A cerebral aneurysm, or "intracranial aneurysm" is a weak or thin spot on a blood vessel in the brain that balloons out and fills with fluid. Most cerebral aneurysms are congenital, resulting from an inborn abnormality in an artery wall. Cerebral aneurysms are more common in people with genetic diseases, or certain circulatory diseases such as arterio-venous malformations. Other causes of aneurysms include trauma or injury to the head, high blood pressure, infection, tumors etc.