The condition involves a kind of tangle in the brain called an arteriovenous malformation, or AVM. Arteries and veins grow knotted together until eventually some of them burst, causing a bleeding stroke. AVM accounts for a small fraction of hemorrhagic strokes.
But increasingly, brain scans can spot these tangles well before they're at risk of bleeding raising the question of what to do for patients, if anything. The study aimed to tell if treating them could prevent a stroke later in life.
Early results suggest it may be safer to leave the condition alone, said Columbia University neurologist Dr. Jay Mohr, who helped lead the study.
Nearly three years into the research, the rate of strokes and death was more than three times higher among participants who had received surgery, radiation or other invasive treatment than among patients given medication for headaches and other symptoms.
Mohr couldn't provide precise numbers but said most of the cases were strokes and there were very few deaths.
"From what we can see, our current methods of intervention may pose a greater hazard for health than letting the natural history run itself out," Mohr said.
The National Institutes of Health has stopped enrollment in the study, but participants will be tracked for several more years to see how they fare over time.