Distinguishing features of focal cemento-osseous dysplasias and cemento-ossifying fibromas: I. A pathologic spectrum of 316 cases.

Focally expressed cemento-osseous dysplasia (periapical cemento-osseous dysplasia and focal cemento-osseous dysplasia) and cemento-ossifying fibroma (ossifying fibroma and cementifying fibroma) are two clinically recognized entities that are not easily differentiated histopathologically because of the lack of recognition of specific microscopic features. 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 cemento-osseous fibroma diagnosed from a combination of clinical, radiographic, and histopathologic information. Results revealed that 92.5% of focally expressed cemento-osseous dysplasia were composed of multiple small fragments of tissue whereas 88.0% of cemento-osseous fibromas showed a large intact specimen. Thick curvilinear trabeculae ("ginger root" pattern) or irregularly shaped cementum-like masses were typically seen in focally expressed cemento-osseous dysplasia, whereas thin isolated trabeculae with prominent osteoblastic rimming were more commonly observed in cemento-osseous fibroma. The stroma of focally expressed cemento-osseous dysplasia often displayed characteristic cavernous-like vascularity that was almost always associated with bony trabeculae. Free hemorrhage was frequently interspersed in the artifactual spaces throughout focally expressed cemento-osseous dysplasia. In contrast, the cases of cemento-osseous fibroma showed more cellularity in the stroma in which a storiform pattern was present in more than half the lesions studied. Giant cells, when present in cemento-osseous fibroma, 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-osseous dysplasia and subtypes of cemento-osseous fibroma may be recognizable microscopically.