Authored by MCN Neurologists
An aneurysm is a bulge that develops in an artery due to a weakness in the wall of the artery. The walls of arteries in the brain are made up of three layers. If the outermost layer of the arterial wall becomes weak, the inner layers can poke through into a balloon-like shape.
The exact reasons why some people develop aneurysms in the brain are not known. It is believed that genetics play a role because aneurysms are more common in those with first-degree relatives with aneurysms. Overall, between 2-5% of the population have brain aneurysms. They are somewhat more common in females. Not all aneurysms rupture.
Symptoms of a Brain Aneurysm
A brain aneurysm may be clinically silent, that is, it produces no symptoms, and may be discovered on a brain scan performed for some other reason. If an aneurysm becomes sufficiently large, it may press upon neighboring areas of the brain and produce symptoms, such as a droopy eyelid or double vision. The most common symptom of a brain aneurysm is headache. Keep in mind, however, that headaches are very common in the general population and most headaches are not due to brain aneurysms. Sometimes the aneurysm may start to leak blood and can produce frequent, severe headaches – these have been called “warning leaks” or “sentinel bleeds.” A change in the character of headaches – more frequent or more intense than usual – should be cause for concern.
The real danger of a brain aneurysm is that it can burst, releasing a large amount of blood around the brain. This is a very serious medical condition called subarachnoid hemorrhage. The most common symptom of subarachnoid hemorrhage is a sudden severe headache, often described by sufferers as “the worst headache of my life.” Depending upon the extent of bleeding, there may be a variety of other symptoms that can progress to unconsciousness, coma and even death.
Diagnosis of a Brain Aneurysm
Because a burst brain aneurysm has such severe consequences, it is important to discover aneurysms before they burst (unruptured aneurysms). A variety of modern imaging techniques have made the diagnosis of brain aneurysms much simpler and more accurate than in the past. It can be challenging, however, to decide when to perform such testing. In general, an onset of unexplained headaches or a change in the pattern of established headaches are considered good reasons for further testing. A variation of CT or MRI scanning, called CT-angiography (CTA) and MR-angiography (MRA) respectively, can produce images of the blood vessels surrounding the brain. These tests can show aneurysms, provided they are big enough to detect. In some cases, catheter angiography may be required either to diagnose or better define an aneurysm that is discovered by CTA or MRA. In this test, a very thin, flexible tube called a catheter, is introduced into an artery in the groin and threaded up into the arteries of the brain. Dye is injected and x-rays are taken to produce images of the blood vessels.
If a patient presents with a sudden, severe headache due to subarachnoid hemorrhage (due to a ruptured aneurysm), in most cases, a plain CT scan of the head will show the bleeding. Rarely, the doctor may have to perform a spinal tap, in which a needle is introduced into the spinal canal in the back to remove some of the fluid that surrounds the brain. Normally, this fluid is clear, like water. In subarachnoid hemorrhage due to a burst aneurysm or warning leak, the fluid is bloody or tinged with blood.
Treatment of a Brain Aneurysm
As mentioned earlier, the greatest risk of a brain aneurysm is that it can burst, often with catastrophic consequences. Therefore, when an unruptured aneurysm is discovered, the primary focus of treatment is to reduce the chance of the aneurysm bursting. In general, there are two factors that determine the risk of rupture – the size of the aneurysm and its location. The larger the aneurysm, the greater the risk of rupture. Aneurysms smaller than 5 mm have a low risk of rupture. Similarly, aneurysms that are located on certain blood vessels in the brain carry higher risks of bleeding. Other risk factors that increase the likelihood of an aneurysm rupturing are smoking and high blood pressure.
Once a brain aneurysm is discovered, the patient should seek consultation either with a neurosurgeon, an interventional neuro-radiologist or a neurologist who specializes in stroke to discuss the pros and cons of various treatments.
Traditionally, surgery has been performed to treat brain aneurysms. The neurosurgeon opens the skull, exposes the aneurysm and places a clip (like a clothes pin) across the “neck” of the aneurysm collapsing the balloon-like sac of the aneurysm and preventing it from bursting in the future. However, many aneurysms are located deep in the crevices of the brain and cannot be approached easily without risking damage to normal brain tissue during surgery. There may also be other reasons why surgery cannot be performed with an acceptable level of risk.
More recently, a newer technique of treating brain aneurysms without surgery has been developed. A catheter is introduced into an artery in the groin, and threaded up through the blood vessels of the brain into the aneurysm. A special soft platinum wire is passed through the catheter into the aneurysm. It is then coiled until it fills the aneurysm, is detached, and left behind in the aneurysm sac. Over time, due to the presence of the coiled wire, the blood within the aneurysm sac solidifies and thus fills the sac. This process is called “coiling.”
Whether to perform surgery or coiling is a complex decision that depends upon many factors including the aneurysm’s size and shape, the presence or absence of a defined “neck,” the location of the aneurysm in the brain and the patient’s age and general medical condition.
Monitoring Brain Aneurysms
If a small aneurysm is discovered incidentally a decision may be made to hold off on treatment. The aneurysm, however, will need to be monitored periodically because aneurysms can grow in size, increasing the risk of rupturing. Monitoring may involve performing CT or MR angiography every year, or more or less frequently, depending upon the circumstances.
Screening for Brain Aneurysms
First-degree relatives (parents, children and siblings) of patients with aneurysms are often advised to undergo CT or MR angiography as a screening test to determine whether they might have aneurysms.