A brain aneurysm is a bulge or ballooning that develops in a weakened area of a blood vessel within or around the brain. Many individuals can have a brain aneurysm without being aware of it, as they often remain “silent” and cause no noticeable symptoms until they rupture. This asymptomatic nature means that a significant number of these aneurysms go undetected for extended periods.
The Nature of Unruptured Aneurysms
Unruptured brain aneurysms frequently do not produce symptoms, especially when they are small. They often do not press on nearby nerves or brain tissue, which is why they remain asymptomatic. Many unruptured aneurysms are discovered incidentally during imaging tests, such as MRI or CT scans, performed for other medical conditions. Estimates suggest up to 1 in 20 people may have an unruptured aneurysm. Not all unruptured aneurysms will burst. The risk of rupture is generally low, estimated to be around 0.6% to 1.3% annually for asymptomatic aneurysms. Larger aneurysms, typically those over 7 mm, carry a higher risk of rupture compared to smaller ones. Aneurysms located in the posterior circulation of the brain may also have a greater tendency to rupture.
Recognizing a Ruptured Aneurysm
When a brain aneurysm ruptures, it causes a sudden and severe event, often described as the “worst headache of life” or a “thunderclap headache.” A ruptured aneurysm causes blood to spill into the surrounding brain tissue, which is a life-threatening medical emergency known as a subarachnoid hemorrhage. Along with the excruciating headache, a ruptured aneurysm can present with several other symptoms. These may include nausea and vomiting, a stiff neck, blurred or double vision, and increased sensitivity to light. Some individuals might also experience seizures, a drooping eyelid, a dilated pupil, pain above and behind the eye, confusion, weakness, numbness, or even loss of consciousness. Immediate medical attention is necessary if these symptoms occur.
How Aneurysms Are Discovered
Brain aneurysms are identified through various diagnostic imaging techniques. When a ruptured aneurysm is suspected, a computed tomography (CT) scan is often the initial test to detect bleeding. A CT angiogram (CTA) provides more detailed images of the brain’s blood vessels and can help pinpoint the aneurysm’s size, location, and shape. CTA is quick and accessible, making it valuable in emergency situations. Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) are also used to visualize aneurysms. MRA is a non-invasive test that uses magnetic fields and radio waves to create detailed images of brain arteries. For a more precise diagnosis, particularly when other tests are inconclusive, a cerebral angiogram may be performed. This invasive procedure involves inserting a catheter into a blood vessel, typically in the groin, and guiding it to the brain to inject a contrast dye, providing highly detailed X-ray images of the cerebral arteries.
Factors Increasing Risk
Several factors increase an individual’s risk of developing a brain aneurysm. Modifiable risk factors include high blood pressure, which puts strain on blood vessel walls, and smoking. Drug abuse, especially cocaine use, is also associated with an elevated risk. Non-modifiable factors also contribute to aneurysm risk. These include a family history of brain aneurysms, particularly if two or more first-degree relatives have been affected. Certain inherited genetic disorders, such as autosomal dominant polycystic kidney disease, Ehlers-Danlos syndrome, and Marfan syndrome, can weaken blood vessel walls and increase susceptibility. While these factors increase risk, many individuals with aneurysms do not have any of these known risk factors.
Managing a Discovered Aneurysm
Once a brain aneurysm is discovered, management decisions depend on several factors, including the aneurysm’s size, location, and the estimated risk of rupture. For small, unruptured aneurysms that are not causing symptoms, a “watchful waiting” approach may be recommended. This involves regular monitoring with imaging scans to check for any changes in the aneurysm’s size or characteristics. When intervention is necessary, such as for higher-risk or ruptured aneurysms, two main approaches are typically considered. Surgical clipping involves a neurosurgeon making an incision in the skull to access the aneurysm and placing a small metal clip at its base to stop blood flow into it. Endovascular coiling is a less invasive procedure where a catheter is threaded through a blood vessel to the aneurysm, and tiny platinum coils are deployed inside to block blood flow and promote clotting. Both methods aim to prevent blood from entering the aneurysm, thus reducing the risk of rupture or re-bleeding.