• Toshikazu Kimura, Chikayuki Ochiai, Kensuke Kawai, Akio Morita, and Nobuhito Saito.
• 1Department of Neurosurgery, Japanese Red Cross Medical Center, Shibuya-ku, Tokyo.
• J. Neurosurg. 2020 Apr 1; 132 (4): 106210671062-1067.

ObjectiveTo investigate the risk of bleeding from unruptured cerebral aneurysms (UCAs), previous studies have used Kaplan-Meier analyses without treating the definitive treatment as a competing risk event, which may underestimate the rupture rate. The authors analyzed the survival of patients with UCAs alongside the occurrence of aneurysm bleeding and its competing risk events.MethodsA retrospective analysis was conducted on 722 patients diagnosed with UCAs in the period from 2000 to 2009 using an institution's electronic medical records and telephone interviews. The cumulative incidence of aneurysm rupture was examined, and factors contributing to rupture were assessed using regression analyses.ResultsBy 2014, 19 patients had experienced aneurysm rupture, with an overall rupture rate of 0.57% per year over 3320.8 person-years. However, cumulative incidence analysis indicated that 1.3% of all patients had a rupture within 2 years after aneurysm identification, and 38.4% of the patients underwent definitive treatment in the same period. Among the patients who experienced rupture, regression analysis revealed that an aneurysm size greater than 5 mm, a location in the anterior or posterior communicating arteries, and an irregular shape contributed to aneurysm rupture, with HRs of 4.4 (95% CI 1.2-15.7), 3.5 (95% CI 1.4-8.7), and 2.1 (95% CI 0.7-6.0), respectively.ConclusionsRupture rate analyses using the person-year or standard Kaplan-Meier method are not as informative without consideration of the competing risks. The incidence of aneurysm rupture should be presented clearly with those of competing risks.

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