Identifying the warning signs of a brain aneurysm can be challenging—even for experienced medical professionals. These silent health threats can develop without any warning signs until they leak or rupture. Because they can be so sneaky, knowing what to look for isn’t just important—it’s literally lifesaving.
The Mayo Clinic defines a brain aneurysm as “a bulge or ballooning in a blood vessel in the brain. It often looks like a berry hanging on a stem.” Some remain small and never become a problem, but others become so large that they become a ticking time bomb.
The actual danger comes in the form of a rupture, which leads to a hemorrhagic stroke—bleeding in the brain. Most often, the rupture occurs in the space between the brain and the tissues that cover it (a subarachnoid hemorrhage). These hemorrhages are extremely dangerous and carry a high potential for causing permanent neurological damage or even death.
The difficulty in detecting an aneurysm before it ruptures is that, in many instances, there is no “preview.” However, when the body does signal that something is wrong, these signs tend to be unmistakable. Here are 12 signs you should never ignore.
The 12 Warning Signs of a Brain Aneurysm
According to the Mayo Clinic, the following signs may indicate that an aneurysm is present, leaking, or about to rupture:
1. Sudden and Severe Headache (The “Thunderclap” Headache)
What it feels like: Often described as “the worst headache of my life,” this headache strikes suddenly and with overwhelming intensity. It’s not a typical tension headache or migraine—it’s a blinding, explosive pain that comes out of nowhere.
According to the Brain Aneurysm Foundation, a headache is always the first symptom that a person with a leaking or bursting aneurysm will experience. But it isn’t a run-of-the-mill headache that goes away in a few minutes or after taking a pill. This kind of headache is:
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Sudden and extremely severe
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Persistent—it just won’t go away on its own
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Often accompanied by nausea, vomiting, or vision changes
When an aneurysm starts leaking a small amount of blood, it’s called a sentinel bleed. This may produce a severe headache that lasts for a few days—a literal “shot across the bow” warning that a full rupture could be just around the corner.
What to do: Never try to “tough out” a headache like this. If you or someone you’re with experiences a sudden, blinding headache, call for emergency help immediately. And whatever you do—don’t drive yourself to the hospital—a rupture could cause you to pass out behind the wheel in seconds.
2. Blurred or Double Vision
What it looks like: Vision may become hazy, unfocused, or you may see two images of a single object. This occurs because the aneurysm can press on nerves that control eye movement and visual processing.
Why it happens: The oculomotor nerve, which controls most of your eye movements and pupil function, runs close to common aneurysm locations. Pressure on this nerve can disrupt normal vision.
3. Confusion or Disorientation
What it feels like: Suddenly feeling “out of it,” struggling to understand where you are, or having difficulty following conversations. You may feel like your thoughts are scrambled or slow.
Why it happens: Bleeding in the brain can impair cognitive function, affecting your ability to process information, make decisions, or orient yourself to your surroundings.
4. One Dilated Pupil
What it looks like: One pupil appears noticeably larger than the other, and it may not respond normally to light changes.
Why it happens: Pressure from the aneurysm can compress the oculomotor nerve on one side, causing the pupil on that side to dilate. This is a particularly concerning neurological sign that warrants immediate attention.
5. One Drooping Eyelid
What it looks like: The upper eyelid on one side appears to sag or droop, sometimes covering part of the eye.
Why it happens: Same mechanism as the dilated pupil—pressure on the oculomotor nerve on one side can cause eyelid weakness or drooping (ptosis).
