A cerebral aneurysm is a weak or thin spot on a blood vessel in the brain that balloons out and fills with blood.  A cerebral aneurysm can press on a nerve or surrounding tissue in the brain, and also leak or burst, which lets blood spill into surrounding tissues (called a hemorrhage). Cerebral aneurysms can occur at any age, although they are more common in adults than in children and are more common in women than in men. These aneurysms can occur anywhere in the brain. Some small aneurysms may not show signs and are usually detected during imaging tests for other medical conditions. The signs and symptoms of an unruptured cerebral aneurysm will partly depend on its size and rate of growth. A larger aneurysm that is steadily growing may produce symptoms such as numbness, pain above and behind the eye, and paralysis on one side of the face. Immediately after an aneurysm ruptures, an individual may experience such symptoms as a sudden and unusually severe headache, nausea, vision impairment, vomiting, and loss of consciousness.


Not all cerebral aneurysms require treatment. Small unruptured aneurysms that do not show symptoms should be monitored regularly. Treatment may be recommended for large or irregularly-shaped aneurysms or for those causing symptoms. Emergency treatment for individuals with a ruptured cerebral aneurysm may be required to restore deteriorating respiration and reduce abnormally high pressure within the brain.  Treatment is necessary to prevent the aneurysm from rupturing again. Treatment for unruptured and ruptured cerebral aneurysms include surgery to clip or fill the aneurysm, or to reduce its blood flow. Various medications may be prescribed to treat related symptoms or to reduce the risk of stroke.


The prognosis for a individual with a ruptured cerebral aneurysm depends on the location of the aneurysm, extent of bleeding or rebleeding, the person's age, general health, pre-existing neurological conditions, and time between rupture and medical attention. Early diagnosis and treatment are important. A burst cerebral aneurysm could be fatal or lead to hemorrhagic stroke, vasospasm (in which other blood vessels in the brain contract and limit blood flow), hydrocephalus, coma, or short-term and/or permanent brain damage. Recovery from treatment or rupture may take weeks to months. Steps to reduce the risk of aneurysm rupture include controlling bood pressure, stopping smoking and avoiding stimulant drugs. Approximately 25 percent of individuals whose cerebral aneurysm has ruptured do not survive the first 24 hours.


NINDS supports a broad range of basic and clinical research on cerebral aneurysms and other vascular lesions of the nervous system. NINDS funded the International Study of Unruptured Intracranial Aneurysms that guides medical decision-making based on size and location of aneurysms that do not show symptoms. Other research projects include genome-wide studies to identify genes or DNA sequences that may indicate families harboring one type of aneurysm may be at increased risk of another type. Among other research, scientists are studying chromosomes to identify aneurysm-related genes and developing new models to diagnose brain aneurysms based on the presence of molecules that can potentially tell whether there is a high chance of an aneurysm burst. Information from the National Library of Medicine’s MedlinePlus Brain Aneurysm