A brain aneurysm is a bulge in an artery in the brain. The most common type resembles a round berry that is attached to the artery by a tiny stem. Most of these aneurysms develop because of congenital defects in artery walls. Between two and five percent of the population in the United States - as many as 15 million persons - have them. Risk factors include a family history of aneurysms, high blood pressure, and smoking.
The vast majority of small aneurysms pose little risk to health - if you have one, you probably won't know it because they rarely cause symptoms. The danger of any aneurysm, but especially larger ones, is rupture, creating a life-threatening emergency. Treatment usually is not recommended for small aneurysms but may be advised for large ones that are causing symptoms such as pain behind and above an eye, vision changes, numbness or weakness on one side of the face.
Relatively few aneurysm rupture each year - only about 30,000 of the millions estimated to exist.
If you know you have an aneurysm, to reduce risk don't smoke or use stimulant drugs (both of which can increase blood pressure), limit your caffeine intake (caffeine is a stimulant), avoid straining (this also can cause a spike in blood pressure), and talk to your physician about whether or not to avoid aspirin and other drugs, dietary supplements, and herbs that have blood-thinning effects.
While flying, with its reduced air pressure, could theoretically raise the risk of an aneurysm bursting, I can tell you that brain aneurysm is not listed among the contraindications to flying in the guidelines issued by the Aerospace Medical Association. And, given that an estimated 15 million people in the U.S. have brain aneurysms and that one billion people worldwide travel by air annually, I think it is safe to assume that many individuals with diagnosed or undiagnosed brain aneurysms fly safely every year. However, if you know you have one, check with your physician or a neurologist about your individual case.
Andrew Weil, M.D.