A brain aneurysm is a bulge in a blood vessel in your brain. It can be very serious if it bursts.
Symptoms of a brain aneurysm can include headaches or changes in your vision. If it bursts, it can cause a sudden and very severe headache.
Brain aneurysms are usually treated with surgery if they have burst or there's a risk they will burst.
It's not clear what causes brain aneurysms. You're more likely to get them if you smoke, have high blood pressure or have family members with them.