What is a brain aneurysm and what causes a brain aneurysm?

The brain gets its blood supply from arteries known as the Circle of Willis. It is located at the base of the brain and is a loop of arteries that join in a circle then send branches out to all parts of the brain. These arteries deliver nutrition (glucose and oxygen) to the brain cells.

The junctions where these arteries come together can form weak spots. These weak spots can balloon out and fill with blood, creating the outpouchings of blood vessels known as aneurysms. These sac-like areas may leak or rupture spilling blood into surrounding tissues. While the prevailing thought has been that aneurysms are congenital (meaning that people are born with them), it is now thought that they are due to microscopic damage to the artery walls caused by abnormal flow at the junction points where the arteries come together.

There are other rare causes of aneurysms. Mycotic aneurysms are cause by infections of the artery wall. Tumors and trauma can also cause aneurysms to form. Drug abuse, especially cocaine, can cause the artery walls to inflame and weaken.

Brain aneurysms (aneurysms within arteries in the brain) are a common occurrence. At autopsy, incidental asymptomatic aneurysms are found in more than 1% of people. Most aneurysms remain small and never become an issue or are diagnosed. Some, however, may gradually get larger and exert pressure on surrounding brain tissue and nerves and may be diagnosed because of facial symptoms such as:

• headache,
• numbness, or weakness of one side of the face,
• a dilated pupil, or
• change in vision.

The greater concern is a brain aneurysm that leaks or ruptures, and potentially causes stroke or death. Bleeding leaks into one of the membranes that covers the brain and spinal canal and is known as a subarachnoid hemorrhage (sub= beneath + arachnoid=one of the brain coverings + hemorrhage=bleeding).

What are the symptoms of brain aneurysm?

The headache associated with a leaking aneurysm is severe. Blood is very irritating to the brain and causes significant pain. Patients may describe the "worst headache of their life," and the healthcare provider needs to have an appreciation of brain aneurysm as a potential cause of this type of pain. The headache may be associated with nausea, vomiting, and change in vision. A subarachnoid hemorrhage also causes pain and stiffness of the neck.

How is brain aneurysm diagnosed?

The diagnosis of brain aneurysm begins with a high index of suspicion by the healthcare provider. The history of the headache, an acute onset of the worst headache of the patient's life, associated with a stiff neck and an ill-appearing patient on physical examination, typically lead the healthcare provider to order a CT (computerized tomography) scan of the head. This will show a subarachnoid hemorrhage in more than 90% of cases of ruptured aneurysm. In the few cases that are not recognized by CT, the healthcare provider may consider performing a lumbar puncture (LP, or spinal tap) to identify blood in the cerebrospinal fluid that runs in the subarachnoid space.

If the CT or the LP reveals the presence of blood, angiography is performed to identify where the aneurysm is located and to plan treatment. Angiography (angio=artery +graphy= picture) is a procedure in which a small flexible tube is threaded into one of the brain's arteries, and dye is injected while pictures are taken. Newer technology allows angiography to be done in association with CT or magnetic resonance imaging (MRI).

Though the symptoms may suggest a brain aneurysm, other diagnoses may need to be considered. Migraine headache, meningitis, tumor, and stroke all may cause neurologic symptoms. Based on the patient's presentation, the healthcare provider will need to decide which tests and studies to use to establish the correct diagnosis.

What is the treatment for brain aneurysm?

Treatment for a symptomatic aneurysm is to repair the blood vessels. Clipping and coiling are two treatment options.

• Clipping: A neurosurgeon can operate on the brain by cutting open the skull, identifying the damaged blood vessel and putting a clip across the aneurysm. This prevents blood from entering the aneurysm and causing further growth or blood leakage.
  
  
• Coiling: An interventional radiologist can thread a tube through the arteries, as with an angiogram, identify the aneurysm, and fill it with coils of platinum wire or with latex. This prevents further blood from entering the aneurysm.

Both these options have the risk of damaging the blood vessel and causing more bleeding, damaging nearby brain tissue, and causing the surrounding blood vessels to go into spasm; depriving brain tissue of blood supply and causing a stroke.

Prior, during, and after surgery, attention is paid to protect the brain and its blood vessels from potential further damage. Vitals signs are monitored frequently, and heart monitors are used to watch for abnormal heart rhythms. Medications may be used to prevent blood vessel spasm, seizure, agitation, and pain.

What is the outcome of brain aneurysm?

Brain aneurysms are deadly. About 10% of patients with a ruptured aneurysm die before receiving medical care. If untreated, another 50% will die within a month, with 25% of patients sustaining another bleeding episode within a week. Aside from the bleeding issues, there is significant risk of artery spasm leading to stroke.

Survival rates are increased by early presentation to the hospital, early aneurysm repair, and control of potential blood vessel spasm with medications.

What are future directions for the treatment of brain aneurysm?

For those who survive an initial aneurysm rupture, blood vessel spasm (vasospasm) may be the villain in causing continued brain damage. Experiments to develop new drugs to control vasospasm are ongoing. Molecules that can cause spasm are being identified, and antibodies may be able to be produced to blunt their effect.

Studies are also looking at the possibility that brain aneurysms may be hereditary, and perhaps screening of high-risk populations may be possible in the future.

sourceLast Editorial Review: 1/9/2008

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