Most brain aneurysms cause no symptoms at all. About 3% of adults are living with an unruptured aneurysm right now and have no idea, because small aneurysms rarely press on anything or produce warning signs. That means “knowing” you have one usually comes down to two scenarios: recognizing the subtle symptoms of a large unruptured aneurysm, or experiencing the unmistakable emergency of a rupture.
Most Aneurysms Are Completely Silent
A brain aneurysm is a bulge in a weakened section of an artery wall. When the bulge is small, it sits quietly inside your skull without affecting nearby tissue. There’s no headache, no dizziness, no sign anything is wrong. This is why aneurysms are so often discovered by accident, when someone gets a brain scan for an unrelated reason like a head injury or chronic migraines.
The 5-year risk of rupture for these incidentally discovered aneurysms is roughly 1.3%, so the vast majority of people who have one will never experience a medical emergency from it. Still, certain aneurysms carry higher risk depending on their size, shape, and location inside the brain.
Symptoms of a Large Unruptured Aneurysm
When an aneurysm grows large enough, it can press on surrounding brain tissue or nerves. This is the closest thing to a “warning sign” that an aneurysm exists before it ruptures. Symptoms typically affect one side of your head or face and include:
- Pain above and behind one eye, often persistent and localized
- A dilated pupil in one eye, sometimes noticeably larger than the other
- Double vision or other vision changes
- Numbness or tingling on one side of your face
- Seizures
These symptoms develop because the swollen artery is physically compressing a cranial nerve. The combination of one-sided eye pain with a visibly enlarged pupil is particularly suggestive. If you’re experiencing this pattern, it warrants urgent medical evaluation, not because rupture is imminent, but because the aneurysm is large enough to cause neurological damage on its own.
The Sentinel Headache: A Possible Early Warning
Between 15% and 60% of people who eventually suffer a full aneurysm rupture report having an unusually severe, sudden headache in the days or weeks beforehand. This is sometimes called a sentinel headache, and it may result from a tiny leak of blood from the aneurysm before it fully breaks open.
What makes it distinctive is the combination of sudden onset and unusual severity. It’s not a headache that builds gradually over hours. It arrives abruptly, lasts more than an hour, and feels different from any headache you’ve had before. The problem is that this kind of headache is easy to dismiss or attribute to stress, and it often doesn’t lead to a diagnosis before the larger rupture occurs. If you experience a sudden, explosive headache unlike anything you’ve felt previously, treat it seriously.
What a Rupture Feels Like
A ruptured brain aneurysm produces what’s often described as the worst headache of your life. It hits suddenly, reaching maximum intensity within seconds. People frequently describe it as feeling like being struck in the head. This is a medical emergency that requires calling emergency services immediately.
Along with the headache, a rupture commonly causes a stiff neck, nausea and vomiting, sensitivity to light, blurred or double vision, confusion, loss of consciousness, and sometimes seizures. Not everyone experiences all of these, but the thunderclap headache, one that peaks almost instantly, is the hallmark symptom. Roughly half of people who suffer a rupture do not survive, which is why speed matters enormously.
Who Should Get Screened
Since most aneurysms don’t produce symptoms, the only reliable way to find one early is through imaging. But routine screening isn’t recommended for everyone. It’s generally reserved for people whose risk is meaningfully elevated.
Mayo Clinic recommends regular brain MRI for people with a family history of aneurysm. If you have a first-degree relative (parent or sibling) who had a brain aneurysm or a ruptured aneurysm, screening is reasonable. Certain genetic conditions also raise your risk. Polycystic kidney disease and connective tissue disorders are the most common ones associated with aneurysm formation.
Beyond genetics, the two most significant modifiable risk factors are smoking and high blood pressure. A large genetic study published in the Journal of the American Heart Association found that smoking roughly tripled the odds of developing a brain aneurysm. High blood pressure showed a similarly strong effect: for every 10 mm Hg increase in diastolic blood pressure (the bottom number), the risk of aneurysm nearly tripled as well. If you smoke and have uncontrolled blood pressure, your combined risk is substantially elevated.
How Aneurysms Are Found and Diagnosed
When doctors suspect an aneurysm or want to screen for one, they typically start with noninvasive imaging. An MRA (magnetic resonance angiography) uses magnetic fields to create detailed pictures of blood vessels in the brain without radiation. A CTA (CT angiography) uses X-rays with a contrast dye injected through a vein and produces high-resolution images quickly, making it the go-to option in emergency situations.
The gold standard for confirming an aneurysm and planning treatment is a digital subtraction angiography, which involves threading a thin catheter through an artery (usually starting at the groin) up to the brain’s blood vessels. This provides the most detailed view but is more invasive and carries a small risk of complications, so it’s typically reserved for cases where the noninvasive scans are inconclusive or when treatment planning requires precise detail. CTA is excellent at confirming an aneurysm is present but can miss very small ones, particularly in certain locations near the base of the brain.
What Happens After an Aneurysm Is Found
Finding an unruptured aneurysm doesn’t automatically mean surgery. The decision depends on several factors: the aneurysm’s size, its location, its shape, and your age and overall health. Aneurysms larger than 7 mm are generally considered higher risk, based on two of the largest international studies on the topic. But that threshold isn’t universal. Some locations in the brain are more dangerous than others. A 4 mm aneurysm in the front-connecting artery of the brain, for example, carries more risk than a same-sized one in a different location, because the average size of ruptured aneurysms in that area is only about 5.5 mm.
Irregular shape also matters. An aneurysm with an uneven, bumpy surface is more concerning than a smooth, round one of the same size. For small, regularly shaped aneurysms in lower-risk locations, doctors often recommend monitoring with repeat imaging every 6 to 12 months rather than immediate intervention.
When treatment is recommended, the two main approaches both aim to stop blood from flowing into the aneurysm. One involves placing a small metal clip at the base of the aneurysm through an opening in the skull. The other threads a catheter through your blood vessels and fills the aneurysm with tiny coils or redirects blood flow with a stent-like device. The catheter-based approach is less invasive and generally has a shorter recovery, but the best option depends on the specific aneurysm.
Reducing Your Risk
You can’t change your family history or genetics, but the two biggest controllable risk factors are well within reach. Quitting smoking and managing blood pressure are the most impactful things you can do if you’re concerned about brain aneurysms. Given that both smoking and elevated blood pressure roughly triple the risk independently, addressing even one of them makes a meaningful difference. Regular blood pressure checks, staying physically active, and limiting excessive alcohol intake all contribute to keeping artery walls healthier and under less strain.