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.
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.
 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
 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:
Information also is available
from the following organizations:
Brain Aneurysm Foundation
Stroke Association: A Division of American Heart Association
Tel: 1-888-4STROKE (478-7653)
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.
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