Ultrastructure of three histologic variants of the ameloblastoma

The ultrastructural features of a follicular ameloblastoma, a cystic ameloblastoma, and a pseudoglandular ameloblastoma are examined. Although common origin from oral epithelium is evidenced by the presence of tonofilaments and desmosomes in every specimen, variations are prominent among the different tumors. Findings which indicate that differentiation toward odontogenesis may be more advanced in this neoplasm than is generally accepted include: polarization of nuclei and mitochondria, “dark” ameloblasts, autophagolysosomes, and a juxtaepithelial component which resembles early enamel or dentinal matrix. Cells similar to mucin-secreting and eccrine elements are also present. One of the tumors contains intranuclear inclusions which resemble papovirus particles. Cyst formation in an ameloblastoma appears to result from stromal degeneration, expansion of intercellular space within epithelial islands, and breakdown of epithelial cells.