What are the causes of brain aneurysm and how to prevent them?

Incompletely known: This is incompletely understood. It starts with a localized weakness in blood vessels, no known way to predict in whom. Risk factors include cigarette smoking, high blood pressure, increasing age, rare predisposing weaknesses of arteries known as "familial aneurysms" and some rare predisposing conditions, which your doctor should evaluate. If headaches are present, get screening with mri/mra.