Introduction

 The Risk of Aneurysm Rupture (ROAR) study is the largest research project of its kind in the world and aims to transform how we assess the risk of brain aneurysms rupturing.

Unruptured brain aneurysms – bulges in blood vessels in the brain – are surprisingly common, affecting around 3% of the population. While many never cause harm, some can rupture (about 1% per year) and lead to a rare type of stroke called subarachnoid haemorrhage, which is fatal in about 30% of cases.

To prevent this, doctors can treat aneurysms before they rupture. However, these treatments – whether surgical or endovasular – carry significant risks, with complication rates between 5% and 8%. That’s why it’s crucial to identify which aneurysms are truly at high risk of rupturing, so treatment is given only when it’s likely to do more good than harm. Currently, tools like the PHASES score are used to estimate a patient’s 5-year rupture risk, but these tools have limitations and have never been validated in the UK.

The ROAR study is tackling this challenge by following up over 20,00 patients with unruptured brain aneurysms, using national databases of hospital admissions and deaths. So far, ROAR includes more than 100,000 years of patient follow-up — 30 times more than any previous study — and this will double by the end of the project.

The goal of this study is to test how accuracy of the PHASES score and to develop a better, more reliable prediction model to guide treatment decisions. This will help ensure that patients get the right care at the right time, potentially saving lives and avoiding unnecessary procedures.

To deepen our understanding even further, we’re expanding the ROAR programme through a series of linked projects:

• ROAR-DNA will explore the genetic factors that might influence aneurysm formation and rupture.
• ROAR-FLOW will investigate how the shape of aneurysms and the way blood flows through them can affect rupture risk.
• ROAR-GP will link hospital data with general practice (GP) records to give a more complete picture of patients’ health over time.

Together, these studies will provide a comprehensive, long-term view of brain aneurysm risk and help deliver safer, more personalised care to thousands of patients in the UK and beyond.