What is a cerebral aneurysm?
A cerebral aneurysm (also known as an intracranial or
intracerebral aneurysm) is a weak or thin spot on a blood vessel in the brain that
balloons out and fills with blood. The bulging aneurysm can put pressure on a
nerve or surrounding brain tissue. It may also leak or rupture, spilling blood
into the surrounding tissue (called a hemorrhage). Some cerebral aneurysms,
particularly those that are very small, do not bleed or cause other problems.
Cerebral aneurysms can occur anywhere in the brain, but most are located along
a loop of arteries that run between the underside of the brain and the base of
the skull.
What causes a cerebral aneurysm?
Most cerebral aneurysms are congenital, resulting from an inborn abnormality in
an artery wall. Cerebral aneurysms are also more common in people with certain
genetic diseases, such as connective tissue disorders and polycystic kidney
disease, and certain circulatory disorders, such as arteriovenous
malformations.[1]
Other causes include trauma or injury to the head,
high blood pressure, infection, tumors, atherosclerosis (a blood vessel disease
in which fats build up on the inside of artery walls) and other diseases of the
vascular system, cigarette smoking, and drug abuse. Some investigators have
speculated that oral contraceptives may increase the risk of developing
aneurysms.
Aneurysms that result from an infection in the
arterial wall are called mycotic aneurysms. Cancer-related aneurysms are often
associated with primary or metastatic tumors of the head and neck. Drug abuse,
particularly the habitual use of cocaine, can inflame blood vessels and lead to
the development of brain aneurysms.
[1] A congenital malformation in which a snarled
tangle of arteries and veins in the brain disrupts blood flow.
How are 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 standard 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 patients
per year in the
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 rebleed 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
postrupture 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 are the symptoms?
Most cerebral aneurysms do not show symptoms until they either become very
large or burst. Small, unchanging aneurysms generally will not produce
symptoms, whereas a larger aneurysm that is steadily growing may press on tissues
and nerves. Symptoms may include pain above and behind the eye; numbness,
weakness, or paralysis on one side of the face; dilated pupils; and vision
changes. When an aneurysm hemorrhages, an individual may experience a sudden
and extremely severe headache, double vision, nausea, vomiting, stiff neck,
and/or loss of consciousness. Patients usually describe the headache as
“the worst headache of my life” and it is generally different in
severity and intensity from other headaches patients may experience. “Sentinel”
or warning headaches may result from an aneurysm that leaks for days to weeks
prior to rupture. Only a minority of patients have a sentinel headache prior to
aneurysm rupture.
Other signs that a cerebral aneurysm has burst include
nausea and vomiting associated with a severe headache, a drooping eyelid,
sensitivity to light, and change in mental status or level of awareness. Some
individuals may have seizures. Individuals may lose consciousness briefly or go
into prolonged coma. People experiencing this “worst headache,”
especially when it is combined with any other symptoms, should seek immediate
medical attention.
How are cerebral aneurysms diagnosed?
Most cerebral aneurysms go unnoticed until they rupture or are detected by
brain imaging that may have been obtained for another condition. Several
diagnostic methods are available to provide information about the aneurysm and
the best form of treatment. The tests are usually obtained after a subarachnoid
hemorrhage, to confirm the diagnosis of an aneurysm.
Angiography is a dye test used to analyze the arteries
or veins. An intracerebral angiogram can detect the degree of narrowing or
obstruction of an artery or blood vessel in the brain, head, or neck, and can
identify changes in an artery or vein such as a weak spot like an aneurysm. It
is used to diagnose stroke and to precisely determine the location, size, and
shape of a brain tumor, aneurysm, or blood vessel that has bled. This test is
usually performed in a hospital angiography suite. Following the injection of a
local anesthetic, a flexible catheter is inserted into an artery and threaded
through the body to the affected artery. A small amount of contrast dye (one
that is highlighted on x-rays) is released into the bloodstream and allowed to travel
into the head and neck. A series of x-rays is taken and changes, if present,
are noted.
Computed tomography (CT) of the head is a fast,
painless, noninvasive diagnostic tool that can reveal the presence of a
cerebral aneurysm and determine, for those aneurysms that have burst, if blood
has leaked into the brain. This is often the first diagnostic procedure ordered
by a physician following suspected rupture. X-rays of the head are processed by
a computer as two-dimensional cross-sectional images, or “slices,”
of the brain and skull. Occasionally a contrast dye is injected into the
bloodstream prior to scanning. This process, called CT angiography, produces
sharper, more detailed images of blood flow in the brain arteries. CT is
usually conducted at a testing facility or hospital outpatient setting.
