Odontogenic fibroma is a rare benign mesenchymal tumor, originating from dental papillae, dental follicles, or periodontal ligaments. A 16-year-old boy was referred to our hospital because of swelling of the mandibular gingiva from the left second molar to the right canine. Panoramic and CT images revealed a well-circumscribed, extensive multilocular radiolucent lesion extending from the left third molar to the right second premolar. In addition, root resorption was found from the left second molar to the left canine. The clinical diagnosis was an ameloblastoma, and tumor extirpation was performed under general anesthesia. Histopathological examination of the extirpated specimen showed not the pattern of ameloblastoma, but proliferation of tumor cells with small spindle nuclei and cytoplasm. The lesion was composed mainly of fibroblastic tissue. Immunohistochemical staining was performed with cytokeratin 19, AE1/AE3, EMA, vimentin, CD 34, α-smooth muscle actin, and S-100 markers. Only vimentin was positive. The definitive diagnosis was a central odontogenic fibroma. No evidence of recurrence has been noted during 2 years 8 months of postoperative follow-up.
