What is a brain aneurysm?
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 brain or cerebral aneurysm.
What are the causes?
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 due to weakened by disease, injury or an anomaly present at birth. Most of the times aneurysms occur without any apparent cause. Aneurysms are often associated and may be made worse by high blood pressure. They are potentially life-threatening, and serious consequences - such as a stroke - can result if one bursts in the brain. This is called a haemorrhagic (or bleeding) stroke. When a blood vessel on the brain's surface ruptures and bleeds into the space between the brain and an overlying fine spidery web like membrane called arachnoid, it is called a subarachnoid haemorrhage. When an artery bursts within the brain, flooding the surrounding tissue with blood, it is a cerebral haemorrhage.
The factors that contribute to the formation of brain aneurysms:
- Traumatic head injury
- Use of alcohol
- Use of oral contraceptives
- Family history of brain aneurysms
- Other inherited disorders: Polycystic kidney disease
What are the types?
A saccular aneurysm (berry aneurysm) can vary in size from a few millimeters to over a centimetre. Giant berry aneurysms can reach well over 2 cm. 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.
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 which supplies the brain. Trauma and infection, which can injure the blood vessel wall, can cause such aneurysms.
What are the symptoms?
Aneurysms usually cause no symptoms unless they rupture and cause bleeding into the brain. Often, an aneurysm is found when a CAT scan or MRI is performed for an unrelated reason. Occasionally, the aneurysm gets big enough to compress nearby structures and can cause symptoms such as:
- Double vision
- Loss of vision
- Eye and neck pain
Symptoms of an aneurysm that has bled may include:
- Sudden occurrence of a severe headache (described as ‘the worst in patient's experience’, ‘bolt from the blue’)
- 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
- Changes in mental status, the person may be confused, lethargic, sleepy
- Slow, sluggish, lethargic movement
- Speech impairment
- Sudden onset of irritability, impulsivity or poor temper control
How is it diagnosed?
There may be signs of increased pressure within the brain (raised intracranial pressure) including swelling of the optic nerve or tiny haemorrhages into the retina of the eye, which are evident on careful eye examination.
A brain aneurysm is usually diagnosed by tests to determine the cause of bleeding within the brain:
- A CT scan of the head can identify bleeding and occasionally locate the aneurysm
- A CSF (cerebrospinal fluid) examination (spinal tap) may confirm bleeding when CT scan is non-diagnostic
- An MRI of the head may be an alternative to a CT scan, but is not as sensitive to bleeding within the brain (subarachnoid bleeding). Various MRI scans vary in their ability to detect smaller aneurysms
- Cerebral angiography is considered the gold standard in evaluating the location and size of the aneurysms.
- CT angiography or angiography with the latest generation of CT scans are as sensitive and give more anatomic information than cerebral angiography.
- EEG (electroencephalogram) may be performed if seizures occur
What is the treatment?
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/brain aneurysm. The base of the aneurysm is closed off with camps, sutures, or other methods that prevent blood flow through the aneurysm. In many cases, special coils 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 haemorrhage. 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 due to irritation by degrading blood products on arteries may be necessary. This may include intravenous fluids, certain medications, and actually letting one's blood pressure run high.
What is the prognosis?
The outcome varies. The best indicator for prognosis is the patient's status after the aneurysm ruptures. Patients who are deeply comatose after an aneurysm rupture generally do not do as well as those with minimal symptoms.
A cerebral aneurysm that does not rupture may not cause any symptoms. If one is discovered which has not ruptured, treatment must be considered carefully. The risks related to brain surgery are high and attempting to prevent the aneurysm from rupturing by operating on it may actually cause rupture and all the potential problems that can result.
However, about 25% of ruptured cerebral aneurysms are fatal within 24 hours. Approximately another 25% are fatal within about 3 months. Of the remaining people with ruptured cerebral aneurysm, more than one-half will have some sort of permanent disability.
What is the prevention?
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, the age of the patient, and general state of medical health.