Cerebral Aneurysm

Definition

A cerebral aneurysm occurs at a weak point in the wall of a blood vessel (artery) that supplies blood to the brain. Because of the flaw, the artery wall bulges outward and fills with blood. This bulge is called an aneurysm. An aneurysm can rupture, spilling blood into the surrounding body tissue. A ruptured cerebral aneurysm can cause permanent brain damage, disability, or death.

Description

A cerebral aneurysm can occur anywhere in the brain. Aneurysms can have several shapes. The saccular aneurysm, once called a berry aneurysm, resembles a piece of fruit dangling from a branch. Saccular aneurysms are usually found at a branch in the blood vessel where they balloon out by a thin neck. Saccular cerebral aneurysms most often occur at the branch points of large arteries at the base of the brain. Aneurysms may also take the form of a bulge in one wall of the artery—a lateral aneurysm—or a widening of the entire artery—a fusiform aneurysm.

The greatest danger of aneurysms is rupture. Approximately 50-75% of stricken people survive an aneurysmal rupture. A ruptured aneurysm spills blood into the brain or into the fluid-filled area that surrounds the brain tissue. Bleeding into this area, called the subarachnoid space, is referred to as subarachnoid hemorrhage (SAH). About 25,000 people suffer a SAH each year. It is estimated that people with unruptured aneurysm have an annual 1-2% risk of hemorrhage. Under age 40, more men experience SAH. After age 40, more women than men are affected.

Most people who have suffered a SAH from a ruptured aneurysm did not know that the aneurysm even existed. Based on autopsy studies, medical researchers estimate that 1-5% of the population has some type of cerebral aneurysm. Aneurysms rarely occur in the very young or the very old; about 60% of aneurysms are diagnosed in people between ages 40 and 65.

Some aneurysms may have a genetic link and run in families. The genetic link has not been completely proven and a pattern of inheritance has not been determined. Some studies seem to show that first-degree relatives of people who suffered aneurysmal SAH are more likely to have aneurysms themselves. These studies reported that such immediate family members were four times more likely to have aneurysms than the general population. Other studies do not confirm these findings. Better evidence links aneurysms to certain rare diseases of the connective tissue. These diseases include Marfan syndrome, pseudoxanthoma elasticum, Ehlers-Danlos syndrome, and fibromuscular dysplasia. Polycystic kidney disease is also associated with cerebral aneurysms.

These diseases are also associated with an increased risk of aneurysmal rupture. Certain other conditions raise the risk of rupture, too. Most aneurysms that rupture are a half-inch or larger in diameter. Size is not the only factor, however, because smaller aneurysms also rupture. Cigarette smoking, excessive alcohol consumption, and recreational drug use (for example, use of cocaine ) have been linked with an increased risk. The role, if any, of high blood pressure has not been determined. Some studies have implicated high blood pressure in aneurysm formation and rupture, but people with normal blood pressure also experience aneurysms and SAHs. High blood pressure may be a risk factor but not the most important one. Pregnancy, labor, and delivery also seem to increase the possibility that an aneurysm might rupture, but not all doctors agree. Physical exertion and use of oral contraceptives are not suspected causes for aneurysmal rupture.

Causes and symptoms

Cerebral aneurysms can be caused by brain trauma, infection, hardening of the arteries (athero-sclerosis ), or abnormal rapid cell growth (neoplastic disease), but most seem to arise from a congenital, or developmental, defect. These congenital aneurysms occur more frequently in women. Whatever the cause may be, the inner wall of the blood vessel is abnormally thin and the pressure of the blood flow causes an aneurysm to form.

Most aneurysms go unnoticed until they rupture. However, 10-15% of unruptured cerebral aneurysms are found because of their size or their location. Common warning signs include symptoms that affect only one eye, such as an enlarged pupil, a drooping eyelid, or pain above or behind the eye. Other symptoms are a localized headache, unsteady gait, a temporary problem with sight, double vision, or numbness in the face.

Some aneurysms bleed occasionally without rupturing. Symptoms of such an aneurysm develop gradually. The symptoms include headache, nausea, vomiting, neck pain, black-outs, ringing in the ears, dizziness, or seeing spots.

Eighty to ninety percent of aneurysms are not diagnosed until after they have ruptured. Rupture is not always a sudden event. Nearly 50% of patients who have aneurysmal SAHs also experience "the warning leak phenomenon." Persons with warning leak symptoms have sudden, atypical headaches that occur days or weeks before the actual rupture. These headaches are referred to as sentinel headaches. Nausea, vomiting, and dizziness may accompany sentinel headaches. Unfortunately, these symptoms can be confused with tension headaches or migraines, and treatment can be delayed until rupture occurs.

