Growth and Rupture Risk of Small Unruptured Intracranial Aneurysms: A Systematic Review.

Background: Small unruptured intracranial aneurysms (UIAs) are increasingly diagnosed. Management depends on growth and rupture risks, which may vary by aneurysm size.

Purpose: To summarize evidence about the growth and rupture risk of UIAs 7 mm and smaller and to explore differences in growth and rupture risks of very small (≤3 mm) and small (≤5 mm) aneurysms.

Data Sources: MEDLINE, EMBASE, Scopus, and the Cochrane Library from inception to 2017 (with no language restrictions).

Study Selection: Published case series and observational studies that reported natural history data on UIAs 7 mm and smaller.

Data Extraction: 2 reviewers abstracted study information, evaluated study quality, and graded strength of evidence.

Data Synthesis: Of 26 studies, 5, 10, and 8 described the growth rate of aneurysms 3 mm and smaller, 5 mm and smaller, and 7 mm and smaller, respectively, whereas rupture rates were reported in 7, 11, and 13 studies for aneurysms 3 mm and smaller, 5 mm and smaller, and 7 mm and smaller, respectively. The annualized growth rate was less than 3% in all but 1 study for all 3 size categories. The annualized rupture rate was 0%, less than 0.5%, and less than 1% for the 3 size categories, respectively. Strength of evidence was very low quality for growth rates and low quality for rupture rates.

Limitation: Heterogeneous definitions of growth; heterogeneous and selective treatment and follow-up methods, particularly in high-risk patients.

Conclusion: Poor-quality evidence suggests that small UIAs have low growth and rupture rates and very small UIAs have little or no risk for rupture.

Primary Funding Source: None.