A new study has found that treating patients who suffer from a common condition that affects blood vessels in the brain increases their risk of stroke.
People with a condition known as arteriovenous malformation (AVM) - which causes blood vessels in the brain to tangle - have a better outcome if doctors treat their symptoms only and not the AVM.
A team of doctors looked at the long-term outcome of patients with the condition, which is caused by abnormal connections between the arteries and veins in the brain.
This is the first study to compare the risks and benefits of treatment for AVM in the long term. The findings build on previous research that reported an increased risk of stroke in the first three years after treatment for AVM.
AVM affects around 1 in 2000 people. Although most people with the condition can lead relatively normal lives, they live with the risk that the tangles can burst and bleed into the brain at any time, causing a stroke. Around one in every hundred AVM patients suffers a stroke each year.
In some cases doctors can surgically remove the tangle or block the blood vessels involved to reduce the risk of bleeding. However, treatment can sometimes increase the chances that the tangle will burst and bleed into the brain, resulting in a stroke.
Professor Rustam Al-Shahi Salman, MRC Senior Clinical Fellow at the University of Edinburgh and a consultant neurologist, said: "Many patients feel that living with AVM is like living with a time bomb in your head that could explode at any time. Patients and their doctors face difficult choices when deciding whether or not to pursue treatment. We have found that, for most people whose AVM has not caused a bleed, the risks of treatment exceed the risks of leaving it alone over 12 years."