Some ultrastructural features of acinic cell carcinoma.

The ultrastructure of an acinic cell carcinoma, occurring in the left parotid gland of a 52-year-old woman and causing a total facial nerve paralysis, is described. Histologically the tumour consisted of numerous granulated cells arranged around lumen-like openings and resembling a secretory system. Furthermore, areas with agranulated cells growing in a solid pattern were also encountered. In the electron microscope the cytoplasmic granules of the tumour cells displayed a varied appearance. Granules of a dense homogeneous type, as well as granules with a more electron lucid appearance were observed. Furthermore, numerous cytoplasmic granules displayed a bipartite structure with a dense central and a more electron lucid outer zone. In specimens primarily fixed in OSO4 or KMnO4 the granules displayed a 'leached out' appearance. The membrane-bounded of the tumour cells also showed a strong positive staining with the periodic acid-chromic silver technique of Rambourg et al. (1969). Other characteristic ultrastructural features of the tumour cells studied were: Smooth cell surfaces, the presence of subplasmalemmal bands of electron dense material, desmosome-like attachment areas between cells and grossly altered mitochondria.