Atypical May-Thurner Syndrome Caused by Bone Spur of the L4∼5 Lumbar Vertebrae

May–Thurner syndrome (MTS) is a condition in which the left common iliac vein is irritated by chronic pulsatile compression between the right common iliac artery and the upper iliac or lumbar spine. It mainly causes swelling and pain in the left lower extremity, venous thrombosis, and repeated deep venous thrombosis. In patients with sudden swelling and pain in the left lower extremity and suspected lower extremity thrombosis, when no other obvious cause can be found, the possibility of MTS should be considered. We experienced a rare case of an older patient with atypical MTS caused by bone spur of the 4th and 5th lumbar vertebrae, which has been reported here along with a review of the literature.