Ameloblastoma and keratinizing ameloblastoma in dogs.

Ameloblastomas reviewed in this report were locally invasive neoplasms arising from the epithelial structures of the dental lamina, and were characterized histologically by features which are unique to dental lamina epithelium. These include the formation of epithelial sheets in which the cells nearest the stroma form a palisading row aligned perpendicularly to the basement membrane and the cells toward the center separate from each other except at desmosomal attachments. This is similar to the appearance of th stellate reticulum of the early enamel organ. Other features include epithelial cords which branch and interconnect, and the intimate association of epithelial structures and collagenous matrix. In our dogs, other important features were the deposition of inclusions similar in appearance to enamel matrix between the cells of the epithelium and various degrees of keratinization. All ameloblastomas studied were locally invasive tumors which occurred at various sites on the gingiva. The average age of the dogs was 8.7 years and the age range was three to 13 years. Radiographically, all of the tumors studied resulted in periodontal osteolysis. Six dogs were treated with radiation therapy, but details of the radiotherapy of two dogs could not be located. Of the other four dogs, one is alive 48 months after radiotherapy with no evidence of tumor regrowth. Regrowth of the oral tumor was apparent in the other three dogs six, 21, and 34 months after completion of the radiotherapy. Three dogs were treated by radical mandibulectomy; all are alive with no evidence of tumor recurrence at two, 20, and 28 months postoperatively. Two dogs had local dissection (curettage) of tumors and the tumors recurred at 12 and 15 months after surgery. One dog was euthanatized after diagnosis of the oral tumor because of a progressive neuropathy.