A cerebellar aneurysm may occur when the walls of a blood vessel, or tube, in the brain becomes weak and results in the vessel ballooning out or bulging. Cerebral aneurysms may result from congenital (birth) defects, or other conditions such as high blood pressure, blocked arteries (atherosclerosis), and less commonly from head trauma or injury. The prevalence of cerebral aneurysms varies from one country to another, anywhere from five cases per 100,000 to 20 cases per 100,000. This condition is most common in people age 50-60. The size of the aneurysm, or ballooned part of the vessel, may be anywhere from 1/8 of an inch to over an inch in size, and typically, the larger the aneurysm, the more dangerous they can be. Aneurysms become dangerous when they rupture (burst) and cause bleeding in the brain. Symptoms of a ruptured aneurysm may include: migraines, nausea, vomiting, blurred vision, light sensitivity, and loss of strength or sensation. People with non-ruptured aneurysm often have no symptoms, but if symptoms do present they may include: dilated pupils, double vision, pain above and behind the eyes, headaches, and weakness or numbness. Cerebral aneurysms are diagnosed using a test called an angiogram or an MRI. Treatment varies from case-to-case, and may include medications to control blood pressure or surgery.