A brain aneurysm develops in a weak or defective artery wall, although the cause has yet to be fully understood. It could be a degeneration process, whereby factors such as ageing 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 harden due to the accumulation of fatty deposits on the inside of arterial walls.
Brain aneurysms commonly occur in people with certain genetic disorders such as 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.