Brain Aneurysms: Classification and Prognosis

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A brain (cerebral) aneurysm is a weak or thin spot on a blood vessel in the brain that balloons out and fills with blood.

How are Cerebral Aneurysms classified?

There are three types of cerebral aneurysm.  A saccular aneurysm is a rounded or pouch-like sac of blood that is attached by a neck or stem to an artery or a branch of a blood vessel.  Also known as a berry aneurysm (because it resembles a berry hanging from a vine), this most common form of cerebral aneurysm is typically found on arteries at the base of the brain.  Saccular aneurysms occur most often in adults.  A lateral aneurysm appears as a bulge on one wall of the blood vessel, while a fusiform aneurysm is formed by the widening along all walls of the vessel.

Aneurysms are also classified by size.  Small aneurysms are less than 11 millimeters in diameter (about the size of a large pencil eraser), larger aneurysms are 11-25 millimeters (about the width of a dime), and giant aneurysms are greater than 25 millimeters in diameter (more than the width of a quarter).

Who is at risk?

Brain aneurysms can occur in anyone, at any age.  They are more common in adults than in children and slightly more common in women than in men.  People with certain inherited disorders are also at higher risk.

All cerebral aneurysms have the potential to rupture and cause bleeding within the brain.  The incidence of reported ruptured aneurysm is about 10 in every 100,000 persons per year (about 27,000 individuals per year in the U.S.), most commonly in people between ages 30 and 60 years.  Possible risk factors for rupture include hypertension, alcohol abuse, drug abuse (particularly cocaine), and smoking.  In addition, the condition and size of the aneurysm affects the risk of rupture.

What are the dangers?

Aneurysms may burst and bleed into the brain, causing serious complications, including hemorrhagic stroke, permanent nerve damage, or death.  Once it has burst, the aneurysm may burst again and bleed into the brain, and additional aneurysms may also occur.  More commonly, rupture may cause a subarachnoid hemorrhage - bleeding into the space between the skull bone and the brain.  A delayed but serious complication of subarachnoid hemorrhage is hydrocephalus, in which the excessive buildup of cerebrospinal fluid in the skull dilates fluid pathways called ventricles that can swell and press on the brain tissue.  Another delayed post-rupture complication is vasospasm, in which other blood vessels in the brain contract and limit blood flow to vital areas of the brain.  This reduced blood flow can cause stroke or tissue damage.

What is the prognosis?

An un-ruptured aneurysm may go unnoticed throughout a person's lifetime.  A burst aneurysm, however, may be fatal or could lead to hemorrhagic stroke, vasospasm (the leading cause of disability or death following a burst aneurysm), hydrocephalus, coma, or short-term and/or permanent brain damage.

The prognosis for persons whose aneurysm has burst is largely dependent on the age and general health of the individual, other preexisting neurological conditions, location of the aneurysm, extent of bleeding (and re-bleeding), and time between rupture and medical attention.  It is estimated that about 40 percent of individuals whose aneurysm has ruptured do not survive the first 24 hours; up to another 25 percent die from complications within 6 months.  People who experience subarachnoid hemorrhage may have permanent neurological damage.  Other individuals may recover with little or no neurological deficit.  Delayed complications from a burst aneurysm may include hydrocephalus and vasospasm.  Early diagnosis and treatment are important.

Individuals who receive treatment for an un-ruptured aneurysm generally require less rehabilitative therapy and recover more quickly than persons whose aneurysm has burst.  Recovery from treatment or rupture may take weeks to months.

Results of the International Subarachnoid Aneurysm Trial (ISAT), sponsored primarily by health ministries in the United Kingdom, France, and Canada and announced in October 2002, found that outcome for individuals who are treated with endovascular coiling may be superior in the short-term (1 year) to outcome for those whose aneurysm is treated with surgical clipping.  Long-term results of coiling procedures are unknown and investigators need to conduct more research on this topic, since some aneurysms can recur after coiling.  Individuals may want to consult a specialist in both endovascular and surgical repair of aneurysms, to help provide greater understanding of treatment options.

Source: Information provided courtesy of the National Institute of Neurological Disorders and Stroke (NINDS), a division of the National Institutes of Health (NIH).

NINDS health-related material is provided for information purposes only and does not necessarily represent endorsement by or an official position of the National Institute of Neurological Disorders and Stroke or any other Federal agency. Advice on the treatment or care of an individual patient should be obtained through consultation with a physician who has examined that patient or is familiar with that patient's medical history.

• See also:

                   o   Brain Aneurysms- Overview
                   o   Brain Aneurysms- Causes, symptoms, and diagnosis

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