I am very sorry to hear about your sister. And it’s understandable that you’d be worried.

A brain aneurysm is a balloon-like pouch that sticks out from the wall of an artery inside the brain. If it bursts, blood pours into the brain, and that can be fatal. But most such aneurysms never burst.

About 10–15 million people in the United States have them. About 30,000 rupture each year. The risk increases with age and the size of the aneurysm. Where in the brain the aneurysm is located is another factor.

Brain aneurysms do run in families. They’re also associated with several diseases, including polycystic kidney disease and Ehlers-Danlos and Marfan’s syndromes.

Noninvasive imaging tests like magnetic resonance angiography (MRA) and CT angiography (CTA) can find them with reasonable accuracy. The problem is that predicting whether an aneurysm is likely to rupture is difficult. Also the available treatments to prevent rupture — some of which involve surgery and other procedures within the artery — are risky.

So, even if there is a small aneurysm, is the risk of treatment greater than the risk of rupture? Often it’s hard to say.

In general, though, experts recommend that people be screened for brain aneurysms if two or more first-degree relatives (parent, sibling, or child) have them. You have only one first-degree relative who is known to have an aneurysm. So strictly speaking you don’t need screening.