A cerebral aneurysm is a weakened area in the wall of an artery in the brain that bulges or balloons out. The expanded portion of the vessel (the aneurysm) may push against surrounding nerves, causing symptoms. There is the risk that the aneurysm may rupture, causing bleeding into and around the brain (hemorrhage). This is a very serious medical condition that requires immediate treatment.

The majority of cerebral aneurysms do not cause symptoms until they become large or rupture. Symptoms may include pain around the eye area, numbness or weakness particularly on one side of the face and vision changes. If an aneurysm bursts, patients may experience a sudden, extremely severe headache, nausea and changes in mental status.

Most cerebral aneurysms are the result of a congenital abnormality, meaning the defect is present at birth. They are also more common in individuals with certain genetic diseases, and circulatory disorders. Some aneurysms develop as the result of head trauma, infection or drug abuse. There are no known ways to prevent the formation of an aneurysm.

It is estimated that between 10 and 15 million Americans have cerebral aneurysms. Of these, about 30,000 people experience an aneurysm rupture every year. Thus, most aneurysms do not rupture. They may remain small and stable and may not cause clear symptoms. Because of this, most aneurysms are not detected until they grow and rupture, or unless they are noticed as part of a screening for another condition. 

Several tests may be used to diagnose a cerebral aneurysm, however, they are often administered after a rupture. Angiography, CAT scan or MRI may be used to confirm the aneurysm, assess the extent of damage from the hemorrhage and help plan treatment.

The decision to treat an unruptured aneurysm with no symptoms is somewhat controversial. Physicians must weigh the patient’s overall health and risk of treatment against the chances of rupture. Factors taken into consideration include the age of the patient, the size and location of the aneurysm, the risk of rupture and the patient’s medical history. This decision is made on an individual basis and people are urged to get a second opinion if they are concerned with their initial evaluation and treatment plan.

If treatment is chosen, physicians may recommend surgery that involves clipping or clamping off the affected artery. Surgeons also may choose a procedure that places a coil into the aneurysm. The type of surgery to repair the aneurysm is based on a number of factors.

The prognosis varies greatly among individuals who develop a ruptured aneurysm. The major factors that affect a patient’s outlook include the location of the aneurysm, the extent of damage from the hemorrhage, the time between the rupture and medical attention and other health conditions.

A cerebral aneurysm is the dilation, bulging or ballooning out of part of the wall of a cerebral artery. The cerebral arteries are two of the main blood vessels that carry oxygen-rich blood to the brain. Most aneurysms do not cause symptoms, but there is a risk that blood will leak into the surrounding area, causing such symptoms as headaches and vision problems. Such bleeding may also signal that an aneurysm rupture is about to occur. A rupture is a serious medical event that results in a subarachnoid hemorrhage (SAH).

An SAH is a kind of hemorrhagic stroke that involves bleeding into the area around the brain. Hemorrhagic strokes account for about 20 percent of total strokes, with SAH accounting for half of them. The remaining 10 percent of hemorrhagic strokes are caused by intracranial hemorrhage, which is closely associated with ruptures in blood vessels due to high blood pressure (hypertension) as well as other causes.

A SAH is a medical emergency. It is estimated that 10 percent of patients with SAH do not survive to reach the hospital, and about 40 percent do not survive the first 24 hours. In addition, another 25 percent of those who suffer a ruptured aneurysm die from complications within six months.

Those who survive a ruptured aneurysm face the risk of having neurological damage, including problems with cognitive function, speech, vision and motor impairment. The extent of damage varies greatly depending on the location of the aneurysm and the extent of bleeding.

Those who survive a ruptured aneurysm are also initially at increased risk of developing abnormal heart rhythms (arrhythmias), vasospasms of the cerebral arteries and subsequent fluid in the brain (hydrocephalus). There is also a significant danger that the aneurysm may start bleeding again.

Because most aneurysms are relatively small and do not have symptoms, they are difficult to detect. In many cases, an aneurysm is not detected until it becomes large and ruptures, unless it is found during a test for another condition. If a pre-rupture aneurysm is detected, the physician must decide how to progress. Treatment may involve surgery or less-invasive approaches that block the aneurysm. Although each case is different, the main factor driving the decision is the risk of an aneurysm rupture.

In general, the main predictor of whether or not an aneurysm will rupture is its size. Studies have shown that aneurysms that are larger than 7 millimeters (slightly less than half an inch) are at greater risk of rupture. Any aneurysm less than 11 millimeters (almost half an inch) is classified as small. Large aneurysms measure between 11 and 25 millimeters (one-half to 1 inch), and giant aneurysms measure more than 25 millimeters (larger than 1 inch).

