What is May-Thurner syndrome?

What is May-Thurner Syndrome?

May-Thurner syndrome (MTS) is an anatomical variant where the left common iliac vein is compressed between the overlying right common iliac artery anteriorly and the lumbar vertebral body posteriorly, leading to venous stenosis that predisposes patients to deep vein thrombosis (DVT), particularly in the left lower extremity. 1

Anatomic Basis

• The compression occurs at a specific anatomical location: the left common iliac vein is trapped between the right common iliac artery and the lumbar spine 2, 3
• This anatomical variant affects approximately 22% of the general population, though most remain asymptomatic 4
• Variations exist where the right lower limb can be affected, though this is less common 3

Clinical Presentation

MTS should be suspected in young, otherwise healthy patients presenting with acute left-sided iliofemoral DVT, especially when unprovoked or recurrent. 5

• Most patients with partial obstruction remain asymptomatic throughout their lives 2
• When symptomatic, patients typically present with left lower extremity DVT (76.5% in pediatric cohorts) 4
• The condition shows a female predominance, particularly in postpartum women, multiparous women, and those using oral contraceptive pills 2
• Additional risk factors include spinal abnormalities like scoliosis, prior aortoiliac vascular stent placement, dehydration, and hypercoagulable states 2

Pathophysiology and Complications

• The chronic compression leads to venous stasis, intimal hyperplasia, and eventual thrombus formation 3
• Progression can result in extensive symptomatic DVT and/or chronic venous insufficiency 2
• Post-thrombotic syndrome (PTS) develops in a significant proportion of patients—62% in one pediatric cohort—when treated with anticoagulation alone 4
• Recurrent venous thromboembolism occurs more frequently with anticoagulation alone compared to those who undergo thrombectomy and iliac vein stenting 5

Diagnostic Approach

Duplex ultrasound is the first-line imaging modality for suspected DVT, though it may not adequately visualize the common iliac vein compression itself. 1

• CT venography or MR venography should be performed when MTS is specifically suspected to directly visualize the iliac vein compression 5, 1
• Catheter-based venography with intravascular ultrasound (IVUS) is typically reserved for patients undergoing intervention, as IVUS is the most sensitive and specific modality for deep vein obstructive disease 5
• A critical pitfall: up to 10% of significant stenotic lesions cannot be visualized by IVUS alone and require trial balloon angioplasty to unmask the stenosis 5

Clinical Significance

• MTS is an under-diagnosed condition that clinicians must consider in the differential diagnosis of younger adults with recurrent DVTs or unprovoked thromboembolic events 6, 3
• The syndrome can cause severe morbidity in symptomatic individuals, most commonly through DVT and post-thrombotic sequelae 3
• Early recognition is crucial because the underlying anatomic compression requires specific treatment beyond anticoagulation alone to prevent recurrent thrombosis 5