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.
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.
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.
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.
- Kibbe MR et al. Iliac vein compression in an asymptomatic patient population. J Vasc Surg 2004;39:937-943.
- 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.
- 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.
- Berger A et al: Iliac compression syndrome treated with stent placement. J Vasc Surg 1995;21:510-514.
- 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.
- O’Sullivan GJ et al.: Endovascular management of iliac vein compression (May-Thurner) syndrome. J Vasc Intervent Radiol 2000;11:823-836.
- AbuRahma AF et al.: Iliofemoral deep vein thrombosis: conventional therapy versus lysis and percutaneous transluminal angioplasty and stenting. Ann Surg 2001;233:752-760.
- Heijmen RH et al.: Endovascular stenting in May Thurner syndrome. J Cardiovasc Surg 2001;42:83-87.
- 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.
- Knipp BS et al. Factors associated with outcome after interventional treatment of symptomatic iliac vein compression syndrome. J Vasc Surg 2007;46:743-749.
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