Ultrastructure of three histologic variants of the ameloblastoma

Abstract

T h e ultrastructural features of a follicular ameloblastoma, a cystic ameloblastoma, a n d a pseudoglandular ameloblastoma are examined. Although common origin from oral epithelium is evidenced by the presence of tonofilaments a n d desmosomes in every specimen, variations are prominent among the different tumors. Findings which indicate that differentiation toward odontogenesis may he more advanced in this neoplasm than is generally accepted include: polarization of nuclei a n d 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 a n ameloblastoma appears to result from stromal degeneration, expansion of intercellular space within epithelial islands, and breakdown of epithelial cells. HE SIMPLE AMELOBLASTOMA IS A NEOPIASMT generally considered to be related to tooth germ epithelium but of insufficient differentiation to allow for actual formation of calcified tissues. Although this tumor histologically resembles the enamel organ, different cases and even different areas within tlie same lesion show wide microscopic variation. These differences have been likened to the morphological stages of odontogenesis.ll.14 1~5Most ameloblastomas, notwithstanding focal diversity within a given tumor, tend to show a predominant microscopic pattern; thus sever a 1 his t o m or p h o 1 og i c s u b c 1 asses have been proposed. Among these ale plexiform, follicular, papilliferous, primitive, acanthomatous, pseudoglandular, ~ystic, 1 ascular, mucoepidermoid, basal cell, and gi anular cell ameloblastomas. 5z1* ~4 2 3~7 T h e present study is an ultrartructural examination of three simple ameloblastomas which differ in basic histologic pattern.

Ultrastructure of ameloblastoma and its variants

“…[18] Mucin-producing cells were reported by Mincer and McGinnis to occur in a multicystic ameloblastoma. [19] The discovery of these cells had earlier led Hodson to propose a subclass of mucoepidermoid ameloblastoma. [12] The occurrence of intracytoplasmic desmosomes in a maxillary ameloblastoma was reported by Cutler.…”

“…The cells of the follicular type contained many lysosomes, whereas plexiform cells consisted of numerous vacuoles and tonofilament bundles joined by desmosomal attachment which mimics squamous epithelium [ Figure 2f and g]. [19] The connective tissue stroma constitutes of stellate cells and fibers. The cytoplasm showed RER, Golgi apparatus, and swollen mitochondria [ Figure 2h].…”

“…Studies done by Mincer and McGinnis [19] had described cystic lumen which was lined by squamatoid epithelial cells having a foamy, basophilic cytoplasm which contained relatively few organelles. These individual cells among the lining epithelium which at the light microscopic level resembled mucin-producing cells.…”

“…Ultrastructurally, Mincer and McGinnis [19] had studied a case where the cells were in close approximation with each other and showing minimum intercellular spaces. They also demonstrated numerous osmiophilic autophagolysosomes (cytosegrosomes).…”

“…[29] Conclusion Ameloblastoma is a rare OT with histomorphologic diversity. There are very few reports available on ultramicroscopy regarding [19] …”