May–Thurner syndrome

Overview

May–Thurner syndrome (MTS), also known as iliac vein compression syndrome, is a vascular condition in which the right common iliac artery compresses the left common iliac vein against the lumbar spine. This anatomical anomaly can impair blood flow from the left leg, increasing the risk of deep vein thrombosis (DVT), chronic venous insufficiency, and leg swelling. The condition primarily affects young to middle-aged women, though it can occur in anyone.

May–Thurner syndrome was first described in the 1950s by Drs. May and Thurner, who discovered that many cases of unexplained left-sided DVT were caused by this anatomical compression. While MTS may remain asymptomatic in some individuals, others may experience significant complications requiring medical or surgical intervention.

Causes

May–Thurner syndrome results from a mechanical compression of the left common iliac vein by the overlying right common iliac artery, which presses the vein against the underlying lumbar vertebrae. This compression leads to:

• Venous outflow obstruction: Impaired blood flow from the left leg increases venous pressure.

• Endothelial injury: Chronic pulsatile compression can damage the vein wall and promote clot formation.

• Fibrous intraluminal spurs: Over time, the repeated trauma can result in the development of fibrotic bands inside the vein, worsening obstruction.

Risk factors and triggers that may contribute to symptom onset include:

• Prolonged immobility or sedentary lifestyle

• Pregnancy or postpartum state

• Use of oral contraceptives

• Major surgery or trauma

• Underlying clotting disorders

The anatomical variation that defines MTS is present in a significant portion of the population, but only a small percentage develop symptoms.

Symptoms

Symptoms of May–Thurner syndrome vary depending on the degree of venous compression and whether thrombosis has occurred. Common signs and symptoms include:

• Left leg swelling: Often worsens with prolonged standing or during the day.

• Leg pain or heaviness: May be dull, aching, or throbbing in nature.

• Varicose veins: Dilated superficial veins may develop due to elevated venous pressure.

• Skin changes: Hyperpigmentation, thickening, or ulceration in chronic cases.

• Deep vein thrombosis (DVT): Sudden onset of leg pain, swelling, warmth, and redness, most commonly in the left leg.

• Venous claudication: Pain in the leg during walking or exertion that improves with rest.

In many cases, MTS is discovered only after a DVT occurs. Left-sided DVT is more common in MTS due to the specific anatomical compression on the left iliac vein.

Diagnosis

Diagnosing May–Thurner syndrome requires a combination of clinical suspicion, imaging studies, and sometimes invasive testing. Diagnostic steps include:

• Doppler ultrasound:

  • Often the initial test to detect DVT or venous flow abnormalities in the legs.

• CT or MR venography:

  • Provides detailed images of the pelvic veins and arteries.

  • Can visualize compression of the left iliac vein and associated thrombosis.

• Intravascular ultrasound (IVUS):

  • A catheter-based technique used during venography to assess the degree of vein narrowing and guide stent placement.

• Catheter-based venography:

  • Considered the gold standard for confirming diagnosis and planning treatment.

A full evaluation should also include assessment of potential hypercoagulable states if DVT has occurred, particularly in younger individuals.

Treatment

The treatment of May–Thurner syndrome depends on the severity of symptoms, the presence of DVT, and the degree of vein compression. Management options include:

• Medical therapy:

  • Anticoagulation (e.g., heparin, warfarin, or DOACs) for patients with DVT to prevent clot propagation and recurrence.

  • Compression stockings to reduce leg swelling and prevent post-thrombotic syndrome.

• Endovascular intervention:

  • Catheter-directed thrombolysis: For acute DVT, this procedure delivers clot-dissolving medication directly to the thrombus.

  • Balloon angioplasty: Used to dilate the narrowed vein before stenting.

  • Iliac vein stenting: Placement of a metal stent in the compressed vein to restore normal blood flow and prevent recurrence.

• Surgical options:

  • Rarely required, but may include bypass grafts in complex or recurrent cases not responsive to endovascular therapy.

Treatment is often coordinated by vascular specialists and interventional radiologists. Post-procedural anticoagulation is typically continued for several months.

Prognosis

The prognosis for patients with May–Thurner syndrome is generally good, especially with early diagnosis and appropriate intervention. Most patients experience symptom relief and reduced risk of recurrent DVT after successful treatment.

Without treatment, chronic venous insufficiency, persistent leg swelling, and skin ulcers can develop, significantly affecting quality of life. Recurrent DVT and pulmonary embolism are also potential complications if left unaddressed.

With advancements in imaging and minimally invasive techniques, outcomes for MTS have improved significantly. Long-term follow-up may include periodic imaging to assess stent patency and continued monitoring for thrombotic complications.