Intracranial germ cell tumors

Abstract

Germ cell tumors originating from the gonads may also occur in the central nervous system (CNS). They arise from primordial germ cells that were trapped within neural tissue during the process of migration at the time of early embryogenesis [20]. Intracranial germ cell tumors include six subtypes classified by the World Health Organization: germinoma, embryonal carcinoma, yolk sac tumor (endodermal sinus tumor), cho-riocarcinoma, teratoma, and mixed germ cell tumor, representing diverse directions and various stages of differentiation of germ cells. Aside from the concept by Teilum [20], Sano [18] proposed a hypothesis suggesting each category of germ cell tumors may correspond to the neoplastic equivalent of various kinds of tissue that proliferate and differentiate during embryogenesis. This hypothesis improved understanding of the correlation between the stage in embryogenesis when the normal counterpart cell type of a tumor appears and the malignancy of the tumor [18]. The exact correlation between each subtype and its normal counterpart cell type in embryogenesis, however, is unclear. Teratomas are classified into mature, immature, and teratoma with malignant transformation. Immature teratoma contains embryonal or fetal tissues and is graded by the immaturity and amount of the primitive neuroepithelial elements (glial cells of varying type, neurons, and choroid plexus). Teratoma with malignant transformation contains areas of frank conventional somatic-type malignancy, including adenocarcinoma, squamous carcinoma, or sarcoma. Rhabdomyosarcoma and undifferentiated sarcoma are the most commonly associated sarcomas. Teratoma mixed with other malignant subtypes of germ cell tumors was once called malignant teratoma, but the term is no longer in use to avoid confusion. © 2010 Springer-Verlag Berlin Heidelberg.