May-Thurner Syndrome: Causes, Symptoms and Treatment

May-Thurner syndrome is a condition in which the right common iliac artery compresses the left common iliac vein against the lower spine, narrowing the main channel that returns blood from the left leg to the heart. Many people have this anatomical arrangement without ever developing symptoms. In others, the compression slows venous return enough to cause persistent swelling and discomfort in the left leg or to contribute to a deep vein thrombosis (DVT) in the pelvis and thigh. The condition is also known as iliac vein compression syndrome or Cockett syndrome. It is frequently identified only after a clot has already formed.

How Iliac Vein Compression Develops 

Within the pelvis, the right common iliac artery crosses in front of the left common iliac vein at approximately the level of the fifth lumbar vertebra. With every heartbeat, the artery presses the vein against the bone behind it. Over many years this repeated pulsation may cause the inner lining of the vein to thicken and form fibrous bands, sometimes called venous spurs, which further restrict flow.

May and Thurner described these changes in 1957 after examining 430 cadavers, finding obstructive lesions in roughly one in five left iliac veins. Later imaging studies have confirmed that some degree of left iliac vein compression is common in the general population. The distinction between anatomy and disease is therefore important, because compression becomes a clinical syndrome only when it produces symptoms or contributes to clot formation.

Risk Factors for Symptomatic May-Thurner Syndrome 

Symptomatic May-Thurner syndrome is diagnosed more often in women and most commonly in early to middle adulthood. Conditions that increase the tendency of blood to clot appear to unmask the narrowing in susceptible individuals. These include pregnancy and the weeks after delivery, estrogen-containing contraceptives or hormone therapy, recent surgery, prolonged immobility, dehydration and inherited clotting disorders. An unexplained DVT in the left leg, particularly one involving the iliac or femoral veins, is among the strongest reasons to consider the diagnosis.

Common May-Thurner Syndrome Symptoms 

Because the compression affects the vein draining the entire left leg, symptoms are typically one-sided. They may develop gradually over months or appear suddenly when a clot forms.

Chronic Symptoms of Iliac Vein Compression 

Long-term obstruction raises pressure in the veins below the narrowing, producing changes similar to other forms of venous disease:

• Swelling of the left leg that worsens through the day and improves with elevation
• Aching, heaviness or a bursting sensation in the thigh or calf after walking, known as venous claudication
• Varicose veins in the left leg, sometimes returning after previous treatment
• Brown discoloration, thickened skin or ulcers near the ankle in longstanding cases

Deep Vein Thrombosis Associated With May-Thurner Syndrome 

For many patients the first sign is a DVT. A clot associated with iliac vein compression often extends from the pelvis into the thigh, causing sudden swelling of the whole left leg together with pain, warmth and a reddish or bluish skin tone. These features overlap with other presentations of deep vein thrombosis symptoms, so imaging is needed to establish the cause. Published case series have identified iliac vein compression in a substantial proportion of patients with left-sided DVT, which is why the pelvic anatomy is often examined once a clot in this location has been confirmed.

Warning Signs of Pulmonary Embolism 

A clot in the leg can travel to the lungs and cause a pulmonary embolism. Call 911 for any of the following:

• Sudden shortness of breath or rapid breathing
• Chest pain that worsens with a deep breath or cough
• Coughing up blood
• A racing or irregular heartbeat
• Lightheadedness or fainting

New, rapidly worsening swelling of one leg should also be assessed by a medical professional the same day.

Diagnosing May-Thurner Syndrome 

Evaluation begins with a review of symptoms and medical history together with a comparison of both legs. Duplex ultrasound is usually the first test, since it can confirm or exclude a clot in the thigh and calf veins and show whether flow from the leg appears restricted further upstream. New one-sided swelling is one of the situations in which leg symptoms warrant a vascular ultrasound. The view of the deep pelvic veins can be limited by bowel gas and body size, however, so additional imaging is often required.

CT venography and MR venography produce cross-sectional images of the pelvis that can show narrowing of the iliac vein and its relationship to the overlying artery. Catheter venography combined with intravascular ultrasound (IVUS), in which a small probe is passed inside the vein, measures the degree of narrowing most precisely and is often performed at the time of treatment. Because compression may exist without causing symptoms, imaging findings are always interpreted alongside the clinical picture.

May-Thurner Syndrome Treatment Options 

Treatment is generally reserved for people with symptoms or a related clot. Compression found incidentally on a scan in someone without symptoms does not usually require intervention.

Treating Deep Vein Thrombosis 

When May-Thurner syndrome presents with DVT, anticoagulant medication forms the foundation of care because it limits extension of the clot and lowers the risk of embolism. For extensive clots involving the iliac and femoral veins, a specialist may consider catheter-directed techniques that dissolve or remove the clot, particularly when symptoms are severe. Anticoagulation alone does not relieve the underlying compression, however. A persistently narrowed vein may raise the likelihood of recurrent clots and of post-thrombotic syndrome over time.

Venous Stenting for Iliac Vein Compression 

Venous stenting has become the most widely used treatment for symptomatic iliac vein compression. Through a small puncture, usually in the thigh or behind the knee, a flexible metal stent is positioned within the narrowed segment to hold it open. Antithrombotic medication is typically prescribed afterward for a period guided by the patient’s clotting history. Follow-up imaging then confirms that the stent remains open. Open surgical reconstruction is now uncommon and is reserved for selected cases.

The most suitable approach depends on symptom severity, the presence and age of any clot, bleeding risk and overall health. A vascular specialist providing deep vein thrombosis care can explain how these factors apply to an individual situation and which options are appropriate.

Final Consideration

Prime Vascular Care evaluates patients experiencing persistent one-sided leg swelling or suspected DVT at its Sterling and Woodbridge clinics. The evaluation begins with duplex ultrasound to assess blood flow and determine whether additional pelvic imaging is necessary. Patients traveling from Alexandria, Stafford and Hamilton can schedule a consultation to investigate the underlying cause of their symptoms and review suitable treatment options.