Definition: An abnormal balloon- or sac-like dilatation in the wall of the THORACIC AORTA. This proximal descending portion of aorta gives rise to the visceral and the parietal branches above the aortic hiatus at the diaphragm.
dissecting aneurysm: coordinate IM with ANEURYSM, DISSECTING (IM); rupture: coordinate IM with AORTIC RUPTURE (IM)