title: Pleomorphic adenoma, II: Ultrastructural organization of "stromal" regions.
abstract: Findings from an ultrastructural study of 24 major and minor salivary gland pleomorphic adenomas suggest that the principal cell type in the myxoid and chondromyxoid regions of these tumors is a structurally modified myoepithelial cell. This interpretation is based on findings in the transitional zone between myxoid regions and compact cellular areas that have a ductal-acinar organization, that is, are composed of luminal epithelial and modified myoepithelial cells. Survey-type low-power electron micrographs allowed appreciation of the original orientation of the major proliferating component of these tumors to the perimeter of ductal-acinar units. The low-power electron micrographs also revealed residual features of this organization, the early development and subsequent sequential alteration of matrix compartments as tumor cells became increasingly separated by extracellular products, and a variety of myoepithelial cell modifications, such as squamous and chondroid metaplasia, resulting from neoplastic induction. According to the authors' interpretation, modified myoepithelial cells in myxoid and chondromyxoid regions form a continuum with similar tumor cells in transitional and solid areas, forming what can be visualized as markedly expanded and merging ductal-acinar units that tend to converge with similarly altered adjacent neoplastic ductal-acinar units. Thus, a multiplicity of processes are involved in the formation of the complex and varied histologic patterns that characterize pleomorphic adenomas.
mesh_terms: D008949:Adenoma, Pleomorphic / Q000648:ultrastructure*; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010307:Parotid Neoplasms / Q000648:ultrastructure*; D010873:Pinocytosis