Estimating Rupture Risk of Intracranial Aneurysms: What We Know, What We Do Not Know, and What We Need

Area of Science:

• Neurology
• Neurosurgery
• Epidemiology

Background:

• Management of unruptured intracranial aneurysms involves balancing rupture risk against procedural risks.
• Existing estimates of aneurysm rupture risk are derived from landmark natural history studies with substantial discrepancies, creating clinical uncertainty.

Purpose of the Study:

• To critically appraise existing natural history studies of unruptured intracranial aneurysms.
• To identify areas of agreement and contradiction among studies to guide future research directions.

Main Methods:

• Review and appraisal of landmark natural history studies on unruptured intracranial aneurysms.
• Analysis of reported rupture risk estimates, treatment rates, and influencing factors.
• Examination of methodological challenges including selection bias, crossover, incomplete follow-up, and regional variations.

Main Results:

• Short-term rupture risk is low but increases with aneurysm size, with annual estimates varying from 0.20% to 1.85%.
• Significant geographic variations in rupture risk and treatment rates were observed, with an inverse relationship between them.
• Methodological limitations, short follow-up periods, and extrapolation challenges hinder accurate lifetime risk assessment.

Conclusions:

• Discrepancies in rupture risk estimates stem from inherent methodological challenges and potential confounding factors like geography and treatment rates.
• Current data limitations necessitate larger, multicenter studies with longer follow-up and detailed phenotyping for more reliable clinical decision-making regarding unruptured intracranial aneurysms.