What are unruptured intracranial aneurysms?

  Unruptured intracranial aneurysms are balloon-like swellings of the blood vessels in the brain, found in about 3% of people. Most don’t cause symptoms or rupture, but in rare cases (about 1%), they can bleed. The ROAR study is analysing data from over 20,000 patients to better predict rupture risk and guide treatment.

A subarachnoid haemorrhage (SAH) is a type of stroke caused by bleeding into the space around the brain, often due to a ruptured aneurysm. It is a medical emergency that can lead to serious complications or death. The ROAR study aims to improve early identification of people at risk, helping to prevent these life-threatening bleeds through better prediction and treatment strategies.

Treatment decisions depend on the aneurysm’s size, location, and the patient’s overall risk. Larger aneurysms or those in high-risk areas are more likely to rupture. Risk factors like high blood pressure, smoking, or previous bleed from another aneurysm also increase rupture risk. While most unruptured aneurysms cause no symptoms, they can occasionally—but rarely—press on nearby nerves and cause problems such as double vision or drooping eyelids. Doctors carefully weigh the risk of rupture against treatment risks, with some cases best managed through regular monitoring.

Doctors use the PHASES score to estimate an individual’s risk of aneurysm rupture. This tool combines key factors—Population, Hypertension, Age, Size of aneurysm, Earlier SAH, and Site—to guide treatment decisions. A higher score suggests a greater risk of rupture and may support intervention, while a lower score may favour monitoring. The ROAR study is validating and improving this model to support more personalised decisions.

If treatment is needed, options include surgical clipping, where a metal clip is placed across the aneurysm to stop blood flow, or endovascular treatment, which involves inserting coils or a flow-diverting stent through the blood vessel to prevent rupture. While both approaches are effective, they are not without risk and potential complications including bleeding, stroke, or damage to surrounding brain tissue. The decision to treat is carefully balanced against the individual’s risk of rupture and overall health.

Currently, risk prediction models for unruptured intracranial aneurysms are limited in their scope. These models, unfortunately, rely on a small number of variables to estimate rupture risk. As a result, we are left with many aneurysms where the exact risk of rupture remains unclear. This limitation means that while some aneurysms are accurately assessed, others—potentially high-risk aneurysms—may be overlooked. The challenge lies in identifying which aneurysms will go on to rupture and which will remain stable.

Being diagnosed with an unruptured brain aneurysm can have a significant emotional and psychological impact on patients. Although most aneurysms never rupture, the uncertainty can cause ongoing anxiety and fear. Many patients worry about the risk of rupture during everyday activities, leading to changes in lifestyle, work, or social behaviour. Some may feel overwhelmed by the need to make complex decisions about monitoring or treatment—especially when the risk is unclear. Improved risk prediction models and clearer guidance can help reduce this burden by supporting more confident, personalised decisions.