Calcifying Cystic Odontogenic Tumor Associated with a Complex Odontoma

We present a case of a 16-year-old lad with a one year history of gingival mass of the left maxillary alveolar ridge. Excision revealed a cystic mass with brown fluid and irregular calcified material within the cavity. Histopathologic examination of the cyst lining shows a stratified cuboidal epithelium with palisading of the basal layer. The cells of the latter show reverse nuclear polarization reminiscent of ameloblastic epithelium. The superficial layers have a stellate reticulum-like appearance and contain large eosinophilic polygonal ghost cells. (Figure 1, 2) Some of the ghost cells show calcifications. (Figure 3) Sections from the hard, bony fragments show haphazard deposition of dentin and enamel-like material. (Figure 4) With these features, this case was called a calcifying cystic odontogenic tumour in association with a complex odontoma. Calcifying cystic odontogenic tumor (CCOT) is a benign neoplasm characterized by an ameloblastoma-like epithelium with ghost cells that often show calcification.1 It comprises only 2% of all benign odontogenic neoplasms.2 There is equal distribution of involvement for the maxilla and mandible, no sex predilection, with most cases diagnosed at the 2nd to 3rd decade of life.1,2 The classic histologic findings are the presence of a stratified epithelium consisting of cuboidal to columnar cells with reverse polarization of the basal layer and the presence of ghost cells. A stellate reticulum-like appearance of epithelial cells is also seen. Ghost cells are the most characteristic feature of CCOT and this may represent an abnormal type of keratinization or the coagulative necrosis of the odontogenic epithelium. 3 CCOT may present alone or in association with other odontogenic tumours.2, 4 Association with an odontoma has been reported in 20% to 24% of cases of CCOT.5 Complex odontoma is a hamartomatous lesion characterized by haphazard arrangement of matrix-producing epithelium, enamel, dentin and cementum-like tissue, in contrast to the more regular structure of a compound odontoma.1 CCOT associated with odontoma (CCOTaO), in contrast to CCOT alone, has a slight female predominance (2:1), a younger age of presentation (mean 16 years) and a predilection to the maxilla (61.5 %).5 Sidana et al. postulated several possible pathogenesis of CCOTaO including the possibility that CCOT develops secondarily from the epithelium involved in the formation of odontoma or that the odontoma develops secondarily from the epithelium in CCOT.5 Enucleation is the treatment of choice and is curative. A close histologic differential diagnosis is an acanthomatous ameloblastoma. Acanthomatous ameloblastoma contains distinct squamous epithelium within nests of ameloblastic epithelium, and ghost cells are absent. Very rarely, transformation into its malignant counterpart, ghost cell odontogenic carcinoma (GCOC), has been reported in recurrent cases.6, 7 Infiltrative borders, nuclear atypia and increased mitotic activity indicate this change.6, 7