Brain Aneurysms
An aneurysm is an abnormal, outward swelling (bubbling) of the wall of the artery due to a weakness in the wall at that particular site. Those aneurysms involving the arteries in the brain are a serious medical condition. They can either rupture (bleed) resulting in death or stroke or they can compress surrounding brain tissue or cranial nerves, which can result in progressive neurological deficits.
Brain aneurysms are usually acquired with age. The most significant risk factors are cigarette smoking and having a close relative who had an aneurysm. They affect more females over males (3:2), and 20% of patients have multiple (two or more) aneurysms. The average age at presentation is usually 40-60 years old. Aneurysms are classified by their size and shape:
By Shape:
- The berry shape is the most common type. It is a small saccular shaped aneurysm that resembles a berry.
- The fusiform shape is an elongated, spindle-shaped dilation.
- The dissecting aneurysm is a splitting of an artery wall through a small tear.
By Size:
- Small <10mm
- Large 10-25mm (a dime is 18mm)
- Giant <25mm
Approximately 85% of aneurysms develop in the anterior (front) part/circulation of the brain whereas 15% are found in the posterior (back) part/circulation of the brain.
The risk of an aneurysm rupture is estimated at 1% to 2% per year and varies with aneurysm type, size, location, and history of previous aneurysm rupture. When a brain aneurysm does rupture, the blood usually goes into the subarachnoid space (a space that closely surrounds the brain), or less commonly directly into the brain substance. These patients often complain of a severe headache and describe it as "the worst headache of my life!" A subarachnoid bleed is considered a medical emergency with potential major complications to the patient. Up to 25% of those patients will die before getting to the hospital. Another 25% are at major risk for stroke since the bleeding from the aneurysm will often cause the major blood vessels of the brain to become severely narrowed. This is a condition called vasospasm.
Most patients have no symptoms or complaints until the aneurysm ruptures. In 40% of cases, there are some warning signs that an aneurysm is present such as pain above and behind the eye, nerve paralysis, localized headache, neck pain, nausea and vomiting. Fortunately, an increasing number of aneurysms are found prior to rupturing because CT (computed tomography) and MRI (magnetic resonance imaging) are now used commonly to assess patients with these complaints. Although CT and MR can show many aneurysms, most patients with aneurysms need a cerebral angiogram for definitive diagnosis and to determine the best course of treatment.