What condition in young women causes left‑leg deep‑vein thrombosis with pain or heaviness when the leg is crossed?

May-Thurner Syndrome: Left-Leg DVT with Positional Pain in Young Women

The condition you're remembering is May-Thurner syndrome (MTS), an anatomical variant where the right common iliac artery compresses the left common iliac vein against the lumbar spine, causing left-sided deep vein thrombosis that presents with leg pain, swelling, and heaviness—symptoms that can worsen with leg crossing or certain positions. 1, 2, 3

Why the Left Leg and Why Women?

• The left common iliac vein is compressed by the overlying right common iliac artery against the fifth lumbar vertebra in MTS, creating a mechanical obstruction that predisposes to left-sided DVT in approximately 80% of pregnancy-related cases. 1

• Young women are disproportionately affected because hormonal factors (pregnancy, oral contraceptives) combined with the anatomical compression create a perfect storm for thrombosis. 4, 1

• Left leg symptoms are a powerful predictor: in pregnant women with confirmed DVT, left leg involvement had an adjusted odds ratio of 44.3 (95% CI, 3.2-609.7) for DVT diagnosis. 1

Clinical Presentation: The "Crossing Legs" Connection

• Patients experience pain, heaviness, and swelling in the left leg that can be exacerbated by positions that further compress the iliac vein—such as crossing the legs, prolonged sitting, or lying supine. 1, 5

• The mechanical compression reduces femoral venous blood flow, with the effect being more marked in the left leg veins, explaining the positional nature of symptoms. 1

• Classic presentation includes swelling of the entire left leg, sometimes with flank, buttock, or back pain when isolated iliac vein thrombosis is present. 1

Why This Matters Clinically

Young women presenting with unprovoked left-sided iliofemoral DVT should immediately raise suspicion for May-Thurner syndrome, as anticoagulation alone is inadequate treatment and leads to significantly higher recurrent VTE rates. 2, 4

The Critical Pitfall: Anticoagulation Alone Fails

• The anatomic compression persists despite anticoagulation, making mechanical relief of the obstruction essential—anticoagulation alone does not address the underlying structural problem. 2, 4

• Combined iliac vein stenting with catheter-directed thrombolysis (CDT) or pharmacomechanical thrombectomy (PMT) plus therapeutic anticoagulation is the preferred treatment, as anticoagulation alone results in recurrent VTE and post-thrombotic syndrome. 2, 3

Diagnostic Approach

• Duplex ultrasound is first-line for suspected DVT, but it often fails to visualize the iliac vein compression that defines MTS. 3, 6

• CT venography or MR venography must be performed when MTS is suspected to directly visualize the iliac vein compression and confirm the diagnosis. 3, 6

• In pregnant women with suspected DVT, initial evaluation should use proximal compression ultrasound with direct imaging and Doppler flow examination of the iliac veins if isolated iliac vein thrombosis is suspected. 1

Treatment Algorithm

Acute Presentation (DVT < 14 days)

1. Start therapeutic anticoagulation immediately upon diagnosis—preferably low molecular weight heparin in pregnant/postpartum women or direct oral anticoagulants in non-pregnant patients. 2, 7, 3

2. Perform catheter-directed thrombolysis or pharmacomechanical thrombectomy to remove thrombus burden before stenting (Class IIa recommendation). 2, 3

3. After thrombus removal, balloon angioplasty followed by self-expanding iliac vein stent placement is required, as angioplasty alone typically fails. 2, 4

4. Pharmacomechanical thrombectomy reduces required thrombolytic drug dose by 40-50% and shortens infusion time compared with CDT alone. 2

Post-Stenting Management

• Continue therapeutic anticoagulation with the same dosing and duration as for iliofemoral DVT without stents: minimum 3 months for provoked DVT, indefinite therapy for unprovoked events. 2, 7

• Direct oral anticoagulants are preferred over warfarin in non-cancer patients because they lower bleeding risk. 2

• Prescribe 30-40 mm Hg knee-high elastic compression stockings for at least 2 years to reduce post-thrombotic syndrome risk. 2

Special Population: Oral Contraceptive Users

• Women on oral contraceptives presenting with left-sided iliofemoral DVT should be screened for both hypercoagulable disorders and underlying May-Thurner anatomy. 4

• In a case series of 7 adolescent patients with previously undiagnosed MTS, all presented with DVT after initiating oral contraceptives (mean time 5 weeks, range 2-10 weeks). 4

• All patients treated with mechanical thrombectomy followed by stenting achieved 100% primary stent patency and complete resolution of symptoms with no recurrence at mean 13-month follow-up. 4

Long-Term Outcomes

• At 3 years after iliac vein stenting, 79% of young patients maintain pain reduction and 66% maintain swelling reduction, demonstrating durable symptom relief. 2

• Stent fracture occurs in only ~1% of cases and can be successfully managed by implanting a second stent. 2

• Among 62 women with left iliac vein stents who became pregnant while on low-molecular-weight heparin prophylaxis, none experienced recurrent VTE during pregnancy or postpartum. 2

When to Suspect MTS: Red Flags

• Young woman (especially < 50 years) with left-sided leg symptoms 2
• Unprovoked or recurrent left-sided DVT 3, 6
• Recent initiation of oral contraceptives or pregnancy 4, 1
• Symptoms worse with leg crossing or prolonged sitting 1, 5
• Swelling of entire left leg with or without flank/buttock pain 1

Do not delay endovascular intervention when MTS is identified—early thrombus removal within 14 days yields optimal outcomes, and failure to treat the anatomic compression predisposes to recurrent VTE and post-thrombotic syndrome. 2, 4