DISTINGUISHING FEATURES OF FOCAL CEMENTO-OSSEOUS DYSPLASIAS AND CEMENTO-OSSIFYING FIBROMAS .1. A PATHOLOGICAL SPECTRUM OF 316 CASES

Focally expressed cemento-osseous dysplasia (periapical cemento-osseou s dysplasia and focal cemento-osseous dysplasia) and cemento-ossifying fibroma (ossifying fibroma and cementifying fibroma) are two clinical ly recognized entities that are not easily differentiated histopatholo gically because of the lack of recognition of specific microscopic fea tures. We have assessed 20 pathologic parameters for their ability to distinguish reliably between the two. Included in this study were 241 cases of focally expressed cemento-osseous dysplasia and 75 cases of c emento-osseous fibroma diagnosed from a combination of clinical, radio graphic, and histopathologic information. Results revealed that 92.5% of focally expressed cemento-osseous dysplasia were composed of multip le small fragments of tissue whereas 88.0% of cemento-osseous fibromas showed a large intact specimen. Thick curvilinear trabeculae (''ginge r root'' pattern) or irregularly shaped cementum-like masses were typi cally seen in focally expressed cemento-osseous dysplasia, whereas thi n isolated trabeculae with prominent osteoblastic rimming were more co mmonly observed in cemento-osseous fibroma. The stroma of focally expr essed cemento-osseous dysplasia often displayed characteristic caverno us-like vascularity that was almost always associated with bony trabec ulae. Free hemorrhage was frequently interspersed in the artifactual s paces throughout focally expressed cemento-osseous dysplasia. In contr ast, the cases of cemento-osseous fibroma showed more cellularity in t he stroma in which a storiform pattern was present in more than hall t he lesions studied. Giant cells, when present in cemento-osseous fibro ma, were clustered in the center of the cellular stroma. The features described here allowed distinction histopathologically in 94% of cases studied. Three progressive stages of focally expressed cemento-osseou s dysplasia and subtypes oi cemento-osseous fibroma may be recognizabl e microscopically.