it is not known whether aspirin has any benefit in keeping venous stents open.


  1. Kibbe MR et al. Iliac vein compression in an asymptomatic patient population. J Vasc Surg 2004;39:937-943.
  2. Murphy EH et al. Device and imaging-specific volumetric analysis of clot lysis after percutaneous mechanical thrombectomy for iliofemoral DVT. J Endovasc Therapy 2010;17:423-433.
  3. Raju S et al. High prevalence of nonthrombotic iliac vein lesions in chronic venous disease: a permissive role in pathogenicity. J Vasc Sug 2006;44:136-144.
  4. Berger A et al: Iliac compression syndrome treated with stent placement. J Vasc Surg 1995;21:510-514.
  5. Neglen P et al.: Balloon dilatation and stenting of chronic iliac vein obstruction: technical aspects and early clinical outcome. J Endovasc Ther 2000;7:79-91.
  6. O’Sullivan GJ et al.: Endovascular management of iliac vein compression (May-Thurner) syndrome. J Vasc Intervent Radiol 2000;11:823-836.
  7. AbuRahma AF et al.: Iliofemoral deep vein thrombosis: conventional therapy versus lysis and percutaneous transluminal angioplasty and stenting. Ann Surg 2001;233:752-760.
  8. Heijmen RH et al.: Endovascular stenting in May Thurner syndrome. J Cardiovasc Surg 2001;42:83-87.
  9. Kwak HS et al. Stents in common iliac vein obstruction with acute ipsilateral deep venous thrombosis: early and late results. J Vasc Interv Radiol. 2005;16:815-822.
  10. Knipp BS et al. Factors associated with outcome after interventional treatment of symptomatic iliac vein compression syndrome. J Vasc Surg 2007;46:743-749.

For health care professionals

This same topic, discussed for health care professionals, can be found here.

Disclosure: I have no financial conflict of interest to this blog entry.

Last updated: Jan 10th, 2011

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18 Responses to “May-Thurner Syndrome”

  1. Nicole Guite says:

    I have May-Thurner syndrome, diagnosed 5 years ago. Initially I was being treated with Coumadin and Plavix, but Plavix was stopped 3 years ago because my physician thought it was not necessary. I was afraid I would end up with another clot, which I did within the first year of being off Plavix. They had to put more stents into the vein because I had narrowing, and so far I have 5 stents placed in that area. I have severe pain in my left leg all the time.

    • Stephan Moll says:

      Unfortunately, a number of venous stents close up again, and repeat opening up of the stent (balloon angioplasty) and additional stent placement may be necessary. This may very well have happened even if Plavix (=Clopidogrel) had been continued alongside with Coumadin (=warfarin).

  2. michelle says:

    Hi Dr. Moll, I tried to get an appointment with you for my daughter, but you do not see children. My daughter was 11 when she got her DVT in August in her left femoral vein. Her first doctor only put her on Lovenox for 2 months, the clot grew in Feb. from 7cm to 11 cm, still only in her femoral vein. I brought her to a vascular surgeon who tested her with MRV for May-Thurner; he said she doesn’t have it, but the report reads that there is a mild compression of the iliac vein; I asked him about it and he said this is normal. Can you tell me more about that or any insight on why she would clot at this age? She has tested negative for all clotting disorders.

    • Stephan Moll says:

      DVT due to May-Thurner syndrome is typically in the pelvic vein, called the common iliac vein. You describe that your daughter had a clot in the femoral vein, i.e. the thigh. This is much lower down in the leg and would, thus, be much less likely due to May-Thurner compression in the pelvic area. A mild compression of the common iliac vein is, indeed, quite common, and typically irrelevant. An indicator of whether the narrowing might be clinically significant is whether collaterals are seen on the MRV scan, i.e. vessels that bypass the narrowing to drain the leg. If none are present then that is another indicator that the mild narrowing see on the MRV is clinically not relevant.

      As to why your daughter had a DVT in the first place: I would assess her for the usual DVT risk factors and do a thrombophilia work-up in her. The difficult and far-reaching decision is how long she should be treated with “blood thinners”.

  3. michelle says:

    Dr. Moll, thanks so much for your quick response. Do you think an MRV is good enough to assess for May Thurner syndrome? Or should I get her a venogram or another test? Do you think a mild compression can cause a DVT? THanks in advance for your expertise, this has been grueling on us, my daughter is very athletic and has had to give up a lot while on the Lovenox.

    • Stephan Moll says:

      A more sensitive method to look for May-Thurner syndrome is with intravascular ultrasound (IVUS), to include pressure measurements on both sides of the narrowing, i.e. the distal or caudal part, and the proximal or cranial part. That gives a better assessment whether there is a relevatn narrowing with pressure build up, i.e. obstruction. However, the patient is not very symptomatic, one would not typically stent a narrowing, no matter how signifciant it is, as it is not known whether stenting decreases the risk of recurrent DVT one the patient is off “blood thinners”. Thus, it may not really matter whether the patient’s DVT was caused by May-Thurner syndrome or not, as the treatment would be the same, no matter whether May-Thurner syndrome is present or not. I would make sure she gets to see a thrombosis-interested physician; best would be a pediatric hematologist. You seem to live close to Philadelphia – Dr. Leslie Raffini at the Children’s Hospital of Philadelphia, tel 1-800-879-2467, would be the best one to see.

