Ameloblastic fibroma is a tumor in which both the epithelial component and stroma are neoplastic. It is rare: only 122 cases had been reported by 1997. Clinicians and pathologists should be aware of this tumor to avoid confusing it with ameloblas-toma. It is found almost exclusively in the first two decades of life; the average age is 14 years. Almost 70% are found in the posterior mandible. It is not unusual for this tumor to interfere with formation and eruption of teeth, a finding in approximately 75% of patients. Painless swelling or failure of teeth to erupt calls attention to the tumor. Small lesions less than 4.0 cm may be unilocular but larger tumors are more often multi-locular. The microscopic features are characterized by small islands and cords of epithelium growing in an ectomesenchymal stroma that resembles primitive dental pulp tissue. The peripheral epithelial cells may be columnar and exhibit reverse nuclear polarity but there is little tendency to form stellate reticulum-like tissue. Stromal hyalinization adjacent to the epithelium is presumed to be an inductive effect but hard tissue is not formed in this tumor. A granular cell variant of amelo-blastic fibroma exists in which the ectomesenchymal element is converted to eosino-philic, granular cells. Additionally, there is a malignant version, the ameloblastic fibrosarcoma. In this tumor, the ectomesenchyme assumes the cytologic characteristics and behavior of a sarcoma. More than 50 cases have been reported. The amelo-blastic fibroma is not encapsulated but local infiltration is minimal. Most are cured by thorough enucleation. A recurrence rate of 18% has been reported.
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