In most instances (at least 70% of cases) AA develops when the wall is weakened by deposition of fat, inflammatory cells, calcium, and reactive division of the muscle layer cells of the aortic wall. This complex process is known as atherosclerosis or hardening of the arteries. Many enzymes which dissolve the extracellular matrix which hold the aortic wall together are generated as atherosclerosis progresses.
Smoking, diabetes, hypertension, increased cholesterol, are the commonest risk factors for atherosclerosis. AA are at least 5 times more common Males are 5 times more commonly affected than females.
Less frequently the cause is genetic, AA can run in families and a history of an AA should trigger aortic US screening of siblings.