What could cause an aneurysm?

Abdominal (AAA)?: We are not quite sure what actually causes an AAA to form in some people. The leading thought is that the aneurysm may be caused by inflammation in the aorta, which may cause its wall to weaken or break down. Most believe that this inflammation can be associated with atherosclerosis (also called hardening of the arteries) or risk factors for atherosclerosis, such as high blood pressure and smoking.

Cause of aneurysm: With the exception of a few genetic conditions like marfan's or ehlors danlos and a couple others we haven't established the exact cause of the vast majority of aortic or peripheral aneurysms.