The purpose of this study was to analyze the management of individual patients with unruptured intracranial aneurysms (UN-ANs) using a decision-analytic approach. Tran sition probabilities among Glasgow Outcome Scale (GOS) categories were estimated from the published literature and data from patients who had been treated at Kitasato University Hospital. Utilities were obtained from 140 health providers based principally on the GOS. Baseline analysis for a healthy 40-year-old man with an anterior UN-AN less than 10 mm in diameter showed that the quality-adjusted life expectancies for preventive operation and follow-up were 15.34 and 14.66 years, respectively. For a follow-up strategy to be preferred, the annual rupture rate had to be as low as 0.9%. These results were sustained through extensive sensitivity analysis. The results sup port preventive operation for UN-ANs, and identify problems that can be clarified with a well-designed stratified clinical trial. Key words: decision analysis; Markov model; unruptured intracranial aneurysms; Glasgow Outcome Scale; utility; preventive oper ations. (Med Decis Making 1998;18:357-364)
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