• Ajay Malhotra, Xiao Wu, Howard P Forman, Holly K Grossetta Nardini, Charles C Matouk, Dheeraj Gandhi, Christopher Moore, and Pina Sanelli.
• From Yale School of Medicine and Yale University, New Haven, Connecticut; University of Maryland School of Medicine, Baltimore, Maryland; and Northwell Health, Manhasset, New York.
• Ann. Intern. Med. 2017 Jul 4; 167 (1): 26-33.

BackgroundSmall unruptured intracranial aneurysms (UIAs) are increasingly diagnosed. Management depends on growth and rupture risks, which may vary by aneurysm size.PurposeTo 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 SourcesMEDLINE, EMBASE, Scopus, and the Cochrane Library from inception to 2017 (with no language restrictions).Study SelectionPublished case series and observational studies that reported natural history data on UIAs 7 mm and smaller.Data Extraction2 reviewers abstracted study information, evaluated study quality, and graded strength of evidence.Data SynthesisOf 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.LimitationHeterogeneous definitions of growth; heterogeneous and selective treatment and follow-up methods, particularly in high-risk patients.ConclusionPoor-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 SourceNone.

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