Magnetic resonance imaging (MRI) uses
computer-generated radio waves and a powerful magnetic field to produce
detailed images of the brain and other body structures. Magnetic resonance
angiography (MRA) produces more detailed images of blood vessels. The images
may be seen as either three-dimensional pictures or two-dimensional
cross-slices of the brain and vessels. These painless, noninvasive procedures
can show the size and shape of an unruptured aneurysm and can detect bleeding
in the brain.
Cerebrospinal fluid analysis may be ordered if a
ruptured aneurysm is suspected. Following application of a local anesthetic, a
small amount of this fluid (which protects the brain and spinal cord) is
removed from the subarachnoid space—located between the spinal cord and
the membranes that surround it—by surgical needle and tested to detect
any bleeding or brain hemorrhage. In patients with suspected subarachnoid
hemorrhage, this procedure is usually done in a hospital.
How are cerebral aneurysms treated?
Not all cerebral aneurysms burst. Some patients with very small aneurysms may
be monitored to detect any growth or onset of symptoms and to ensure aggressive
treatment of coexisting medical problems and risk factors. Each case is unique,
and considerations for treating an unruptured aneurysm include the type, size,
and location of the aneurysm; risk of rupture; patient’s age, health, and
personal and family medical history; and risk of treatment.
Two surgical options are available for treating
cerebral aneurysms, both of which carry some risk to the patient (such as
possible damage to other blood vessels, the potential for aneurysm recurrence
and rebleeding, and the risk of post-operative stroke).
Microvascular clipping involves cutting off the flow
of blood to the aneurysm. Under anesthesia, a section of the skull is removed
and the aneurysm is located. The neurosurgeon uses a microscope to isolate the
blood vessel that feeds the aneurysm and places a small, metal, clothespin-like
clip on the aneurysm’s neck, halting its blood supply. The clip remains
in the patient and prevents the risk of future bleeding. The piece of the skull
is then replaced and the scalp is closed. Clipping has been shown to be highly
effective, depending on the location, shape, and size of the aneurysm. In
general, aneurysms that are completely clipped surgically do not return.
A related procedure is an occlusion, in which the
surgeon clamps off (occludes) the entire artery that leads to the aneurysm.
This procedure is often performed when the aneurysm has damaged the artery. An
occlusion is sometimes accompanied by a bypass, in which a small blood vessel
is surgically grafted to the brain artery, rerouting the flow of blood away
from the section of the damaged artery.
Endovascular embolization is an alternative to
surgery. Once the patient has been anesthetized, the doctor inserts a hollow
plastic tube (a catheter) into an artery (usually in the groin) and threads it,
using angiography, through the body to the site of the aneurysm. Using a guide
wire, detachable coils (spirals of platinum wire) or small latex balloons are
passed through the catheter and released into the aneurysm. The coils or
balloons fill the aneurysm, block it from circulation, and cause the blood to
clot, which effectively destroys the aneurysm. The procedure may need to be
performed more than once during the patient’s lifetime.
Patients who receive treatment for aneurysm must
remain in bed until the bleeding stops. Underlying conditions, such as high
blood pressure, should be treated. Other treatment for cerebral aneurysm is
symptomatic and may include anticonvulsants to prevent seizures and analgesics
to treat headache. Vasospasm can be treated with calcium channel-blocking drugs
and sedatives may be ordered if the patient is restless. A shunt may be
surgically inserted into a ventricle several months following rupture if the
buildup of cerebrospinal fluid is causing harmful pressure on surrounding
tissue. Patients who have suffered a subarachnoid hemorrhage often need
rehabilitative, speech, and occupational therapy to regain lost function and
learn to cope with any permanent disability.
Can cerebral aneurysms be prevented?
There are no known ways to prevent a cerebral aneurysm from forming. People
with a diagnosed brain aneurysm should carefully control high blood pressure,
stop smoking, and avoid cocaine use or other stimulant drugs. They should also
consult with a doctor about the benefits and risks of taking aspirin or other
drugs that thin the blood. Women should check with their doctors about the use
of oral contraceptives.
What is the prognosis?
An unruptured 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 rebleeding), and time between rupture and medical attention. It
is estimated that about 40 percent of patients whose aneurysm has ruptured do
not survive the first 24 hours; up to another 25 percent die from complications
within 6 months. Patients 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 vapospasm. Early diagnosis and treatment are important.
