What is the most common cause of brain aneurysms?

Genetics: Defect in cerebral arterial walls which are often genetically determined, especially at branch points of the major brain arteries are the locations from which aneurysms arise. Hypertension and cigarette smoking are also big risk factors, especially hypertension.

Many factors: There are many conditions and factors that can lead to the formation of brain aneurysms. The most common are smoking and uncontrolled high blood pressure. There are also genetic conditions including connective tissue disorders and polycystic kidney disease that can lead to aneurysm formation.