Comparative studies of normal and neoplastic ovarian germ cells: 2. Ultrastructure and pathogenesis of dysgerminoma.

A series of dysgerminomas of the ovary was examined by electron microscopy and the findings were compared with germ cells in the normal developing ovary. The ultrastructural characteristics of the neoplastic cells, including prominent reticular nucleoli and sparsely distributed cytoplasmic organelles, indicated a close resemblance to oogonia present in the fetal ovary. Occasional cells had localized collections of glycogen, resembling primitive germ cells, but the irregular ameboid appearance and eccentric nuclear location characteristic of cells in the early stage were not seen. Ultrastructural features of oocyte differentiation, such as synaptinemal complexes and perinuclear arrangement of mitochondria, were not found in any of the tumors. Intercellular bridges, a frequent finding at the oogonial stage in the normal ovary, were absent in all of the tumors. The lack of intercellular communication could be responsible for uncontrolled mitotic division leading to germ cell neoplasia.