Brain aneurysm: An aneurysm of a blood vessel in the brain, usually due to a defect in the vessel at birth or from high blood pressure. Rupture of the aneurysm causes a sudden severe headache, often with nausea, vomiting, decreased consciousness, and can be life threatening.
Quick GuideDementia, Alzheimer's Disease, and Aging Brains
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Last Editorial Review: 3/30/2012