When an aneurysm ruptures, most victims experience a sudden, extremely severe headache. This headache is typically described as the worst headache of the victim's life. Nausea and vomiting commonly accompany the headache. The person may experience a short loss of consciousness or prolonged coma. Other common signs of a SAH include a stiff neck, fever, and a sensitivity to light. About 25% of victims experience neurological problems linked to specific areas of the brain, swelling of the brain due to fluid accumulation (hydrocephalus ), or seizure.

Diagnosis

Based on the clinical symptoms, a doctor will run several tests to confirm an aneurysm or an SAH. A computed tomography scan (CT) of the head is the initial procedure. A magnetic resonance imaging test (MRI) may be done instead of a CT scan. MRI, however, is not as sensitive as CT for detecting subarachnoid blood. A CT scan can determine whether there has been a hemorrhage and can assist in pinpointing the location of the aneurysm. The scan is most useful when it is done within 72 hours of the rupture. Later scans may miss the signs of hemorrhage.

If the CT scan is negative for a hemorrhage or provides an unclear diagnosis, the doctor will order a cerebrospinal fluid (CSF) analysis, also called a lumbar puncture. In this procedure, a small amount of cerebrospinal fluid is removed from the lower back and examined for traces of blood and blood-breakdown products. If this test is positive, cerebral angiography is used to map the brain's blood vessels and the damaged area. The angiography is done to pinpoint the aneurysm's location. About 15% of people who experience SAH have more than one aneurysm. For this reason, angiography should include both the common carotid artery that feeds the front of the brain and the vertebral artery that feeds the base of the brain. Occasionally, the angiography fails to find the aneurysm and must be repeated. If seizures occur, electroencephalography (EEG) may be used to measure the electrical activity of the brain.

Treatment

Unruptured aneurysm

If an aneurysm has not ruptured and is not causing any symptoms, it may be left untreated. Because there is a 1-2% chance of rupture per year, the cumulative risk over a number of years may justify surgical treatment. However, if the aneurysm is small or in a place that would be difficult to reach, or if the person who has the aneurysm is in poor health, the surgical treatment may be a greater risk than the aneurysm. Risk of rupture is higher for people who have more than one aneurysm. Unruptured aneurysm would probably be treated with a surgical procedure called the clip ligation, as described below.

Ruptured aneurysm

The primary treatment for a ruptured aneurysm involves stabilizing the victim's condition, treating the immediate symptoms, and promptly assessing further treatment options, especially surgical procedures. The patient may require mechanical ventilation, oxygen, and fluids. Medications may be given to prevent major secondary complications such as seizures, rebleeding, and vasospasm (narrowing of the affected blood vessel). Vasospasm decreases blood flow to the brain and causes the death of nerve cells. A drug such as nimodipine (Nimotop) may help prevent vasospasm by relaxing the smooth muscle tissue of the arteries. Even with treatment, however, vasospasm may cause stroke or death.

To prevent further hemorrhage from the aneurysm, it must be removed from circulation. In general, surgical procedures should be performed as soon as possible to prevent rebleeding. The chances that aneurysm will rebleed are greatest in the first 24 hours, and vasospasm usually does not occur until 72 hours or more after rupture. If the patient is in poor condition or if there is vasospasm or other complication, surgical procedures may be delayed. The preferred surgical method is a clip ligation in which a clip is placed around the base of the aneurysm to block it off from circulation. Surgical coating, wrapping, or trapping of the aneurysm may also be performed. These procedures do not completely remove the aneurysm from circulation, however, and there is some risk that it may rebleed in the future. Newer techniques that look promising include balloon embolization, a procedure that blocks the aneurysm with an inflatable membrane introduced by means of a catheter inserted through the artery.

Prognosis

An unruptured aneurysm may not cause any symptoms over an entire lifetime. Surgical clip ligation will ensure that it won't rupture, but it may be better to leave the aneurysm alone in some cases. Familial cerebral aneurysms may rupture earlier than those without a genetic link.

KEY TERMS

Congenital— Existing at birth.

Ehlers-Danlos syndrome— A rare inheritable disease of the connective tissue marked by very elastic skin, very loose joints, and very fragile body tissue.

Embolization— A technique to stop or prevent hemorrhage by introducing a foreign mass, such as an air-filled membrane (balloon), into a blood vessel to block the flow of blood.

Fibromuscular dysplasia— A disorder that causes unexplained narrowing of arteries and high blood pressure.

Magnetic resonance angiography— A noninvasive diagnostic technique that uses radio waves to map the internal anatomy of the blood vessels.

Marfan syndrome— An inheritable disorder that affects the skeleton, joints, and blood vessels. Major indicators are excessively long arms and legs, lax joints, and vascular defects.

