Growth, rupture risk appear low for small intracranial aneurysms, review indicates

The annualized rupture rate was 0% for aneurysms 3 mm or smaller, below 0.5% for aneurysms 5 mm or smaller, and below 1% for aneurysms 7 mm or smaller.


Small unruptured intracranial aneurysms have low rates of growth and rupture, according to a new study.

Researchers performed a systematic review of studies that reported natural history data on unruptured intracranial aneurysms 7 mm or smaller. The goal of the study was to summarize evidence about growth and rupture risk of such aneurysms and determine whether these variables differed for very small and small aneurysms, defined as 3 mm or smaller and 5 mm or smaller, respectively. The study results were published online June 6 by Annals of Internal Medicine.

Twenty-six cases series and observational studies were included in the review. Of these, five described the growth rate of aneurysms 3 mm or smaller, 10 described the growth rate of aneurysms 5 mm or smaller, and eight described the growth rate of aneurysms 7 mm or smaller. Rupture rates by size, meanwhile, were reported in seven, 11, and 13 studies, respectively. Nineteen studies used data from patients at a single center, and seven used multicenter patient data. For all three aneurysm sizes, the annualized growth rate was below 3% in all but one of the studies, while the annualized rupture rate was 0% for aneurysms 3 mm or smaller, below 0.5% for aneurysms 5 mm or smaller, and below 1% for aneurysms 7 mm or smaller.

The strength of evidence for both outcomes was of poor quality, the authors noted. In addition, the included studies used different definitions of growth as well as different treatment and follow-up methods. However, despite these limitations, the authors concluded that small unruptured intracranial aneurysms have low rates of both growth and rupture, especially those that are 3 mm in diameter or smaller, although they stressed that better evidence is needed and that standardized definitions of growth should be used. The American Heart Association/American Stroke Association 2015 guidelines, which recommend a first follow-up study six to 12 months after initial discovery and follow-up yearly or every other year, may need to be revised to specifically consider small aneurysms, the study authors concluded.

An accompanying editorial complimented the study authors on their detailed review but agreed that their research was limited by the poor quality of the available data. “One should not conclude from this study that small aneurysms have no risk for rupture but rather that experts are skilled at predicting which aneurysms are more likely to rupture,” the editorialist wrote. “Thus, all patients with aneurysms should be evaluated by an expert who can review associated risk factors and determine both the optimal follow-up plan (if any) and the need for treatment.”