  4. Sarah Simmons says:

    Good morning, I am writing to you with hope that you may help me with some answers to my questions. My daughter, who is 12yrs old, was rushed into hospital 7wks ago with major leg pain and unable to walk/move or have it touched. After a week of tests they finally found that she has a very large blood clot in her femoral vein (she also has 2 bone growths on her thigh bone but the have dismissed these??). This is the first case they have ever come across so they are treating her as they would an adult as they don’t know what else to do. At the moment she is on warfarin (she has been on it for 6wks now) and has daily injections of Heparin – her INR now is 2.8-, but nothing else has been done. We were sent home from the hospital with advice on how bad it is and how we have to be extremely careful!!! (found the rest of advice on the internet). She is still in major pain and still the same as when she first went into hospital. I am hoping you can give me names of tests and treatments so I can tell her doctor (as I live in England)
    Many thanks.

    • Stephan Moll says:

      In the patient with a leg DVT that is causing a lof of symptoms, one can consider treatment with clot-busters (= fibrinolytic therapy, such as tPA). However, this is most successful in the acute setting, i.e. in the first 2 weeks after symptoms of the blood clot first occurred.

      If leg symptoms are still quite marked after several weeks or months of treatment with “blood thinners”, a few things should be considered. (a) Is the patient wearing compression stockings? These should be tight, 30-40 mm graduated, individually-fit medical stockings. (b) Does the patient have a narrowing of the veins in the pelvis, that prevents the the leg from being drained. If the DVT is in the left leg, this is not uncommonly due to the so-called May-Thurner syndrome (narrowing of the main left pelvic vein; see explanation elsewhere in this blog). Clot-busters and other vascular interventional procedures (catheter-directed thrombectomy) can still be considered after a few weeks, as can balloon widening (angioplasty) or stenting of the narrowed vein. In the 12 year old patient above: She should be seen by a pediatric hematologist or other pediatric vascular specialist, who has seen other children with DVTs.

  5. Dot says:

    I found this info. Very interesting – many years ago after delivering one of my children – I do not remember the delivery but when I put my right leg over the bed the first time the pain was sooo severe – I mentioned to Doctor and he said something about how and where I carried the baby. My children are grown but I am prone to blood clots in that leg – find interesting.

    • Stephan Moll says:

      The narrowing of the pelvic vein in May-Thurner syndrome only occurs on the left side; so DVT associated with May-Thurner is a left leg DVT. Thus, your right problems are not explained by May-Thurner syndrome.

  6. Bonnie says:

    Maybe some one can help. I am a 27 year old female who was diagnosed with May-Thurner syndrome in 2007 and a stent was placed in my vein a few months later. I still have a lot of pain in my leg as well as swelling and I’ve noticed lately that when ever i stand day or night afer sitting or lying for just minutes i get severe pain in my heels and ankles. Could this be related? A little more background information: I have one 6 year old son born 2005 and I am also a full time nursing student and work as a pca on a MRU and one of the largest hospitals in my area so I am always on my feet…

  7. Dani says:

    I was diagnosed with May-Thurner syndrome (MTS) in 2009 and I have not had any stents placed, and was taken off Coumadin 1 year after DVT. I cannot find a doctor to place stents because i also have Factor V Leiden (FVL). Looking for a doctor to actually place stents, as I have MTS, FVL and am not on any thinners. Most doctors just say they will not do it with FVL as well, as they don’t know what will happen. Any suggestions?

    • Stephan Moll says:

      The reason to place a stent is to improve leg symptoms of swelling and pain, not to decrease the risk for recurrent clot. The decision whether to place a stent/stents is typically made independent on whether a patient has an underlying clotting disorder (thrombophilia) or not.

  8. Kim says:

    Hi Dr Moll…..I was diagnosed with DVT and PE 3 weeks ago……the DVT being in the groin of the left leg…..Now, I have an extruded disk in my back at L5/S1. What are the chances that this could be CAUSING the left iliac vein to be compressed worse than it normally would and not actually be classified as May-Thurner? I live in RI so I’m close to Boston…..any suggestions? I’ve thought about Lahey Clinic? Or is there someplace better? I want someone who knows what they’re talking about. Thank you so much in advance for your help. Have a nice day.

    • Stephan Moll says:

      A protruded disc is anatomically NOT close to the deep veins in the left pelvis and, thus, would not be the cause of a DVT. Unless the protruded disc led to pain and, thus, immobility. Then the immobility would be a contributor to the DVT.

      Dr. Simon Mantha at the Lahey Clinic would be a good person to see for the DVT.

  9. Jackie says:

    My daughter has been struggling with pain in her groin and leg. Doctors have discovered a narrowing in her iliac vein and have suggested Mays Thurner Syndrome but without evidence of a blood clot a definitive diagnosis has not been made. On a recent visit to the hospital because of pain the doctors found that she is pregnant. It was a surprise to her as exciting as it is worrisome. She is in need of a doctor who understands these issues and we do not know where to turn. We are in the Chicago area.

    • Stephan Moll says:

      Sounds like it is unclear why she has pain in her groin and leg. May-Thurner syndrome classically does not cause pain. She needs a good internist who can put things together.