No abstract

Only three previous reports on the ultrastructural appearance of tibial adamantinoma have been found among some 120 cases of this tumor reported in the literature. The tumor in our case is less differentiated than the cases previously reported. We believe it is of epithelial character and the possibilities of its histogenesis have been narrowed down to either mesothelial, synovial or squamous origins among the many theories proposed. Ameloblastic origin, however, cannot be ruled out.

The fine structure of a pineal germinoma was studied in tissue blocks and in tissue culture. The original tumor contained large primary tumor cells, lymphocytes, macrophages, plasma cells, and astrocytes. The large primary tumor cells were characterized by large nuclei, relatively scanty organelles, abundant glycogen, and junctional complexes. The neoplasm grew well in vitro and, with the exception of plasma cells, contained the same cell types found in vivo. The ultrastructural characteristics of the cells in vivo and in vitro were similar. In culture there were few large primary tumor cells. Macrophages, often involved in active phagocytosis, were prominent in the original tumor and were the most common cell type found in vitro. A tumor‐associated immune response is postulated in this neoplasm.