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. An aneurysm may be present from birth (congenital) or it may develop later in life. (For example, after a blood vessel is injured.)

There are many different types of aneurysms. A berry aneurysm can vary in size from a few millimeters to over a centimeter. Giant berry aneurysms can reach well over 2 centimeters. These are more common in adults. Multiple berry aneurysms are inherited more often than other types of aneurysms.

Other types of cerebral aneurysm involve widening of an entire blood vessel, or they may appear as a "ballooning out" of part of a blood vessel. Such 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.

About 5% of the population has some type of aneurysm in the brain. Risk factors include a family history of cerebral aneurysms, and certain medical problems such as 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. Symptoms occur if the aneurysm pushes on nearby structures in the brain.

Symptoms depend on what structure the aneurysm pushes on, but may include:

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

A sudden, severe headache (often described as "the worst headache of your life") is one symptom that an aneurysm has ruptured. Other symptoms of an aneurysm rupture may include:

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

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 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
• CSF exam (spinal tap)
• MRI of the head (CT scans may be better at showing bleeding in the brain)
• Cerebral angiography or spiral CT scan angiography of the head to reveal the location and size of the aneurysm
• Electroencephalogram (EEG) if seizures occur

Symptoms often do not appear until bleeding (a rupture) occurs. A ruptured cerebral aneurysm is an emergency condition. The goal of treatment is to control symptoms and prevent further bleeding. Lowering blood pressure can reduce the risk.

Neurosurgery is the main treatment for cerebral aneurysm. The base of the aneurysm is closed off with clamps, sutures, or other materials that prevent blood flow through the aneurysm.

In many cases, an alternative to surgery can be done by placing special coils or stents into the aneurysm through the arteries, which causes a clot to form and prevents further bleeding. This approach is considered less invasive than brain surgery, and in the appropriate circumstances, it is regarded as the best form of treatment.

If surgery cannot be done because of the patient's overall condition or the aneurym's location or size, medical treatment is similar to treatment for subarachnoid hemorrhage. Treatment may involve:

• Complete bedrest and activity restrictions
• Drugs to prevent seizures
• Medicines to control headaches and blood pressure

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.

• Increased fluid pressure inside the skull
• Loss of movement in one or more parts of the body
• Other neurological problems (such as vision changes, difficulty speaking, or cognitive decline)
• Permanent loss of sensation of any part of the face or body
• Seizures, epilepsy
• Stroke
• Subarachnoid hemorrhage

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, especially if it is severe or “the worst headache ever.”

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.