Patients with a condition that causes blood vessels in the brain to form an abnormal tangle could be helped by new research.
An international patient trial suggests that the safest way of managing arteriovenous malformations (AVM) of the brain is to treat the patient's symptoms only, and not the AVM.
People with an AVM - causing disrupted blood flow in the brain - are three times more likely to suffer stroke from the AVM bursting or die within three years if the tangled vessels are treated, researchers found.
An AVM occurs when blood passes directly from arteries to veins - normally arteries carry blood from the heart to the brain, while veins take blood back in the opposite direction
"We have found clear evidence of harm to patients in the short term from treatments to obliterate AVMs that have never bled in the past, " says Professor Rustam Al-Shahi Salman, of the University of Edinburgh's Division of Clinical Neurosciences.
"Observation of trial participants must continue for at least another five years to find out if this difference persists," he adds.
More than 200 patients with a brain AVM were followed for 33 months in a trial, which was led in the UK by the University of Edinburgh.
The risks linked to treatment of AVMs were much higher than those associated with leaving them alone, the trial found.
The findings build on previous research showing that annually, only one in every hundred patients with a brain AVM suffer a stroke, and the other 99 per cent do not.
Doctors say that if a brain AVM ruptures, the initial effects are often mild.
Common symptoms of the condition include headaches and epilepsy.