Nimodipine (Nimotop)— A calcium-channel blocker, that is, a drug that relaxes arterial smooth muscle by slowing the movement of calcium across cell walls.

Polycystic kidney disease— An abnormal condition in which the kidneys are enlarged and contain many cysts.

Pseudoxanthoma elasticum— A hereditary disorder of the connective, or elastic, tissue marked by premature aging and breakdown of the skin and degeneration of the arteries that leads to hemorrhages.

Subarachnoid hemorrhage (SAH)— Loss of blood into the subarachnoid space, the fluid-filled area that surrounds the brain tissue.

Vasospasm— Narrowing of a blood vessel caused by a spasm of the smooth muscle of the vessel wall.

The outlook is not as good for a person who suffers a ruptured aneurysm. Fifteen to twenty-five percent of people who experience a ruptured aneurysm do not survive. An additional 25-50% die as a result of complications associated with the hemorrhage. Of the survivors, 15-50% suffer permanent brain damage and disability. These conditions are caused by the death of nerve cells. Nerve cells can be destroyed by the hemorrhage itself or by complications from the hemorrhage, such as vasospasm or hydrocephalus. Hydrocephalus, a dilatation (expansion) of the fluid-filled cavity surrounding the brain, occurs in about 15% of cases. Immediate medical treatment is vital to prevent further complications and brain damage in those who survive the initial rupture. Patients who survive SAH and aneurysm clipping are unlikely to die from events related to SAH.

Prevention

There are no known methods to prevent an aneurysm from forming. If an aneurysm is discovered before it ruptures, it may be surgically removed. CT or MRI angiography may be recommended for relatives of patients with familial cerebral aneurysms.

Resources

ORGANIZATIONS

Brain Aneurysm Foundation, Inc. 66 Canal St., Boston, MA 02114. (617) 723-3870. 〈http://neurosurgery.mgh.harvard.edu/baf〉.

OTHER

Bernadini, Gary L. "Intracerebral Aneurysms." Columbia University Health Sciences Page. 〈http://cpmcnet.columbia.edu〉.

"The Brain Aneurysm Report." Neurosurgical Service Page. Harvard Medical School. 〈http://neurosurgery.mgh.harvard.edu/abta/primer.htm〉.

CEREBRAL ANEURYSM

DEFINITION

A cerebral aneurysm (pronounced an-yuh-RIH-zim) occurs at a weak spot in an artery that supplies blood to the brain. Once weakened, the artery wall bulges outward and fills with blood. This bulge is called an aneurysm. An aneurysm can burst, spilling blood into the brain. When this happens, permanent brain damage, disability, or death may occur.

DESCRIPTION

Arteries are blood vessels that carry blood from the heart to other parts of the body. For a variety of reasons, weak spots sometimes develop in the walls of an artery. When that happens, an aneurysm develops. An aneurysm in the brain is one of the most dangerous types.

The greatest danger of an aneurysm is rupture. A ruptured aneurysm in the brain allows blood to flow into the surrounding area. Blood may also flow into the area that surrounds brain tissue. This event is called a subarachnoid hemorrhage (SAH; pronounced sub-uh-RAK-noid hem-uh-RIJ).

About 1 percent of individuals with an aneurysm are at risk for a hemorrhage. Under age forty, more men tend to experience an SAH. After age forty, more women than men are affected. There are seldom any warning signs of an SAH. Most people who have a hemorrhage never knew they had an aneurysm. Based on autopsies (medical studies of dead bodies), 1 to 5 percent of the total population has had some type of cerebral aneurysm.

CAUSES

Most cases of cerebral aneurysm are caused by congenital factors. Congenital means that the person was born with the defect. The person has artery walls that are thinner than normal in some places. It is in these regions that aneurysms develop. Aneurysms may be caused by other factors, as well. These factors include injury to the brain, infection, hardening of the arteries (see atherosclerosis entry), or abnormally rapid growth of brain cells.

SYMPTOMS

Most aneurysms go unnoticed until they rupture. In about 10 to 15 percent of cases, however, there are symptoms. Common warning signs include an enlarged pupil in one eye, a drooping eyelid, or pain above or behind the eye. Other symptoms include a headache in one specific part of the head, difficulty in walking, double vision, or numbness in the face.

Cerebral Aneurysm: Words to Know

Angiography:

A procedure in which a dye is pumped into a person's blood vessels so that X–ray photographs can show the structure of organs and tissues more clearly.

Atherosclerosis:

Hardening of the arteries.

Cerebrospinal fluid:

A clear liquid that bathes the brain and spinal column.

Computed tomography (CT) scan:

A procedure by which X rays are directed at a patient's body from various angles and the set of photographs thus obtained assembled by a computer program.

