A brain aneurysm develops in a weak or a defective artery wall, though the cause of this is not yet fully understood. It could be a degeneration process, where factors such as increasing age and high blood pressure play a crucial role. It is also often linked to atherosclerosis, which is a blood vessel disease that causes the arteries to hardened due to the accumulation of fatty deposits on the inside of the arterial walls.
Brain aneurysms commonly occur in people with particular genetic disorders including connective tissue disorder and polycystic kidney disease. Some circulation diseases, such as arteriovenous malformation, can also cause brain aneurysms. Other causes include excessive consumption of alcohol and drugs, head injuries, infection, and tumours.