Cystic cemento-ossifying fibroma of the ethmoidal cells (a case report).

A case report of an aggressive cystic cemento-ossifying fibroma of the ethmoidal cells is presented. Fibro-osseous lesions containing cementum are considered to be of periodontal membrane origin and are most common in the mandible and maxilla. Following the WHO classification, fibro-osseous lesions containing cementum are grouped together under the heading of cementoma and are divided into four subgroups. Cemento-ossifying fibroma is considered to be a variant of cementifying fibroma which is a sub-group of cementoma. The unique site of origin seen in this case is thought to have been the result of an ectopic periodontal membrane or of a primitive mesenchymal cell rest or incomplete migration of the medial part of the nasal anlage and differentiation into the periodontal membrane.