An aneurysm is defined as a blood-filled sac in a blood vessel caused by dilation or weakening of the blood vessel wall. A cerebral aneurysm, also known as an intracerebral aneurysm or an intracranial aneurysm, is specifically defined as a dilated and weakened portion of a cerebral blood vessel that is prone to rupture. The thin walls of a cerebral aneurysm do not have the same structure as normal vascular walls and hence do not have as much strength as normal vascular walls. This allows a cerebral aneurysm to enlarge over time due to vascular pressure. The main risk associated with a cerebral aneurysm is that it may rupture and cause bleeding within the brain, known as subarachnoid hemorrhage (SAH). An artist's rendition of a cerebral aneurysm is shown below.

The following is a shaded surface display of a large cerebral aneurysm originating from the posterior cerebral artery. In this display, the cranial bones have been segmental away to allow for complete visualization of the aneurysm and the associated blood vessels.

Cerebral aneurysms are believed to develop due a focal weakening in the walls of a cerebral blood vessel. Most often this focal weakening occurs at a bifurcation, or branch point, in the blood vessel. A number of factors may contribute to the formation of cerebral aneurysms including:

• Genetic predisposition / family history
• Severe head trauma
• Brain tumor
• Atherosclerotic heart disease
• Long standing, poorly controlled hypertension
• Cigarette smoking
• Excess alcohol consumption

There are three main types of cerebral aneurysms.

• A saccular cerebral aneurysm is a small sac of blood which is attached to a cerebral blood vessel by a narrow neck. This type of aneurysm is also known as a berry aneurysm because the aneurysm on the blood vessel resembles a berry on branch. The most common type of cerebral aneurysm, a saccular aneurysm may occur in any part of the brain but is most common in the large arteries at the base of the brain; it is not uncommon for a patient to present with multiple saccular cerebral aneurysms. Saccular cerebral aneurysms are most common in adults and have been known to run in families. The artist's rendition of a cerebral aneurysm above depicts a saccular cerebral aneurysm.
• Another type of cerebral aneurysm is a ballooning of the blood vessel. This type of cerebral aneurysm may occur in any part of the brain. The shaded surface display above shows a ballooning cerebral aneurysm.
• The third main type of cerebral aneurysm is a widening of an entire blood vessel. Like the ballooning cerebral aneurysm, this type of cerebral aneurysm may occur in any part of the brain.

There is a separate category of cerebral aneurysms known as traumatic aneurysms (TAs) which result from traumatic brain injury (TBI) involving penetrating injuries or fractures of the skull base or anterior cranial fossa. TAs may develop and / or rupture more than a month after the initial TBI and are often fatal, especially when they rupture. TAs may be of any of the three types described above. However, TAs account for less than 1% of all cerebral aneurysms.

A cerebral aneurysm may occur in anyone at any age. However, cerebral aneurysms are more common in adults than in children and are slightly more common in women than in men. Autopsy studies have estimated that 1% - 5% of the population has a cerebral aneurysm of some variety and severity. However, only 5 out of every 100,000 patients present with a ruptured cerebral aneurysm annually. The average age of patients presenting with a ruptured cerebral aneurysm is approximately 50.

In most cases, an unruptured cerebral aneurysm will not cause any symptoms. However, in rare cases a patient with an unruptured cerebral aneurysm may experience sudden and unusually severe headaches, nausea, vomiting, vision impairment, and loss of consciousness.

The symptoms of a ruptured cerebral aneurysm include:

• Sudden, severe, "thunderclap" headaches which are described as "the worst in the patient's experience"
• Nausea
• Vomiting
• Stiff Neck
• Vision impairment
• Drooping eye lids
• Speech impairment
• Muscle weakness or difficulty moving any part of the body
• Numbness or decreased sensation in any part of the body
• Seizures
• Changes in mental status, i.e., the patient may become lethargic, sleepy, stuporous, irritable, or unable to control their temper
• Loss of nervy function (i.e. neurologic deficits) may occur in any part of the body if the ruptured aneurysm causes pressure on adjacent brain tissue or if there is reduced cerebral circulation due to a spasm of the blood vessels adjacent to the ruptured cerebral aneurysm

Once a patient has presented with a combination of conditions symptomatic of a ruptured cerebral aneurysm, a diagnosis is usually made based upon tests to determine the cause and location of bleeding within the brain.

• A CT scan of the head is able to indicate intracranial bleeding and occasionally may be able to locate the ruptured cerebral aneurysm. However, in some cases the amount of bleeding is too small to be detected by a CT scan.
• A CSF (cerebrospinal fluid) examination may be able to confirm the presence of intracranial bleeding when the CT scan is non-diagnostic due to an insufficient amount of bleeding.
• An MRI of the head may be used as an alternative to a CT scan but is not as sensitive to subarachnoid bleeding as a CT scan.
• Cerebral angiography is able to pinpoint the location of the ruptured cerebral aneurysm.
• An EED (electroencephalogram) may be performed if seizures occur.

See Page 2: Treatment of Cerebral Aneurysms for information on the treatment of cerebral aneurysms.

The prognosis for a patient with a ruptured cerebral aneurysm depends on a number of factors including:

• Time between the rupture of the cerebral aneurysm and diagnosis and treatment of the cerebral aneurysm
• Location of the ruptured cerebral aneurysm
• Extent of the ruptured cerebral aneurysm
• Patient's age
• Patient's general health

The breakdown of outcomes of ruptured cerebral aneurysms are as follows:

• 25% of patients - fatal within 24 hours
• 25% of patients - fatal within 3 months
• 25% of patients - recovery with some sort of permanent disability such as paralysis of any part of the body, permanent loss of sensation in any part of the body, or neurologic deficits such as vision changes and loss of speech ability
• 25% of patients - complete recovery

Currently there is no known way to prevent the formation of a cerebral aneurysm. However, if a cerebral aneurysm is discovered in time it may be treated so as to prevent rupture. See Page 2: Treatment of Cerebral Aneurysms for information on how to prevent the rupture of a cerebral aneurysm.

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