A cerebral aneurysm occurs when one of the brain’s blood vessel walls weakens and bulges. This abnormal dilation is dangerous because it can press on the surrounding nerves and brain tissue or rupture, which is life threatening.

Most aneurysms do not have symptoms and are found when brain imaging has been conducted for other reasons. A large unruptured aneurysm may press on the surrounding nerves, causing numbness, weakness, or pain behind the eyes. A ruptured aneurysm causes subarachnoid hemorrhage, or bleeding into the brain. The most common symptom of a subarachnoid hemorrhage is a sudden, severe headache, most often described as “the worst headache of my life.” Anyone experiencing a headache like this should seek immediate medical attention, because ruptured aneurysms are a life-threatening medical emergency.