Clinical features of giant hybrid ameloblastoma of the mandible: a case report with long-term observation of natural growth before treatment

Hybrid ameloblastoma comprising desmoplastic and solid type ameloblastoma with classic follicular or plexiform pattern is a known unusual variant. Ameloblastoma, including the hybrid type, is a slow growing tumor, and there is very little information regarding growth of such tumors when left untreated. We present here the clinical features of a giant hybrid ameloblastoma of the mandible together with extended radiographic observation before the patient consented to surgery. A 62-year-old Japanese man was referred in 2002 with a chief complaint of a left-sided mandibular swelling. Panoramic X-ray showed a multilocular radiolucent lesion extending from the left mandibular angle to the ascending ramus, including an impacted wisdom tooth with root resorption. Biopsy specimen examination revealed myxofibrous tissue with some odontogenic epithelial nests. The clinical diagnosis was odontogenic myxoma or myxofibroma of the left side of the mandible. At that time, the patient declined surgical treatment. The tumor gradually increased in size over 7 years of follow-up, and he finally consented to undergo surgical treatment when the tumor began approaching the skull base. Tumorectomy including hemimandibulectomy and plate reconstruction of the mandible were performed in 2009. Histopathology revealed follicular and desmoplastic ameloblastoma with myxomatous change and was diagnosed as hybrid ameloblastoma. No recurrence was seen at the 24-month follow-up examination, and mandibular reconstruction using bone regeneration and oral rehabilitation with a dental implant were performed. Further clinicopathological analysis of coexisting desmoplastic ameloblastoma and non-desmoplastic ameloblastoma is needed to understand the significance and biological behavior of this hybrid variant.