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May-Thurner syndrome: Iliac Vein Compression Syndrome
Author: Jeffrey S. Goldsmith M.D.
Last Revised: Wed, 06-Jun-2012
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May-Thurner syndrome: Iliac Vein Compression Syndrome

Jeffrey S. Goldsmith M.D.

Case Report

A previously healthy 30-year-old female presented to the emergency room with two days of left groin pain and increasing swelling of the lower leg.  She became acutely dyspneic with minimal exertion, and lightheaded with substernal chest pain. A pulmonary CT angio-gram revealed multiple pulmonary throm-boemboli within the bilateral intermediate and multilobar segmental and subsegmental arteries. The scan did not extend to the pelvis.  Venous duplex ultrasound was free of deep venous thrombosis in the bilateral lower extremities, however decreased blood flow velocity in the left common femoral vein was noted, suggesting a more proximal venous system obstruction.  The patient received treatment initially with unfract-ionated heparin, and then transitioned to Enoxaparin injections. Prior to initiating Warfarin, an extensive hypercoagulable workup was initiated including factor V Leiden muta-tion analysis, prothrombin 20210A variant mutation analysis, protein C activity, protein S antigen, antithrombin III level, homocystine level, antiphospholipid antibodies, ANA, diluted Russell's viper venom time. 

The patient’s symptoms of groin pain and dyspnea promptly improved within 3 days of treatment. She was ambulatory with normal hemodynamics and felt to be stable for out-patient management on Enoxaparin while transitioning to Warfarin.  By the seventh day of Enoxaparin, her INR was therapeutic at 2.7 seconds and the injections were discontinued. 

Approximately one week after discontinuing the Enoxaparin, the patient developed recurrent symptoms of left sided groin pain.  Her INR was 3.0 seconds.  A repeat duplex ultrasound of the lower extremity demonstrated acute deep venous thrombosis in the left proximal common femoral vein not previously noted. Enoxiparin was resumed and Warfarin was discontinued. 

The patient’s hypercoagulable work-up was entirely normal.  Her only medication was an oral contraceptive, and she had been taking this uneventfully for 9 years. This was discontinued  at the time of her initial admission.   She had no family history of venous thromboembolic disease.   She had one uneventful pregnancy four years earlier with vaginal delivery, and one remote first trimester miscarriage.  Prior to her initial presentation, she had no significant complaints, recent illness, weight changes or prolonged travel.  

An MR venogram was obtained to assess the iliac venous system.  The right common iliac artery was noted to cross the left common iliac vein. At the point of crossing, the common iliac vein appeared occluded, but without visible intra-luminal thrombus.  There was however thrombus noted in the left external iliac and left common femoral vein. These findings were consistent with May-Thurner syndrome.   Ultimately, thrombolysis of the areas of clot was performed.  Subsequently, the region of stenosis in the left common iliac vein was successfully angioplastied, and then an appropriate stent was placed. The patient was maintained on Enoxeparin for an additional month and gradually transitioned back to Warfarin.  At the 6-month follow-up, the patient was found to be symptom free. Her stent remained patent, and Warfarin therapy was continued for approx-imately a year. At that point repeat ultra-sonography showed no evidence of deep venous thrombosis, and anticoagulation was discon-tinued. She remains off oral contraceptives and symptom free.


Symptomatic compression of the left common iliac vein by the right common iliac artery, leading to subsequent deep venous thrombosis was first described by May and Thurner in 22% of patients in an autopsy series [1]. They hypothesized that repetitive compression of the left iliac vein from pulsations of the overlying right common iliac artery had lead to scarring and ultimately stenosis of the left iliac vein.


In up to 50% of patients with left iliac vein thrombosis, this iliac vein compression syndrome has been documented[3].  Compression of up to 50% of the vessel has been demonstrated in a quarter of asymptomatic patients studied without incidence of thrombosis.  The compression of the left iliac vein itself may be an anatomic variant, and alone is not necessarily a pathological condition.  The pro-portion of those who will advance to develop thrombosis remains unclear. In the relatively small studies, the incidence appears to be higher in women compared with men, and peak age of onset of thrombosis occurs between the third to fifth decades of life4-6

In the patient described above, venous duplex ultrasonography failed to demonstrate an acute thrombosis. While decreased velocity of the common femoral vein was noted on this patient’s initial study, adequate visualization of the iliac vessels with this technique is very limited7.  When the patient developed recurrent deep venous thrombosis within a week of bridging Warfarin therapy, MR venography was obtained to assess for iliac vein compression syndrome.  MR venography has similar sensitivity and specificity to invasive venography8.  Clot burden was noted in the adjacent external iliac vein, along with stenosis of the common iliac vein.  As a result, thrombolysis and subsequent angio-plasty and stent support of the compressed left common iliac vein was performed. This approach is a viable means of preventing recurrent thrombosis and limb threatening complications from thromboses9-10. While studies published are observational only, they demon-strate that thrombolysis of early clot burden can preserve valvular function and reduce risk of venous insufficiency11.While long term outcomes of venous angioplasty for patients with May-Thurner syndrome are lacking, reports of low complication rates, as well as patency rates of 79-100% have been noted  up to three years after angioplasty procedures are performed9-10.

Iliac vein compression syndrome, or May-Thurner syndrome, should be considered if no other hypercoagulable state or a left sided recurrent deep venous thrombosis is noted.  It is important to be aware of the limitations of routine lower extremity duplex ultrasonography in describing pelvic vein thrombosis, and consider alternate imaging techniques to help clarify anatomy of concern more proximal to the thigh deep venous system.


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  7. Messina LM, Sarpa MS, Smith MA, Greenfield LJ. Clinical significance of routine imaging of iliac and calf veins by color flow duplex scanning in patients suspected of having acute lower extremity deep venous thrombosis. Surgery. 1993 Nov;114(5):921-7. PubMed PMID: 8236016.
  8. Evans AJ, Sostman HD, Knelson MH, Spritzer CE, Newman GE, Paine SS, Beam CA.  1992 ARRS Executive Council Award. Detection of deep venous thrombosis: prospective comparison of MR imaging with contrast venography. AJR Am J Roentgenol. 1993 Jul;161(1):131-9. PubMed PMID: 8517292.
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  11. Augustinos P, Ouriel K. Invasive approaches to treatment of venous thromboembolism. Circulation. 2004 Aug 31;110(9 Suppl 1):I27-34. Review. PubMed PMID: 15339878.

Submitted on February 17, 2012

May-Thurner syndrome: Iliac Vein Compression Syndrome
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