Color Doppler U/S vs MSCT Venography in May-Thurner Syndrome

Inclusion Criteria: * advanced chronic venous insufficiency submitted to clinical treatment for at least 1 year with no response. * Subject must be \> 18 and \< 80 years of age. * informed consent document before the planned procedure. * On duplex ultrasound: patent common femoral vein, and patent deep femoral vein, and/or femoral vein of the study leg. Exclusion Criteria: * Previous venous stent implantation involving the study leg or inferior vena cava * Previous venovenous bypass surgery involving the study leg * Known reaction or sensitivity to iodinated contrast that cannot be managed with premedication. * Subjects who are pregnant (women of childbearing potential must have a negative pregnancy test within 7 days prior to enrollment). * Acute deep venous thrombosis involving either leg. * Known history of chronic total occlusion of the common femoral vein of the study leg. * Venous compression caused by tumor encasement. * Venous outflow obstruction caused by tumor thrombus. * Elevated baseline blood creatinine (value greater than the upper limit of the normal range).