Coloured computed tomography (CT) angiogram of a 61 year old patient with a thoracic aortic aneurysm. An aortic aneurysm is a swelling of the aorta, usually due to an underlying weakness in the wall of the artery. This may lead to rupture, causing severe pain, massive internal haemorrhage (bleeding), and, if left untreated, death. The size of the aneurysm is shown in millimetres on the scan.