Aortic aneurysms. Rotating 3D computed tomography (CT) scan of a dissecting thoracic aortic aneurysm and an abdominal aortic aneurysm. The aorta is the main body artery, consisting of a thoracic (chest) section and an abdominal section. An aneurysm is a swelling of the artery wall, and can be fatal if it ruptures. A dissecting aneurysm is where the layers of the wall of an artery split or dissect, swelling and filling with blood.