Abnormal dilatation of the thoracic or abdominal aorta; in ascending aorta most commonly secondary to medial degeneration (e.g., familial, Marfan’s syndrome, Loeys-Dietz syndrome, Ehlers-Danlos syndrome type IV, bicuspid aortic valve); aneurysms of descending thoracic and abdominal aorta are primarily atherosclerotic. Rare causes of aneurysms are infections (syphilis, tuberculosis, mycotic), vasculitis (e.g., Takayasu’s arteritis, giant cell arteritis), and spondyloarthropathies (e.g., rheumatoid aortitis).