May-Thurner Syndrome

May-Thurner syndrome is the compression of the iliac vein against the lumbar spine by an overlying iliac artery, resulting in venous insufficiency, stenosis, and obstruction. While May-Thurner syndrome may be asymptomatic, typical symptoms include pain, swelling, and skin changes in the ipsilateral lower extremity. There are several variants of May-Thurner syndrome; the most common is compression of the left common iliac vein by the right common iliac artery. May-Thurner syndrome may be thrombotic or nonthrombotic but should be considered in all persons presenting with an iliofemoral deep venous thrombosis (DVT).  Rudolf Virchow first reported compression of the left iliofemoral vein by the right common iliac artery in 1851 after cadaveric studies of patients with left iliofemoral thrombosis. However, it was not until 1957 that May and Thurner reported intraluminal fibrous bands within the left iliofemoral veins compressed by the right common iliac artery in 22% of 430 dissected cadavers; these bands were labeled "spurs," and the collection of findings was termed May-Thurner syndrome. Cockett and Thomas were the first to report May-Thurner syndrome in living patients. Cadaveric and radiographic studies have reported a high prevalence of left iliofemoral vein compression by the right common iliac artery; the prevalence is so high that some consider the findings a normal anatomic variant. Any symptoms that occur, however variable, all stem from the compressive effect of the artery on the vein. The vascular compression impedes venous return, induces endothelial injury, and may progress to thrombotic vascular occlusion. The stereotypical patient with May-Thurner syndrome is a young woman with the acute onset of left lower extremity swelling following stasis, surgery, or during the intrapartum or immediate postpartum periods. While not all cases of May-Thurner syndrome result in DVT, up to two-thirds of iliofemoral DVTs demonstrate venous spurs. DVT in this clinical context may present acutely, and the thrombus frequently propagates distally into the femoral and popliteal veins to create a sizeable thrombotic burden. Pulmonary embolism may accompany the DVT. The treatment goals in symptomatic May-Thurner syndrome are to reestablish venous flow, alleviate strictures and venous hypertension, and reduce the incidence of postthrombotic syndrome. Anticoagulation or catheter-directed therapy with mechanical lysis is always followed by vascular stenting due to the irreversible fibrotic nature of the syndrome.