A thoracic aortic aneurysm is a weakened area in the upper part of the aorta. The aorta is the major blood vessel that feeds blood to the body.A thoracic aortic aneurysm may also be called thoracic aneurysm and aortic dissection (TAAD) because an aneurysm can lead to a tear in the artery wall (dissection) that can cause life-threatening bleeding. Small and slow-growing thoracic aortic aneurysms may not ever rupture, but large, fast-growing aneurysms may rupture.Depending on the size and growth rate of your thoracic aortic aneurysm, treatment may vary from watchful waiting to emergency surgery. Ideally, surgery for a thoracic aortic aneurysm can be planned if necessary.