Abominal aortic aneurysm, also written as AAA and often pronounced 'triple-A', is a localized dilatation of the abdominal aorta, that exceeds the normal diameter by more than 50%. The normal diameter of the infrarenal aorta is 2 cm. It is caused by a degenerative process of the aortic wall, however the exact etiology remains unknown. It is most commonly located below the kidneys (infrarenally; 90%), other possible locations are above or at the level of the kidneys (suprarenal and pararenal). The aneurysm can extend to include one or both of the iliac arteries. An aortic aneurysm may also occur in the thorax.