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Many cases of spontaneous occlusion of the circle of Willis (moyamoya disease) have been reported in Japan, but the worldwide distribution is unclear. The total number of cases in each country reported in the literature and complications were evaluated. A total of 1063 cases have occurred worldwide excluding Japan. Cases were observed most frequently in Asia and in people of non-Caucasian origin.
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Goto et al. (1992) studied this question.
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