Acute aortic syndrome (AAS) describes a range of severe, painful, potentially life-threatening abnormalities of the aorta. These include aortic dissection, intramural thrombus, and penetrating atherosclerotic aortic ulcer. AAS can be caused by a lesion on the wall of the aorta that involves the tunica media, often in the descending aorta. It is possible for AAS to lead to acute coronary syndrome. The term was introduced in 2001.