Etiology of Abdominal Aortic Aneurysms Etiology of abdominal aortic aneurysms is multifactorial but commonly involves a weakening of the arterial wall, usually by Atherosclerosis Other causes include Trauma Cystic medial necrosis Postsurgical anastomotic disruption Vasculitis Uncommonly, syphilis and localized bacterial or fungal infection, typically due to sepsis or infective endocarditis, weaken the arterial wall and cause infected (mycotic) aneurysms.