Maxillofacial fibro-osseous lesions: classification and differential diagnosis.

A large diversity of lesions may involve the maxillofacial bones. Some occur exclusively at this site. Other lesions at this location have features that are different from similar lesions occurring elsewhere in the skeleton. This site-dependent morphology applies especially to fibro-osseous lesions, which will be discussed in this report. Fibrous dysplasia shows evenly distributed islands of woven bone that fuse with surrounding bone. The presence of lamellar bone and osteoblastic rimming does not contradict that diagnosis as they would for lesions occurring outside the maxillofacial bones. Ossifying fibromas are demarcated or encapsulated. They show a broad variation in mineralized material that may be woven bone as well as lamellar bone or may be present as rounded cell-poor particles regarded as a form of cementum. Specific subtypes are juvenile ossifying fibroma and psammomatoid ossifying fibroma, both of which contain cellular stroma exhibiting mitotic activity. Lesions known as periapical cemental dysplasia can be found in the tooth-bearing jaw area and are similar to ossifying fibroma but without demarcation. These lesions may be focal, involving one or a few adjacent teeth; when they are more widely distributed, they are named florid cemento-osseous dysplasia. Periapical cemental dysplasia should be distinguished from cementoblastoma, a lesion similar to osteoblastoma but connected with tooth apices. Ossifying fibroma may resemble well-differentiated osteosarcoma as ossifying fibroma may be more cellular and may have a higher number of mitoses than osteosarcoma.