single bone depending on the period of mutation; contraction by multiple lesions 3) , and; case accompanying endocrinopathy 4) . About 80~85% of fi brous dysplasia cases have the type of monostotic contraction and usually develop during the teenage years. It occurs in both males and females, although females tend to record a higher incidence rate these days. Generally, when it occurs in the jawbones, the rate is double in the maxilla than that in the CASE REPORT Fibrous dysplasia is a benign fi

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... bro-osseous lesion wherein normal bone is replaced with an excessive proliferation of cellular fibrous connective tissue intermixed with irregular bony trabeculae. Fibro-osseous lesions like fibrous dysplasia are often associated with non-epithelial cysts, such as simple bone cyst. The etiologic and pathogenic relationships between fi brous dysplasia and simple bone cyst have not been conclusively established. Nonetheless, the mechanism of cyst formation in fibro-osseous lesion associated with simple bone cyst can be said to differ from that of the typical simple bone cyst of the jaws. This article reports a case of bilateral lesions including fi brous dysplasia and simple bone cyst on each site and reviews the pathogenesis of cyst formation in the fibro-osseous lesion.