Pineoblastoma: an electron microscopic study.

The ultrastructure of a human pineoblastoma is described. Tumor cells formed nests, palisading row and rosettes. Cells within nests were undifferentiated. Palisade and rosette forming cells had polarized cytoplasms and showed signs of differentiation and surface membrane specialization which included surface end-bulb-like protrusions of the cytoplasm, bulbous cilia with a 9 + 0 microtubular skeleton, and blunted microvilli. In the cytoplasm of tumor cells there were characteristic granular bodies, whorls of smooth endoplasmic reticulum and annulate lamellae. Some of these findings appear to be unique to pineal tumor and are reminiscent of photoreceptor cells in the pineal glands of lower vertebrates and human fetal pineal glands.