Computerized axial tomography (CAT) scan:

Another name for a computed tomography (CT) scan.

Congenital disorder:

A medical condition that is present at birth.

Lumbar puncture:

A procedure in which a long, thin needle is used to withdraw cerebrospinal fluid from a patient's spine.

Subarachnoid hemorrhage (SAH):

Loss of blood into the subarachnoid space, the fluid-filled area that surrounds brain tissue.

Some aneurysms bleed without rupturing. In such cases, symptoms may develop gradually. They include headache, nausea, vomiting, neck pain, blackouts, ringing in the ears, dizziness, or seeing spots.

Aneurysms do not always rupture suddenly. Sometimes, they begin to ooze blood slowly. When this happens, patients may experience certain warning signs. These warning signs include headaches, nausea, vomiting, and dizziness. Unfortunately, these symptoms are easily confused with ordinary tension headaches. An individual may not realize that these are symptoms of a more serious problem.

When an aneurysm ruptures, most patients experience a sudden, extremely severe headache. The headache is often described as the worst the patient has ever had. The headache is often accompanied by nausea, vomiting, and loss of consciousness. The patient may also experience a stiff neck, fever, and unusual sensitivity to light. About one-quarter of all patients experience problems that affect the nervous system, including swelling of the brain.

DIAGNOSIS

The symptoms described may prompt a doctor to order a series of tests for a cerebral aneurysm. The most reliable test is a computed tomography

(CT) scan. In a CT scan, X rays are projected through the brain at various angles. These X rays produce photographs of the brain from different directions. A computer program is then used to combine the pictures, which produces a broad, overall view of the brain. CT scans are also sometimes called computerized axial tomography (CAT) scans.

A CT scan is usually able to determine whether or not an aneurysm exists. It is also able to pinpoint the region of the brain in which the rupture has occurred. To get the clearest result, the scan must usually be done within seventy-two hours after rupture.

If questions remain after a CT scan, follow-up tests might be run. One such test is a lumbar puncture, or spinal tap. In a lumbar puncture, a long, thin needle is used to remove cerebrospinal fluid (CF, liquid surrounding the brain and spinal column) from a patient's spine. The fluid is studied for certain characteristic materials formed when blood products are released in the brain.

Another follow-up test is a cerebral angiography (pronounced an-gee-AH-graffee). Cerebral angiography is a procedure in which a dye is injected into the blood. The dye is carried throughout the body, including to the brain. An X ray is then taken of the brain. The dye shows the presence of any abnormal structures in blood vessels.

TREATMENT

If an aneurysm has not ruptured, it may be left untreated. A person with an aneurysm has a 1 percent chance of having a rupture each year. As time goes on, a doctor may eventually decide to remove an aneurysm surgically. But the surgery may be more risky than leaving the aneurysm in place and monitoring any changes that may occur in its shape and size.

Once an aneurysm ruptures, the first step is to save the patient's life. Left untreated, a ruptured aneurysm can cause death in a short period of time. Patients may require both oxygen and fluids to remain stable. Medications may be needed to keep damaged blood vessels from collapsing. A drug known as nimodipine (pronounced ni-MO-dih-peen, trade name Nimotop) is often used for this purpose.

If the patient survives the rupture of an aneurysm, surgery is usually necessary. The purpose of the surgery is to close off the aneurysm and prevent it from further bleeding. In one approach, a clip is placed around the base of the aneurysm. The clip usually solves the problem for a while. However, the aneurysm may break loose again later, close to the point where the clip was placed.

PROGNOSIS

An unruptured aneurysm may not cause any symptoms over an entire lifetime. Surgical procedures are available for dealing with the aneurysm, but the risk from surgery may be at least as great as that from the aneurysm itself. The prognosis for people who experience a ruptured aneurysm is not good. About 15 to 25 percent of those who experience a rupture do not survive the event. An additional 25 to 50 percent survive the immediate episode, but die of complications caused by bleeding in the brain. Of those who do survive, about 15 to 50 percent suffer permanent brain damage or physical disability.

PREVENTION

There are no known methods for preventing the formation of an aneurysm. If an aneurysm is discovered before it ruptures, it may be removed surgically. Some doctors recommend CT scans or angiograms for relatives of patients who have had aneurysms.

FOR MORE INFORMATION

Organizations

The Brain Aneurysm Foundation, Inc. 66 Canal Street, Boston, MA 02114. (617) 723–3870. http://neurosurgery.mgh.harvard.edu/baf.

Web sites

Aneurysm and AVM Support Page. [Online] http://www.westga.edu.~wmaples/aneurysm.html (accessed on October 13, 1999).

berry aneurysm (b'e-ri) n. see aneurysm.