Walsh & Hoyt: Germ Cell Tumors

Tumors of germ cell derivation represent five interrelated neoplasms that demonstrate a hierarchic order of increasing malignant behavior: germinoma, teratoma (including immature and malignant forms), embryonal carcinoma, endodermal sinus tumor, and choriocarcinoma. Each represents the malignant correlate of a normal-developing cell type: the primordial germ cell (germinoma), the embryonic differentiated derivative (teratoma), the pluripotential stem cell of the embryo proper (embryonal carcinoma), the extraembryonic differentiated derivatives that form the yolk sac endoderm (endodermal sinus tumor), and the trophoblast (choriocarcinoma). The tumors may occur in ""pure"" form or in different histologic combinations. Sano et al. reviewed 153 cases of intracranial germ cell tumors and found 63% to be monotypic and 37% to be mixed; a similar ratio has been found by others. All of these tumors arise in specific midline sites, primarily in the gonads, sacrococcygeum, retroperitoneum, and mediastinum. The tumors also occur intracranially, usually in the regions of the pineal gland, third ventricle, hypothalamus, or optic chiasm. The light and electron microscopic appearance, as well as the histochemical composition of a germ cell tumor, is specific for each type of tumor, regardless of the site of origin. Thus, a germinoma that originates intracranially has the same histologic and histochemical features as a germinoma that originates in the gonads.