Intracranial dysembryogenetic tumors: pathogenesis and their order of malignancy.

Dysembryogenetic tumors can be classified into three main categories: (1) tumors derived from embryonal cell rests in situ such as craniopharyngioma, Rathke's cleft cyst, chordoma, etc., (2) tumors derived from embryonal cells straying into the tissue ("verirrte Keime") such as so-called germ cell tumors, epidermoid, dermoid, lipoma, hamartoma, etc., and (3) included twin (fetus-in-fetu) tumors. The pathogenesis of the second one may be that the embryonic cells of various stages of embryogenesis are misplaced in the bilaminar embryonic disc at the time of the primitive streak formation, becoming involved in the stream of lateral mesoderm and carried to the neural plate area to become incorrectly enfolded into the brain at the time of neural tube formation. The third category of tumor may be related to sequestration of cells of the blastocyst before differential blocking of the genome has occurred. The author propounds the following hypothesis: intracranial dysembryogenetic tumors composed of cells resembling the cells that appear in the earlier stages of embryogenesis are more malignant than those composed of cells resembling those appearing in the later stages of embryogenesis.