A recent study found that the size of a brain aneurysm is not the main factor influencing its risk of rupture. An aneurysm forms when a blood vessel structure in the brain is damaged and locally protrudes. If a cerebral aneurysm ruptures, it can lead to a hemorrhagic stroke, which can cause brain damage or death. In Finland, lifelong follow-up of patients with cerebral aneurysms has shown that approximately one-third of all cerebral aneurysms rupture, and one-quarter of these are small aneurysms. The size of the aneurysm had a slight effect on the risk of rupture, especially in male patients. The risk of rupture was particularly high for female patients who smoked and for cerebral aneurysms of 7 mm or more in diameter. The risk of rupture was unexpectedly low in non-smoking men with cerebral aneurysms. Study author Dr. Seppo Juvela of the University of Helsinki said in a news release, “This does not mean that brain aneurysms in male nonsmokers will never rupture. It suggests that not every case of a brain aneurysm in men who are nonsmokers and have low blood pressure values needs to be treated.” Previous short-term studies have reported that the size of a brain aneurysm is the most significant predictor of the risk of rupture. This has led clinicians not to treat some small aneurysms that are less than 7 mm in diameter.