Most brain aneurysms do not cause headaches. Between 80% and 90% of unruptured aneurysms are discovered incidentally during brain imaging done for other reasons, and the majority produce no symptoms at all. However, aneurysms can cause head pain in specific circumstances, and the type of headache matters enormously. A sudden, explosive headache is a medical emergency, while chronic or recurring headaches are rarely linked to an unruptured aneurysm.
Why Most Aneurysms Are Silent
A brain aneurysm is a balloon-like bulge in an artery wall. Most are small, and small aneurysms typically sit quietly without pressing on anything. They don’t stretch pain-sensing structures, don’t irritate surrounding tissue, and don’t leak blood. People can live their entire lives without knowing one is there.
When someone with chronic headaches or migraines gets a brain scan and an aneurysm shows up, it’s natural to assume the aneurysm is the cause. In most cases, it isn’t. Chronic headaches and migraines are rarely related to an unruptured aneurysm. The two are usually a coincidence: headaches are extremely common, and aneurysms affect roughly 3% of the population, so overlap is inevitable.
When an Unruptured Aneurysm Does Cause Pain
Larger unruptured aneurysms can press on brain tissue or nerves, and this compression is one way an intact aneurysm produces symptoms. The pain tends to be localized, often behind or around one eye, and it may come with neurological signs that point to nerve involvement.
An aneurysm pressing on the nerve that controls eye movement can cause a distinctive combination of symptoms: a drooping eyelid, a dilated pupil that doesn’t react normally to light, and an eye that drifts outward and downward. Double vision can occur, though the drooping eyelid often blocks it. Aneurysms arising from certain arteries near the base of the brain are the most common culprits for this kind of nerve compression. A new headache paired with any of these eye-related changes is a red flag that needs urgent evaluation.
The Thunderclap Headache of a Rupture
When an aneurysm ruptures, it leaks blood into the space surrounding the brain. This triggers a thunderclap headache: a very severe headache that reaches its maximum intensity within one minute or less. The defining feature is not just how bad it hurts but how fast it arrives. People often describe it as the worst headache of their life, with the pain peaking almost instantly rather than building gradually.
A thunderclap headache can occur on its own or alongside other symptoms like neck stiffness, nausea, sensitivity to light, confusion, seizures, or weakness on one side of the body. In a study of over 2,100 patients with acute-onset headaches, roughly 6% of those with confirmed bleeding from an aneurysm had headaches that took up to an hour to peak rather than hitting within one minute. So while rapid onset is the hallmark, not every case fits the textbook perfectly.
Sentinel Headaches: A Warning Before Rupture
A sentinel headache is a sudden, severe headache that occurs days to weeks before a major aneurysm rupture. It’s thought to result from a tiny leak or changes in the aneurysm wall as it becomes unstable. Estimates of how often this happens vary widely: studies report that 15% to 60% of people who eventually have a full rupture experienced a sentinel headache beforehand. One study found that 62% of patients reported headaches in the year before their aneurysm ruptured, compared to 33% of healthy volunteers.
Sentinel headaches are sudden and severe but often lack a clear location. They typically appear within four weeks before a major bleed. The challenge is that they’re difficult to distinguish from ordinary bad headaches in the moment, and they’re frequently dismissed by both patients and doctors. Research has also suggested that not just a new headache but a change in a person’s usual headache pattern could signal that an aneurysm is becoming unstable.
Despite growing recognition of sentinel headaches, they are not yet formally included among the standard warning factors that guide treatment decisions for known unruptured aneurysms. Some researchers argue this should change, pointing to evidence that when a headache does signal impending rupture, treatment ideally needs to happen within a week of symptom onset.
Headaches That Warrant Immediate Attention
The vast majority of headaches have nothing to do with aneurysms. But certain patterns should prompt urgent medical evaluation:
- Sudden onset at full intensity: a headache that goes from zero to severe within seconds to one minute, unlike anything you’ve experienced before.
- New headache with eye changes: pain around one eye combined with a drooping eyelid, dilated pupil, or double vision.
- Worst headache of your life: particularly if it began abruptly rather than building over hours.
- Headache with neurological symptoms: confusion, neck stiffness, seizures, vision loss, or weakness on one side of the body.
- A sudden change in your usual headache pattern: especially if you have a known aneurysm, a headache that feels fundamentally different from your baseline deserves attention.
What This Means If You Have a Known Aneurysm
If you’ve been told you have a small, unruptured aneurysm and you also get headaches, the two are probably unrelated. Most small aneurysms are monitored over time with periodic imaging rather than treated immediately, and having one doesn’t mean every headache is dangerous.
What does matter is recognizing something new. A headache that is sudden, unusually severe, and unlike your typical pattern is worth reporting promptly, especially if it comes with visual changes or neurological symptoms. The question of whether a new headache around a known aneurysm should trigger earlier treatment is still debated among specialists, but erring on the side of getting evaluated quickly is reasonable when the stakes are this high.