A 35-year-old woman presented with a 2-day history of progressive left lower extremity pain and swelling. She had started oral contraceptives 4 months prior, and had flu-like symptoms that required her to stay home for the past week. Physical examination confirmed marked swelling extending from the left ankle to the groin. An erythrocyanotic appearance existed throughout the involved limb. Duplex ultrasonography revealed acute thrombosis within the calf, popliteal, femoral, and common femoral veins. The iliac vein was technically difficult to insonate. Due to suspicion of a coexistent iliac deep venous thrombosis (DVT), a left lower extremity venogram was obtained that confirmed acute thrombosis within the left iliac and common femoral veins (Figure 55-1). This presentation and clinical constellation of signs and symptoms was consistent with May-Thurner syndrome (MTS).

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  A condition of predominantly left-sided DVT caused by compression of the left common iliac vein by the overlying right common iliac artery and underlying lumbar vertebrae (Figure 55-2).

  
  
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  More commonly found in women in their second to fourth decades of life.^{1,2, and 3}

  
  
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  About 50% of patients with left iliac vein thrombosis have documented left iliac vein compression.⁴

  
  
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  Hypercoagulable states are found in up to 67% of screened patients who have chronic iliac vein thrombosis.²

  
  
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  Affected patients often have a superimposed thrombotic trigger including recent trauma, pregnancy, oral contraceptives, or protracted immobilization.

  
  
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  Although the prevalence of MTS-associated DVT is unusually low (2%-3%), this statistic is probably a gross underestimation as the condition is frequently overlooked.

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  Iliac vein compression was first described in the 19th century by Virchow.

  
  
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  May and Thurner documented venous webs or “spurs” in 22% of the left iliac veins of cadavers.^1,4

  
  
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  Intimal proliferation and scarring (deposition of elastin and collagen) were attributed to compression of the left iliac vein by the pulsations of the overlying right common iliac artery.^2,4

  
  
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  Several other anatomic variants have been observed as the cause of compression thrombosis.^1,2

  
  
  
  
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    Left iliac vein compression by the left internal iliac artery

    
    
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    Right iliac vein compression by the right internal iliac artery

    
    
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    Inferior vena cava (IVC) compression by the right iliac artery

Clinical Features

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  Young female patients presenting with unilateral, usually left-sided, lower extremity pain and edema.^{1,2, and 3} These signs and symptoms involve not only the calf but the thigh as well.

  
  
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  Left hemi-inguinal and flank pain may occur.

  
  
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  May have signs of post-thrombotic syndrome (PTS) such as varicose veins, phlebitis, pigment deposition, recurrent skin ulcers, and chronic swelling (Figure 55-3).^{1,2, and 3}

  
  
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  Approximately half of MTS patients treated with conventional anticoagulation will ultimately develop lifestyle-limiting venous claudication.

  
  
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  A prethrombotic stenotic variant exists that is associated with similar manifestations.