December 9, 1998
Web posted at: 8:51 p.m. EST (0151 GMT)

BOSTON (CNN) -- The best treatment for some brain aneurysms may be no treatment, according to a new study.

Aneurysms are weak spots on blood vessels that balloon out from the vessel wall. If they break, they can cause a stroke. About 5 percent of Americans have had a brain aneurysm or will develop one.

Researchers at the Mayo Clinic found that for a small aneurysm -- less than three-eighths of an inch wide -- the chance that it will break is less than one-twentieth of 1 percent a year. In contrast, the risk of death or brain damage from surgery to repair such an aneurysm is about 10 percent.

However, if the aneurysm is larger or if a patient has already had an aneurysm that ruptured, the chance that the blood vessel will burst increases substantially, making surgery possibly worth the risk, the researchers concluded.

Results of the study, which involved about 1,500 patients in the United States, Canada and Europe, are reported in Thursday's New England Journal of Medicine.

The question of preventive surgery for aneurysms is coming up more and more because brain scans performed for other reasons are detecting more aneurysms. In contrast, 10 years ago, doctors were finding only one non-ruptured aneurysm for every nine that had already burst.

While most brain aneurysms never rupture, the result if they do is death in more than half the cases.

"You don't like to be walking around knowing there's a weakness in a blood vessel in your brain and it can pop out and kill you. You want to think there's something you can do," said Dr. John Marler of the National Institutes of Health, which paid for the study. "This helps answer the question, 'What should I do now that you've found this thing?'"

Marler estimates that doctors operate on only about 1 percent of small aneurysms that aren't causing any other problems. Still, that amounts to about 100,000 operations a year, which the study's results indicate could be avoided.

Other doctors warned that the study should not be taken as a warning against any surgery, emphasizing that each case must be decided on its own merits.

"A generalization that an intracranial aneurysm is little risk and nothing needs to be done would be grossly misleading and dangerous," said Dr. Neil Martin, a neurosurgeon at the UCLA Stroke Center.

But surgery to remove an aneurysm carries its own set of dangers, including stroke, brain damage or death. The location of the aneurysm affects the risk, as does a patient's age.

The rate of death or disability from an operation goes from 6.5 percent for someone under 45 to 32 percent for patients 65 and older.

The Associated Press and Reuters contributed to this report.