A brain aneurysm is an abnormal, outward pouching of the artery wall due to a weakness in the wall at that particular site. I frequently use the analogy of a broken garden hose. The wall of an aneurysm is very, very thin and this is why it ruptures. All 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, but frequently a baby is born with a weakness in the arterial wall. A few medical syndromes, such as Polycystic Kidney Disease are associated with brain aneurysms, and these patients require screening.
The most significant risk factors for brain aneurysm are cigarette smoking and having a close relative who has an aneurysm. Most aneurysms are incidental, meaning that if you have one; it is unlikely that anyone else in your family has one. However, a small percentage of aneurysms run in families, and if you have two or more close relatives with a history of brain aneurysm, it is strongly recommended that all next-of-kin be screened.
Brain aneurysms affect more females than males (3:2), and 15-20% of patients have multiple (two or more) aneurysms. The average age at presentation is usually between 40-60 years of age, but I’ve treated small children, teenagers, and adults into their 80’s.
Aneurysms are classified by their size and shape:
By Shape:
- A berry shape is the most common. It is a small saccular shaped aneurysm resembling a berry.
- The fusiform shape is an elongated, spindle-shaped dilation.
- The dissecting aneurysm splits an artery wall through a small tear.
By Size:
- Small – less than 10 mm (most commonly aneurysms are 4-7 mm in size)
- Large – 10-25 mm (a dime is 18 mm)
- Giant – Greater than 25 mm
Approximately 85% of aneurysms develop in the anterior (front) portion/circulation of the brain; 15% are found in the posterior (back) portion/circulation of the brain.
The most common locations are: Anterior Communicating (A-com) aneurysm, Posterior Communicating (P-com) aneurysm, Middle Cerebral Artery (MCA) aneurysm, Carotid Bifurcation aneurysm, Basilar tip aneurysm, and PICA aneurysm.
The risk of an aneurysm rupture is estimated at 1% per year and may vary 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. A higher incidence of aneurysm rupture occurs during Spring and Fall; however, the reason for this has not been fully explained.
Patients with ruptured aneurysm often complain of a severe headache, and describe it as “the worst headache of my life!” A subarachnoid bleed (hemorrhage) is considered a medical emergency with potential major complications to the patient. Up to 30% of these patients die before arriving at the hospital. Another 30% are at major risk for stroke, since bleeding from the aneurysm will often cause the major blood vessels of the brain to become severly narrowed. This condition is called vasospasm. Many patients after surviving aneurysm rupture and vasospasm are permanently disabled and are unable to return to their previous activities.
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 of CT & CTA (computed tomography and CT angiogram), and MRI & MRA (magnetic resonance imaging and MR angiogram). These advanced diagnostic tools are now used commonly to assess patients with these complaints; although many patients with aneurysms will need a cerebral angiogram for definitive diagnosis and to determine the best course of treatment.
