Tannic acid-glutaraldehyde fixative and pleomorphic adenomas of the salivary gland: an ultrastructural study.

Four cases of pleomorphic adenomas of parotid glands were fixed by immersion in a mixture of 4% tannic acid and 3% glutaraldehyde followed by OsO4 postfixation and heavy metals staining. This clearly visualized the presence of dense amorphous elastic fibers in cellular and myxochondroid areas. The dense amorphous fibers were associated with varying numbers of peripheral filaments which appeared sometimes as bundles of parallel fibrils without intermingled amorphous material. These intermediate-sized filaments were seen indirect continuity with similar intracellular filaments with or without interposition of basal-membrane-like material and/or with extracellular filament-containing vesicles. It is suggested that these filaments are synthesized intracellularly and released into the extracellular space by neoplastic myoepithelial cells mainly by cytoplasmic vesicle separation. In addition, small round vesicles with a dense core of amorphous material and staining characteristics identical to those of extracellular elastin were frequently seen in the peripheral parts of these myoepithelial-like cells. It is possible that these dense-cored vesicles have a secretory function and contain a precursor of elastin.