An aneurysm is an abnormal widening or ballooning of a section of a blood vessel. When an aneurysm occurs in the brain, it is called a cerebral aneurysm.

Aneurysms in the brain occur when there is a weakened area in the wall of a blood vessel. They may occur as a congenital (present from before birth) defect or may develop later in life. It is estimated that 5% of the population has some type of aneurysm in the brain.

A saccular aneurysm (berry aneurysm) can vary in size from a few millimeters to over a centimeter. Giant berry aneurysms can reach well over 2 centimeters. The aneurysm resembles a sack of blood attached to one side of the blood vessel by a narrow neck. These are more common in adults. Multiple berry aneurysms are not unusual.

Other types of cerebral aneurysm may involve widening (dilatation) of the entire circumference of the blood vessel in an area, or may appear as a ballooning out of part of a blood vessel. These types of aneurysms can occur in any blood vessel that supplies the brain. Trauma and infection, which can injure the blood vessel wall, can cause such aneurysms.

Risk factors include a family history of cerebral aneurysms, and some medical problems, including polycystic kidney disease and coarctation of the aorta.

Aneurysms usually cause no symptoms unless they rupture and cause bleeding into the brain. Often, an aneurysm is found when a CT scan or MRI is performed for another reason. If the aneurysm gets big enough to push on nearby structures, it can cause the following symptoms:

• Double vision
• Loss of vision
• Headaches
• Eye pain
• Neck pain

Symptoms of an aneurysm that have broken open (ruptured) may include:

• Sudden occurrence of a severe headache (often described as "the worst headache of your life")
• Headaches with nausea or vomiting
• Stiff neck (occasionally)
• Muscle weakness, difficulty moving any part of the body
• Numbness or decreased sensation in any part of the body
• Vision changes (double vision, loss of vision)
• Eyelid drooping
• Confusion, lethargic, sleepiness, or stupor
• Seizures
• Slow, sluggish, lethargic movement
• Speech impairment
• Sudden onset of irritability, impulsivity, or poor temper control

NOTE: A ruptured aneurysm is a medical emergency. Seek immediate medical help.

An eye exam may show increased pressure within the brain (raised intracranial pressure), including swelling of the optic nerve (papilledema) or bleeding into the retina of the eye.

The following tests may be used to diagnose cerebral aneurysm and determine the cause of bleeding within the brain:

• CT scan of the head can identify bleeding and occasionally locate the aneurysm.
• CSF (cerebrospinal fluid) examination (spinal tap) may confirm bleeding.
• MRI of the head may be an alternative to a CT scan, but is not as good at showing bleeding in the brain.
• Cerebral angiography or spiral CT scan angiography of the head is used to pinpoint the location and size of the aneurysm.
• EEG (electroencephalogram) may be performed if seizures occur.

Because symptoms often do not appear until bleeding occurs, a ruptured cerebral aneurysm is an emergency condition when it is discovered. The goal of treatment is to control symptoms and prevent further bleeding. Lowering blood pressure can reduce the risk of further bleeding.

Neurosurgery is the primary treatment for cerebral aneurysm. The base of the aneurysm is closed off with clamps, sutures, or other methods that prevent blood flow through the aneurysm. In many cases, special coils or stents can be placed into the aneurysm through the arteries.

This causes a clot to form in the aneurysm and prevents further bleeding. This is considered a less invasive approach than brain surgery, and in the appropriate circumstances, it is regarded as the best form of treatment.

If surgery is not feasible because of the location or size of the aneurysm or the condition of the person, medical treatment is similar to treatment for subarachnoid hemorrhage.

This may include restricting activity (often complete bedrest is advised), treating symptoms such as headache, controlling blood pressure, and prescribing preventive use of antiseizure medications.

Once the aneurysm is repaired, prevention of stroke due to blood vessel spasm may be necessary. This may include intravenous fluids, certain medications, and actually letting one's blood pressure run high.

The outcome varies. Patients who are in deep comas after an aneurysm rupture generally do not do as well as those with less severe symptoms.

Ruptured cerebral aneurysms are often deadly. About 25% of people die within 1 day, and another 25% die within about 3 months. Of those who survive, more than half will have some sort of permanent disability.

• Subarachnoid hemorrhage
• Stroke
• Seizures, epilepsy
• Paralysis of any part of the body
• Permanent loss of sensation of any part of the face or body
• Other neurologic deficits (such as vision changes, loss of speech ability, cognitive decline)
• Communicating hydrocephalus

Go to the emergency room or call the local emergency number (such as 911) if sudden or severe headache occurs, particularly if you also have nausea, vomiting, seizures, or any other neurological symptoms. Also call if you have a headache that is unusual for you.

There is no known way to prevent the formation of a cerebral aneurysm. If discovered in time, unruptured aneurysms can be treated before causing problems.

The decision to repair an unruptured cerebral aneurysm is based on the size and location of the aneurysm, and the patient's age and general health. It must be carefully considered given the risks both in operating and in watchful waiting.