May-Thurner Syndrome: An Anatomic Predisposition to Deep Vein Thrombosis

May-Thurner syndrome (MTS) is a rare clinical condition caused by extrinsic compression of the left common iliac vein by the right common iliac artery, leading to venous stasis and predisposing to thrombus formation. Here, we present the case of a 39-year-old female with no obviously known other risk factors predisposing to thrombosis who presented with severe left leg pain and swelling for a week. The international normalized ratio was elevated and the venous Doppler study showed extensive thrombosis extending from the left common iliac vein to the common femoral vein and the popliteal vein. She was diagnosed with MTS and treated with catheter-directed mechanical thrombolysis and thrombectomy, along with angioplasty of the left common iliac vein and external iliac vein, with near-complete resolution post-treatment. MTS should be suspected in patients who present with unilateral limb thrombosis regardless of the presence of predisposing factors. Timely management with endovascular procedures is necessary to help prevent other potential life-threatening complications.