下肢深層靜脈栓塞在臨床上是一個常見的疾病。它的發生不只常見危險因子：包含長期久站、臥床、年齡大、靜脈曲張、服用避孕藥、惡性腫瘤等，人體結構上的異常也是可能的原因。髂靜脈壓迫症候群(Iliac vein compression syndrome)，亦稱為May-Thurner syndrome，是一個極少被診斷的疾病，成因是左總髂靜脈受到右總髂動脈和後方腰椎的壓迫，造成靜脈血流滯阻。這個解剖異常約存在於20%的人口，但是常因病人有許多危險因子而未安排進一步的檢查，而沒有診斷出這個疾病。May-Thurner syndrome若症狀嚴重需置放支架，保持血管暢通才能避免復發。這篇個案報告是描述這個罕見被診斷的疾病，在臨床上病人有下肢深層靜脈栓塞，考量到這個重要疾病對病人會有很大的幫助。

Deep vein thrombosis as a common clinical syndrome finds its major risk factors in prolonged standing, immobility, old age, varicose veins, pregnancy, oral contraceptives, and cancer. However, an anatomical variant can also lead to blood clots in the lower extremity. May-Thurner syndrome, also known as iliac vein compression syndrome, is a rare condition in which the left common iliac vein is compressed by the right common iliac artery, thus increasing the risk of deep vein thrombosis in the left extremity. While this anatomic finding is present in over 20% of the population, most go undiagnosed as patients presenting with deep vein thrombosis have other accompanying risk factors. For severe May-Thurner syndrome, endovascular venous stenting may actually be necessary to prevent recurrence. In this case report, an 85-year-old woman with progressive swelling of left lower extremity was diagnosed with May-Thurner syndrome. When evaluating patients with unilateral leg pain and swelling, clinicians should keep in mind the possibility of May-Thurner syndrome as another possible risk factor of deep vein thrombosis.