Brain (Cerebral) Aneurysms

What is Cerebral (Brain) Aneurysm?

An aneurysm is an abnormal, outward swelling of an artery caused by weakness in the arterial wall. Brain aneurysms may be associated with other medical conditions including hypertension, vessel wall defects, flow dynamics, smoking, atherosclerosis, and defective vessel repair mechanisms. Aneurysms are more prevalent among women (60%), and 20% of patients have two or more aneurysms. The average age of aneurysm patients is between 40 and 60 years. They are rare in childhood. Most cerebral aneurysms (85%) occur in the front (anterior) part of the brain. The other 15% are found in the back (posterior) part of the brain.

Epidemiology studies suggest that as many as 5% of people in the United States harbor a cerebral aneurysm by age 75. About 30,000 people per year suffer an aneurysmal subarachnoid hemorrhage (SAH). The yearly risk of rupture from an asymptomatic unruptured aneurysm is about 1-2% each year depending on the size and location of the lesion as well as other factors.

Onset is usually sudden and without warning. Rupture of a cerebral aneurysm is dangerous and results in bleeding in the brain or in the area surrounding the brain, leading to an intracranial hematoma (a mass of blood -- usually clotted -- within the skull). There are also delayed problems of water on the brain (hydrocephalus), and narrowing of the blood vessels because of the irritation of the blood on the blood vessels known as vasospasm. Rebleeding, hydrocephalus, and vasospasm can happen days to weeks after the initial bleed.

How do they develop?

It is not clear why a person develops a cerebral aneurysm. They are very uncommon in patients below 20 years of age and are increasingly common in older patients. It appears they are related to an absence of a muscular layer that makes up part of the blood vessels that over time stretches and thins and creates the aneurysm. Smoking appears to markedly increase the chance that one will develop a cerebral aneurysm.

Aneurysms develop at branching points in the main arteries at the base of the skull. This suggests that they develop at the area in the blood vessel experiencing the greatest force of the blood stream.

What are the dangers?

As stated above, the primary danger of cerebral aneurysms is the risk of rupture, producing subarachnoid hemorrhage. Once this occurs, about 1/3 of patients die before reaching a hospital. Another 1/3 or are disabled as a result of the initial hemorrhage, and 7% die from the later development of vasospasm (to be discussed below), regardless of treatment. Hospitalized patients have an average 40% mortality rate over the first several days after hemorrhage up to 1 month. Overall mortality at the end of one month has been found to be as high as 60%. No more than one-third of patients eventually return to a functional life. This fact is especially tragic considering the relatively young average age of these patients,; about 50 years old.

In addition to the first hemorrhage, rebleeding is a major cause of death and disability. The highest risk of rebleeding is within the first 1 to 7 days and may result in death for 20% of the initial survivors.

For those who survive the initial period following rupture, whether or not rebleeding has occurred, the threat of vasospasm is high. This is a process of narrowing of the arteries carrying blood to the brain. When this narrowing reaches a significant degree, blood flow is compromised and the brain may suffer damage, either reversible or irreversible. This state of inadequate oxygen delivery is called ischemic (stroke). Vasospasm is probably caused by breakdown products from the blood. It usually begins on the 3rd day after hemorrhage, peaks at about 7 days, and often resolves by 12 days. During the peak period about half of patients will develop some degree of vasospasm. The symptoms depend on the severity of the spasm and its location, that is, what areas of the brain have diminished blood supply. As mentioned, vasospasm claims an additional 7% of deaths, but the rate of permanent disability is much higher. It has been estimated that if 5 people suffer a bleed today, in one year, only one person will be alive and well a year later. One person will be disabled and three will be dead.

How is an aneurysm diagnosed?

If an aneurysm bleeds, the patient almost always has a severe headache that prompts the patient to seek medical attention. A CT scan of the brain or a Lumbar puncture usually identifies the blood outside the blood vessel and is called a subarachnoid hemorrhage (SAH). An angiogram is usually performed to identify the exact blood vessel that has bled and the detailed anatomy of the aneurysm.

Why should it be treated?

Treatment of the aneurysms recommended to

1. minimize rebleeding
2. treat the hydrocephalus
3. treat the vasospasm.