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  • Natural History of Unruptured Intracranial Aneurysms: A Meta-Analysis of Prospective Studies

    Final Number:

    Robert F. Rudy BS; Hormuzdiyar H. Dasenbrock MD; Rose Du MD, PhD

    Study Design:

    Subject Category:
    Aneurysm/Subarachnoid Hemorrhage

    Meeting: AANS/CNS Cerebrovascular Section 2016 Annual Meeting

    Introduction: The predictors of the rupture of cerebral aneurysms remain only partially understood. Further assessment of the hemorrhage risk of cerebral aneurysms may aid cerebrovascular surgeons when comparing the risk of subarachnoid hemorrhage with the periprocedural risk from aneurysm obliteration. The goal of this study was to perform a study-level meta-analysis of prospective, longitudinal studies to estimate the annual subarachnoid hemorrhage rate and predictors of cerebral aneurysm rupture.

    Methods: The Medline, EMBASE, and Cochran databases were queried for studies evaluating the hemorrhage risk of unruptured intracranial aneurysms that were published through May 5th, 2015. Records identified in the search were screened by abstract and relevant articles were obtained and read in full to determine eligibility. Longitudinal, prospective studies with data on the risk of rupture of untreated cerebral aneurysms were included. Two investigators extracted data on patient age, sex, hypertension, smoking, family history of subarachnoid hemorrhage, aneurysm size, and arterial location.

    Results: From the 7,162 studies identified in the initial search, 406 studies were obtained in full and 9 met inclusion criteria. A total of 9,111 patients with 11,543 aneurysms were included, who were followed for 25,642 patient years. Study populations were from North America, Europe and Japan. The mean age of patients enrolled was 60.4 years and 68.4% were female. The overall annual rupture rate was 0.8%. Univariable meta-regression analysis identified aneurysm size greater than 7mm, male sex, and Finnish or Japanese study population as significantly associated with increased risk of rupture (p=0.04). However, in multivariable meta-regression, only size larger than 7mm remained independently associated with aneurysm rupture (p=0.002).

    Conclusions: In this study-level meta-analysis of prospective, longitudinal studies, the annual rupture rate of cerebral aneurysms was 0.8%. However, the only independent predictor of subarachnoid hemorrhage was aneurysm size greater than 7 mm.

    Patient Care: The appropriate management of unruptured intracranial aneurysms ultimately depends on whether the risk of rupture outweighs the procedural risks of microsurgical clipping or endovascular occlusion. This study provides additional information on the natural history of intracranial aneurysms, which will aid in the assessment of the risk of aneurysm rupture and improve patient care.

    Learning Objectives: By the conclusion of this session, participants should be able to: 1) describe the importance of characterizing the natural history of intracranial aneurysms, 2) discuss putative risk factors for the rupture of intracranial aneurysms, and 3) identify factors that particularly worrisome for aneurysm rupture.


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