An asymptomatic 26-year-old man was initially admitted with a suspicious mediastinal mass. On the basis of the contrast-enhanced chest CT findings, aneurysm formation involving the left cervical aortic arch associated with subaortic left innominate vein was diagnosed. The aneurysm was confirmed by MR angiography and DSA. The arch aneurysm was surgically removed. We describe this case, and review the literat