De novo aneurysm formation and growth of untreated aneurysms: a 5-year MRA follow-up in a large cohort of patients with coiled aneurysms and review of the literature.

Background And Purpose: Rates of development of de novo intracranial aneurysms and of growth of untreated additional aneurysms are largely unknown. We performed MRA in a large patient cohort with coiled aneurysms at 5-year follow-up.

Methods: In 276 patients with coiled intracranial aneurysms and 5±0.5 years of follow-up MRA (totaling 1332 follow-up patient-years), additional aneurysms were classified as unchanged, grown, de novo, or incomparable with previous imaging. We calculated 5-year cumulative incidence of de novo aneurysm formation and growth of untreated aneurysms. We searched PubMed and EMBASE databases for studies assessing aneurysm development, and growth.

Results: In 50 of 276 patients (18%), 75 additional aneurysms were present at follow-up MRA. Of these 75, 2 were de novo (both 3 mm), 58 were unchanged, 5 had grown from 1 to 3 mm (7.9% of 63 known additional aneurysms; 95% CI, 1.3%-14.6%), and 10 were incomparable. Five-year cumulative incidence for a de novo aneurysm developing was 0.75%. Four additional aneurysms in 3 patients were treated. Ten previous studies reported annual incidences of growth of additional aneurysms ranging from 1.51% to 22.7%, and 5 studies reported annual incidences of de novo aneurysm formation ranging from 0.3 to 1.8%.

Conclusions: MRA screening of patients with coiled aneurysms within the first 5 years after treatment has a low rate of de novo aneurysm development and growth of additional aneurysms, and an even lower treatment rate.