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May-Thurner Syndrome


A congenital stenosis of the left main pelvic vein (= left common iliac vein) by pressure from the overlying right common iliac artery (image 1) is referred to as May Thurner syndrome. While this anatomic variant is a risk factor for DVT, in many people is causes no symptoms and is irrelevant.


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

Normal anatomy is that the right common iliac artery lies on top of the left common iliac vein (image 1). This close proximity leads, in some people, to pinching of the iliac vein between the artery in front and the vertebral body behind it, and to varying degrees of left iliac vein stenosis. It is not a disease, but a congenital anatomic variant.


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 left 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 stenosis, and half have nearly 50 % narrowing (reference 1). However, how common severe stenosis of 90 % or more is, is not known.


Many people with May-Thurner syndrome have no symptoms, even if they have pronounced stenosis. This is because other, smaller veins bypassing the stenotic area form effective collaterals. Some people with severe stenosis have leg swelling and pain, and sometimes stasis ulcers, i.e. symptoms of chronic venous insufficiency. And some people are at increased risk for DVT if the left common iliac vein and left leg veins, particularly if other risk factors (such as pregnancy, contraceptives or clotting disorders) are also present.


Routine Doppler ultrasonography of the legs can typically not discover May-Thurner syndrome, as the pelvic veins, i.e. those above the groin/inguinal ligament, can only be sub-optimally/poorly visualized. CT venogram (CTV) or MR venogram (MRV) are needed to make a diagnosis, or an invasive contrast venography 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 stenosis is coincidentally discovered and causing none or only mild symptoms. (b) In the patient who has chronic venous insufficiency or postthrombotic syndrome and who is found to have May Thurner syndrome, stenting of the stenosis (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 risk of recurrent DVT in the patient who had a DVT or PE and is found to have May-Thurner syndrome.

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

Since 1995 venous stents have been placed into the stenotic area (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.  They appear beneficial at least in the short-term improvement of symptoms, within the first 1-2 years of their placement (references 4-9). However, nearly 2/3rds of stents may close up within the first 5 years of their placement (ref 9). Repeat radiological procedures to re-open the stents can often be successfully performed, so that, 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) anticoagulants, and (b) whether aspirin has any benefit in keeping these stents open if anticoagulants are not given.

In the past, surgical procedures were done to take the pressure off the iliac vein by moving the overlying artery elsewhere, by performing (a) venous bypass surgery of the stenotic area, (b) dissection 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 typically recommend stent placement. Once a stent has been placed I recommend at least 3 months of anticoagulation. Thereafter, the decision to come off or stay on anticoagulants depends on the patient’s risk factors for recurrent venous thromboembolism (VTE), such as (a) what triggered the first VTE, (b) how many episodes of VTE the patient has had, (c) whether a strong thrombophilia is present, (d) whether the patient has residual clot in his/her legs, and (e) whether a D-dimer is positive or negative. If a decision is made to discontinue the anticoagulant, 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 patients

This same topic, discussed for patients and other non-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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7 Responses to “May-Thurner Syndrome”

  1. Sonia says:

    I have an 18 yr old with May-Thurner syndrome who presented 8 weeks ago with large L leg DVT/PE to an outside facility and underwent placement of IVC filter, thrombolysis and iliac vein stent. Currently on anticoagulation. Filter retrieval attempted but tines have penetrated IVC. Being evaluated by vascular surgery. My question is on duration of anticoagulation if filter is successfully removed, since CT now shows no clot. I assume he will need at least 3-6 months given PE and iliac vein stent.

    • Stephan Moll says:

      The decision on how long to treat with anticoagulation depends on (a) the risk factors that led to the first episode of venous thromboembolism, (b) the persistent risk factors, and (c) how a patient tolerates anticoagulant therapy and what his/her preference is. The stent may be a risk factor for recurrence; the IVC filter, if it cannot be removed, would be another (probably mild) risk factor for recurrence [ref 1]. I would, indeed, treat for 3-6 months, and then make a decision on discontinuation or continuation of anticoagulation based on points a-c above.

      The PREPIC Study Group. Eight-year follow-up of patients with permanent vena cava filters in the prevention of pulmonary embolism: the PREPIC (Prévention du Risque d’Embolie Pulmonaire par Interruption Cave) randomized study. Circulation. 2005; 112:416–422.

  2. Karen F. P. says:

    Hello Dr. Moll,

    I have May Thurner (discovered in May 2008, have a stent on left iliac vein), am 38, an have recently married and would like to start a family. What is your take on the potential risks of pregnancy while having this condition, and might you have any recommendations other than, say, adopting? 🙂 thanks for your time.


    • Stephan Moll says:

      Published Data:
      There are no formal treatment guidelines or consensus statements for this situation. I am aware of only one (small) publication that investigated 6 women with stents in their pelvic veins who became pregnant [ref 1]. They received a low dose of “blood thinner” starting at week 12 of pregnancy and given throughout pregnancy and for 4 weeks after delivery. They were asked to preferentially sleep o the right side, to avoid pressure of the pregnant uterus onto the right pelvic veins where the stents were. No DVT (deep vein thrombosis) or PE (pulmonary embolism) occurred. Examinations with ultrasound showed that the stent was compressed towards the end of the pregnancy in some of the women, but this resolved after delivery.

      My Approach:
      I would view a stent in the pelvic area, placed to treat May Thurner syndrome, as one of the potential risk factors for recurrent DVT. I typically would not advise against pregnancy, but would treat the woman with some “blood thinner” (low molecular weight heparin) throughout pregnancy and for some time period after delivery. Whether to use a low dose or a high dose would depend on what other risk factors for DVT the woman has and what her previous history is:
      a) Did the patient ever have a DVT or was the stent “just” placed because of leg symptoms (pain, swelling) without evidence of previous DVT?
      b) If she previously had a DVT, what were the risk factors associated with it?
      • Was it an unprovoked (idiopathic) DVT?
      • Birth control pill, patch or ring, hormone therapy, pregnancy
      • Major surgery, immobility, or trauma?
      • Was the patient worked up for a clotting disorder (thrombophilia)?
      • Is the patient obese, does she smoke?
      • Is she on long-term “blood thinners”?
      • Does she have chronic leg swelling and, if yes, how severe is it?
      • Has she ever been pregnant before?

      Hartung O et al. Management of pregnancy in women with previous left ilio-caval stenting. Journal of Vascular Surgery 2009;50:355-359.

  3. Ann says:

    Hi, In November 2010 I was hospitalized with PE’s in both pulmonary arteries and found to have extensive DVT in my left leg. I have no risk factors, other than age (I’m 51) and had only mild swelling in my left leg.An abdo CT showed some evidence of iliac vein compression and I was started on Lovenox then moved onto Coumadin. Although my INR was therapeutic (between 2.2 and 2.9) I got another PE so was put back on Lovenox and a retrievable ivc filter was fitted. Now several months later I’m scheduled for a venogram and possible stenting. If stented should I try Coumadin again or stay on Lovenox? (vascular surgeon suggested Coumadin, PCP and hematologist think stay on Lovenox until 12 moths post initial PE). Should I contemplate having the ivc filter removed? After finishing the 12 months of anticoagulation should I have any long term anticoagulant? Evidence seems to be thin in this area so your opinion would be appreciated.