Individuals who receive treatment for an unruptured
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
patients who are treated with endovascular coiling may be superior in the
short-term (1 year) to outcome for patients 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. Before treatment patients may want to consult with a
specialist in both endovascular and surgical repair of aneurysms, to help
provide greater understanding of treatment options. (The American Association
of Neurological Surgeons notes that most of the centers involved in the ISAT
were in Europe [primarily in
[2] American Association of Neurological
Surgeons/Congress of Neurological Surgeons, “Position Statement on the
International Subarachnoid Aneurysm Trial (ISAT),” November 5, 2002.
What research is being done?
The National Institute of Neurological Disorders and Stroke (NINDS), a
component of the National Institutes of Health (NIH) within the U.S. Department
of Health and Human Services, is the nation’s primary supporter of
research on the brain and nervous system. As part of its mission, the NINDS
conducts research on intracranial aneurysms and other vascular lesions of the
nervous system and supports studies through grants to medical institutions
across the country.
The NINDS recently sponsored the International Study
of Unruptured Intracranial Aneurysms, which included more than 4,000 patients
at 61 sites in the
NINDS scientists are studying the effects of an
experimental drug (proliNO) in treating vasospasm that occurs following rupture
of a cerebral aneurysm. The drug, developed at the NIH, delivers nitric oxide
to the arteries and has been shown to reverse and prevent brain artery spasms
in animals. This NINDS clinical trial is the first study of the drug in humans.
Other scientists hope to improve diagnosis and
prediction of cerebral vasospasm by developing antibodies to molecules known to
cause vasospasm. These molecules can be detected in the cerebrospinal fluid of
subarachnoid hemorrhage patients. An additional study will compare standard
treatment for subarachnoid hemorrhage to standard treatment plus transluminal
balloon angioplasty immediately after severe bleeding. Transluminal balloon
angioplasty involves the insertion, via catheter, of a deflated balloon through
the affected artery and into the clot. The balloon is inflated to widen the
artery and restore blood flow (the deflated balloon and catheter are then
withdrawn).
Researchers are building a new, noninvasive,
high-resolution x-ray detector system that can be used to guide the placement
of stents (small tube-like devices that keep blood vessels open) used to modify
blood flow during treatment for brain aneurysms.
Several groups of NINDS-funded researchers are
conducting genetic linkage studies to identify risk factors for familial
intracranial aneurysm and/or subarachnoid hemorrhage. One study hopes to
establish patterns of inheritance in patients of different ethnic backgrounds.
Another project is aimed at targeting and providing prevention and treatment
strategies for persons who are genetically at high risk for the development of
brain aneurysms. And other investigators will establish a blood and tissue
sampling bank for genetic linkage and molecular analyses.
Scientists are investigating the use of intraoperative
hypothermia during microclip surgery as a means to improve the rate of recovery
of cognitive functions and to reduce early and postoperative complications and
neurological damage. Other studies are investigating ways to improve or replace
the coils used in endovascular embolization.
Additional research being funded by the NINDS includes
the development of a new animal model of human saccular aneurysm, a new method
for tissue processing that should allow routine evaluation of the biological
response to implantation of occlusion devices, and a computer simulation model
to evaluate the outcomes of neurosurgery in patients with cerebral aneurysms.
Where can I get more information?
For more
information on neurological disorders or research programs funded by the
National Institute of Neurological Disorders and Stroke, contact the
Institute's Brain Resources and Information Network (BRAIN) at:
BRAIN
(800)
352-9424
http://www.ninds.nih.gov
Information also is available
from the following organizations:
Brain Aneurysm Foundation
information@bafound.org
http://www.bafound.org
Tel: 617-723-3870
Fax:
617-723-8672
American
Stroke Association: A Division of American Heart Association
strokeassociation@heart.org
http://www.strokeassociation.org
Tel:
1-888-4STROKE (478-7653)
Fax:
214-706-5231
American
Association of Neurological Surgeons
info@aans.org
http://www.aans.org
Tel:
847-378-0500/888-566-AANS (2267)
Fax:
847-378-0600
This information was developed by National Institute of
Neurological Disorders and Stroke, National Institutes of Health.
National Institute of
Neurological Disorders and Stroke. Cerebral Aneurysm Fact Sheet. Available at: http://www.ninds.nih.gov/disorders/cerebral_aneurysm/detail_cerebral_aneurysm.htm.
Last accessed April 25, 2005.
The information in this document is for general educational purposes only. It is not intended to substitute for personalized professional advice. Although the information was obtained from sources believed to be reliable, MedLink Corporation, its representatives, and the providers of the information do not guarantee its accuracy and disclaim responsibility for adverse consequences resulting from its use. For further information, consult a physician and the organization referred to herein.
