A cerebral or brain aneurysm is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel. A common location of cerebral aneurysms is on the arteries at the base of the brain, known as the Circle of Willis. Aneurysms may result from congenital defects, preexisting conditions such as high blood pressure and atherosclerosis (the buildup of fatty deposits in the arteries), or head trauma. Cerebral aneurysms occur more commonly in adults than in children and are slightly more common in women than in men, but they may occur at any age.

A small, unchanging aneurysm will produce no symptoms. Before a larger aneurysm ruptures, the individual may experience such symptoms as a sudden and usually severe headache, nausea, vision impairment, vomiting, and loss of consciousness, or the individual may be asymptomatic, experiencing no symptoms at all. Onset is usually sudden and without warning. Rupture of a cerebral aneurysm is dangerous and usually results in bleeding into the meninges or the brain itself, leading to a subarachnoid hemorrhage or intracranial hematoma, either of which constitutes a stroke. Rebleeding, hydrocephalus (the excessive accumulation of cerebrospinal fluid), vasospasm (spasm of the blood vessels), or multiple aneurysms may also occur. An unruptured cerebral aneurysm has a 4% chance of rupturing each year.

In outlining symptoms of ruptured cerebral aneurysm, it is useful to make use of the Hunt and Hess scale of subarachnoid hemorrhage severity:

• Grade 1: Asymptomatic; or minimal headache and slight nuchal rigidity. Approximate survival rate 70%.
• Grade 2: Moderate to severe headache; nuchal rigidity; no neurologic deficit except cranial nerve palsy. 60%.
• Grade 3: Drowsy; minimal neurologic deficit. 50%.
• Grade 4: Stuporous; moderate to severe hemiparesis; possibly early decerebrate rigidity and vegetative disturbances. 20%.
• Grade 5: Deep coma; decerebrate rigidity; moribund. 10%.

Emergency treatment for individuals with a ruptured cerebral aneurysm generally includes restoring deteriorating respiration and reducing intracranial pressure. Surgery is usually performed within the first three days to clip the ruptured aneurysm and reduce the risk of rebleeding. When aneurysms are discovered before rupture occurs, microcoil thrombosis or balloon embolization may be performed on patients for whom surgery is considered too risky. During these procedures, a thin, hollow tube (catheter) is inserted through an artery to travel up to the brain. Once the catheter reaches the aneurysm, tiny balloons or coils are used to block blood flow through the aneurysm. Other treatments may include bedrest, drug therapy, or hypertensive-hypervolemic therapy (which elevates blood pressure, increases blood volume, and thins the blood) to drive blood flow through and around blocked arteries and control vasospasm.

The prognosis for a patient with a ruptured cerebral aneurysm depends on the extent and location of the aneurysm, the person's age, general health, and neurological condition. Some individuals with a ruptured cerebral aneurysm die from the initial bleeding. Other individuals with cerebral aneurysm recover with little or no neurological deficit. However, estimates are, that of the 30,000 people per year in the United States who suffer a ruptured aneurysm, only 20% will be alive and well in one year's time. 20% will be alive but disabled, and 60% will have died.

See also: Stroke

The base text for this article was taken from the National Institute of Neurological Disorders and Stroke public domain resource at http://www.ninds.nih.gov/health_and_medical/disorders/ceraneur_doc.htm.