Other risk factors associated with whether or not a cerebral aneurysm will rupture include:

There are a number of reasons cerebral aneurysms may develop, including:

• Genetic vulnerability (cerebral aneurysms may run in families)
• Head injury
• “Hardening of the arteries” (atherosclerosis)
• Complications from high blood pressure (hypertension)
• Disease or infection that affects the brain

Women are at slightly greater risk of developing cerebral aneurysms than men. Older people are also more vulnerable. Cerebral aneurysms can develop at any age. However, they are uncommon in children, accounting for fewer than two percent of all cases. Cerebral aneurysms in children are more often due to head injury and are more common in boys than in girls.

Cerebral aneurysms are classified into three types, based on their shape:

• Berry aneurysms, which is a type of saccular aneurysm that resembles a sac of blood attached to one side of the artery by a narrow neck. Most cerebral aneurysms are classified as berry, and they can occur in any artery in the brain. Multiple berry aneurysms can also develop.
  
  
• Dissecting aneurysms (or lateral aneurysms), in which the aneurysm bulges out on one side of the artery with a broad base (no narrow neck). Dissecting aneurysms are also considered a type of saccular aneurysm.
  
  
• Fusiform aneurysms, in which the aneurysm bulges out on both sides of the artery.

Along with other factors, the type of aneurysm determines the method of treatment.

Most unruptured aneurysms do not have symptoms. If symptoms are present, they will depend on the size of the aneurysm and its rate of growth. A larger aneurysm that is steadily growing may produce symptoms such as loss of feeling in the face or vision/eye problems.

When an aneurysm is about to rupture, some patients may experience a mild to moderate headache (sentinel headache). This symptom results from leaking of blood occurring just prior to the rupture of the aneurysm. However, it is often difficult to tell the difference between the occasional nagging headache that is harmless and the headache that may occur a day or two before an aneurysm ruptures.

When a cerebral aneurysm ruptures, patients typically experience a sudden and usually severe, blinding headache, sometimes called a "thunderclap" headache. Patients may also vomit, have a stiff neck, faint (a syncopal attack), or be very sensitive to bright light (photophobia).

Some people may go into a seizure or coma. Upon arriving at the hospital, people who are conscious and aware typically complain of an extremely severe headache and stiff neck. Some people arrive conscious but very groggy or confused. People who are alert generally have a better prognosis.

Researchers have also found that heart complications frequently accompany aneurysm rupture. Abnormal heart rhythms, including atrial fibrillation and atrial flutter, may occur, and in up to 20 percent of patients, there is damage to the heart muscle of the left ventricle and cardiac dysfunction. To measure the extent of cardiac damage, physicians will measure cardiac biomarkers including CK-MB and troponin I. Elevations in these markers signal damage to the heart muscle.

Studies have shown that patients with elevated cardiac biomarkers have a generally worse outcome than patients with normal cardiac biomarkers. The exact cause of cardiac damage in the event of a cerebral aneurysm rupture is unknown. Researchers suspect the underlying cause is multifactorial, or due to several different influences. These factors include the release of chemicals that restrict blood flow to the heart in response to the injury to the brain and alterations in the autonomic nervous system, which controls the heart rate.

Currently, angiography is the best way to detect an unruptured aneurysm. To perform an angiogram, a thin, hollow tube (catheter) is inserted through the femoral artery in the groin (or in the wrist) and all the way up to the brain. Once the catheter is in place, the physician injects a contrast dye that is visible under x-ray. These images help the physician locate the size and type of the aneurysm.

Noninvasive strategies are also available to detect unruptured aneurysms. These strategies include the standard magnetic resonance imaging (MRI) and a variant of the MRI called the magnetic resonance angiogram (MRA).

If an aneurysm has burst, a CAT scan of the head is the test most commonly used to detect the extent of the resulting bleeding in the brain. A CAT scan uses computerized technology to produce cross sectional-images of the body. In some patients, contrast medium (dye) may be used to produce highlighted, more detailed images of the brain.

To determine whether blood has traveled through the cerebrospinal fluid (CSF) around the brain and into the spinal cord, a CSF sample may be taken through a spinal tap for analysis. Finally, an electroencephalogram (EEG) may be ordered to help determine the cause of any seizures.

Treatment for a subarachnoid hemorrhage requires emergency medical assistance and ideally takes place in an intensive care unit. Once patients are admitted to the hospital, physicians will first attempt to correctly diagnose the event, stabilize the patient and locate the hemorrhage. During this time, preventing rebleeding and cerebral infarction (death of brain tissue due to lack of oxygen) are primary considerations, along with preventing vasospasm of the arteries. Vasospasm typically occurs no earlier than day three after the original event, and it is a major source of death and disability. In this early stage of treatment, a number of drugs might be used to prevent vasospasm, normalize blood pressure and reduce the risk of blood clots forming in the brain.

Whenever it is feasible, the patient will undergo surgery. The timing of surgery depends on complicated factors, including the risk of rebleeding and vasospasm versus the presence of swelling in the brain in the days immediately after the surgery. In some cases, surgery may be delayed by 14 days. In other cases, early surgery is warranted.

