Three million to six million people in the United States have brain aneurysms but do not know it, according to the Brain Aneurysm Foundation in Boston. Aneurysms form when artery walls weaken, but the underlying cause is unknown. Most do not rupture.
But 30,000 people a year do suffer ruptures, with dreadful results. Half die within a month, and many survivors wind up with significant brain damage.
