Dental Germ Tumor: An Unusual, Cystic, Mixed Epithelial-Mesenchymal Odontogenic Tumor.

Although odontogenic lesions have been extensively described and studied, anomalous, challenging cases occasionally come to the attention of the pathologist. Here, we report the clinical and microscopic characteristics of an unusual cystic lesion of odontogenic origin. A 16-year-old male presented with swelling and pain to palpation of the right mandible as well as numbness of the right lower lip. Radiographically, the corresponding lesion was well-defined and radiolucent with internal radiopaque foci. It extended from the right first premolar posteriorly, approaching the angle of the mandible, and involved the mandibular first molar which was impacted and displaced. The second and third right mandibular molars were also impacted and displaced. The patient was treated by excisional biopsy under general anesthesia. The histopathologic examination revealed the presence of multicystic areas lined by a thin, non-keratinizing squamous epithelium that resembled the epithelial lining of a dentigerous cyst. In continuity with the cystic lining, areas of myxoid tissue reminiscent of dental papilla were observed. The myxoid tissue formed structures that were surfaced by an epithelium comprising a basal layer of ameloblast-like cells with reverse polarity of the nuclei. Above the basilar cells, additional layers of epithelial cells composed a structure resembling the enamel organ. Subjacent to the basilar ameloblast-like cells, a condensation of mesenchymal cells with polarized nuclei opposite to the ameloblast-like cells was present. These mesenchymal cells resembled odontoblasts. In addition, numerous mineralized structures amongst the odontogenic epithelial tissue were present. To date, the patient remains well and without evidence of recurrence after 36 months of follow-up.