The approach toward an unruptured aneurysm is dictated by the risk of eventual rupture, with an eye toward reducing the risk. Surgery is generally considered the treatment of choice for an unruptured cerebral aneurysm, but when to do surgery, and for whom, remain controversial. The many factors under consideration include the patient’s age, general health and history of any previous ruptures, as well as characteristics of the aneurysm itself, including its size, location and whether it is growing, bleeding or putting pressure on the brain.

The most common surgical approach to a cerebral aneurysm is to use a small clip to cut off the blood supply to the aneurysm. The blood vessel that feeds the aneurysm is located and the clip is placed at the base of aneurysm. Clipping has been shown to be very effective depending on the type, location and size of the aneurysm. Overall, patients who have their aneurysms completely clipped do not experience a recurrence of the aneurysm. In some patients, the entire artery may be clamped off (occluded) and a blood vessel graft is used to reroute the blood flow around the damaged area.

Before surgery, the patient’s head will be shaved over the area of the aneurysm, and he or she will be given a sleep-inducing medication (general anesthesia). Then the surgeon will carefully cut open a small section of the skull, exposing the aneurysm. The surgeon will repair the aneurysm with the most appropriate procedure for the patient's condition.

An alternative to surgery is embolization. During this procedure, a thin, hollow tube catheter is inserted through an artery (usually in the groin or wrist) up to the site of the aneurysm. Once the catheter reaches the aneurysm, tiny balloons or coils inserted into the aneurysm. These devices block the blood from circulating in the aneurysm, causing the blood to clot. When the blood clots, it essentially destroys the aneurysm. Patients may need to undergo emobolization more than once in their lifetime.

If balloons are used, the procedure is also called balloon embolization. If the coils are used, the procedure is also called microcoil thrombosis. Though this technique is not used as often as clipping, it is less invasive and may offer an option for some aneurysm patients who are not candidates for surgery.

Because some cerebral aneurysms develop as a result of heart defects or other conditions that cannot be prevented, there are no specific prevention strategies for cerebral aneurysms. People who want to reduce their risk of suffering a ruptured cerebral aneurysm are encouraged to control their blood pressure, avoid or quit smoking and avoid heavy alcohol use. Physicians may also provide recommendations regarding medications (e.g. taking aspirin, discontinuing oral contraceptives).

Researchers continue to study various factors that can help determine which unruptured aneurysms should be surgically repaired. The findings of one large study suggested that aneurysms less than 7 millimeters (slightly smaller than a half an inch) have a low probability of rupture. Scientists examined vascular defects that also may contribute to the risk of rupture.

Researchers are currently working on additional strategies to treat and detect aneurysms. These strategies include a new drug, called proliNO, which may help treat cerebral vasospasms after an aneurysm rupture. They are also studying antibodies to molecules that promote vasospasm.

Additional research for the treatment of cerebral aneurysms includes:

• Less invasive, high resolution x-rays that can help physicians use stents (mesh-like tubes) to widen the artery and restore blood flow.
  
  
• Balloon angioplasty following a ruptured aneurysm to destroy the clot and control blood flow in the artery.
  
  
• Hypothermia during surgery to reduce the risk of postoperative complications and neurological damage.
  
  
• New coils for embolization treatment as well as improved techniques for replacing the coils.
  
  
• New methods for evaluating tissue for response to devices used in surgical repair of an aneurysm.
  
  
• Computer simulation model that assesses the outcomes of various surgical techniques in patients with cerebral aneurysms.

To evaluate risk factors for cerebral aneurysms, several groups of researchers are studying genetics, family medical histories and ethnic backgrounds for patterns of inheritance. They are examining the use of blood and tissue sampling for genetic linkage and molecular analysis. Other studies are focusing on prevention and treatment strategies for individuals who are at high risk for developing aneurysms based on genetic factors.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to cerebral aneurysm:

1. What tests will you use to determine if I have an aneurysm?
   
   
2. What type of aneurysm do I have and how big is it?
   
   
3. Where is the aneurysm located?
   
   
4. What are the chances that my aneurysm will rupture?
   
   
5. Do you recommend surgery and if so, what type?
   
   
6. How quickly do I need to have this surgery?
   
   
7. What are my risks with this type of surgery?
   
   
8. Will I likely need this surgery more than once?
   
   
9. If I do not have surgery, can anything increase the risk of rupture?
   
   
10. Should I make any lifestyle changes to reduce the risk of rupture?
    
    
11. Is there a chance my aneurysm can get bigger without treatment?
    
    
12. Do you recommend any medications or changes in my current medications?
    
    
13. How will you monitor the status of my aneurysm?
    
    
14. What signs or symptoms indicate that my aneurysm may be getting worse?
    
    
15. What signs indicate a medical emergency?
    
    
16. Does the aneurysm place me at risk for other vascular conditions?
    
    
17. Is it possible that I have more than one aneurysm?
    
    
18. Are my children at higher risk for developing an aneurysm?