May-Thurner Syndrome: Ultrasound Signs of Compression of the Left Common Iliac Vein
Pathogenesis and Clinical Significance
May-Thurner Syndrome is the chronic compression of the left common iliac vein between the right common iliac artery (anteriorly) and the vertebral body (posteriorly). Constant pulsatile trauma to the intima leads to fibrosis, formation of intraluminal 'spurs,' stenosis, and predisposition to thrombosis. Up to 20–25% (according to some data up to ~49%) of cases of left-sided iliofemoral venous thrombosis are associated with this syndrome. It is more common in women aged 30–40 years.
Important: Compression itself is present in ~70% of asymptomatic individuals ('permissive lesion'), so the significance lies not in the compression per se, but in its hemodynamic and clinical expression.
Classification by Types
| Type | Characteristic |
|---|---|
| Type I | Compression of the left common iliac vein by the artery (without fibrosis) |
| Type II | Compression + intraluminal fibrous adhesion ('spur') |
| Type III | Thrombosis with chronic post-thrombotic stenosis |
Features of Ultrasound Diagnosis
Iliac veins are a transitional zone between the legs and the IVC, where duplex works differently: direct visualization is challenging (depth, bowel gas, arterial overlap). Therefore, proximal obstruction is more often identified by indirect signs — changes in the spectrum in the common femoral vein (CFV).
Indirect Ultrasound Signs
Key indirect signs of hemodynamically significant obstruction of the left iliac segment:
- Reduced respiratory phasicity and cardiac-synchronous notches in the left CFV with preserved phasicity on the right;
- Venous ratio (VR) through the narrowing zone >2.5 (in the provided clinical example VR 2.9 with positional dynamics);
- Narrowing >50% according to duplex data when selecting candidates.
In the vein report, it is recommended to use ratios (VR) and hemodynamic parameters, NOT the percentage of stenosis.
Tactics and Confirmatory Methods
Duplex performs selection (loss of phasicity, VR >2.5, narrowing >50%), but IVUS ultimately evaluates the lesion (area reduction >50%, by VIDIO criterion >61% diameter). Upon identifying indirect signs, it is recommended:
- CT/MR venography for confirmation and extent assessment;
- Upon confirmation and persistent symptoms — consultation with a vascular surgeon;
- When deciding on intervention — intravascular ultrasound (IVUS) for area reduction assessment and stent selection.
The best candidates for stenting are patients with venous ulcers or disabling venous claudication. After stenting, duplex monitors patency.
Frequently asked questions
Why can't direct visualization of the vein be relied upon in May-Thurner Syndrome?
Direct visualization of the iliac segment by duplex is challenging due to depth, bowel gas, and arterial overlap. Therefore, proximal obstruction is identified by indirect signs — changes in the spectrum in the common femoral vein.
What VR threshold indicates significant obstruction?
VR through the narrowing zone >2.5. In the provided clinical example, VR was 2.9 with positional dynamics.
What are the main indirect ultrasound signs?
Reduced respiratory phasicity and cardiac-synchronous notches in the left CFV with preserved phasicity on the right, VR >2.5, narrowing >50%.
What should be used in the vein report — percentage of stenosis or ratios?
For veins, use ratios (VR) and hemodynamics, NOT the percentage of stenosis.
What method is considered best for assessing non-thrombotic iliac lesions?
IVUS (intravascular ultrasound): area reduction >50%, by VIDIO >61% diameter. It ultimately evaluates the lesion and aids in stent selection.