What Are Brain Aneurysms?

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What is a Brain (Cerebral) Aneurysm?

A cerebral aneurysm (also known as an intracranial or intra-cerebral 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.

How are Cerebral Aneurysms treated?

Not all cerebral aneurysms burst.  Some people 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; the individual'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 individual (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 person 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 individual 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 person's lifetime.

People 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 person 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.  Individuals 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 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 sponsored the International Study of Unruptured Intracranial Aneurysms, which included more than 4,000 people at 61 sites in the United States, Canada, and Europe.  The findings suggest that the risk of rupture for most very small aneurysms (less than 7 millimeters in size) is small.  The results also provide a more comprehensive look at these vascular defects and offer guidance to individuals and physicians facing the difficult decision about whether or not to treat an aneurysm surgically.

NINDS scientists are studying the effects of an experimental drug 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.

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 people with subarachnoid hemorrhage.  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 individuals 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 individuals with cerebral aneurysms.

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- Causes, symptoms, and diagnosis
                   o   Brain Aneurysms- Classification and prognosis

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