Germ cell tumors affecting the nervous system include germinoma, yolk sac tumor, embryonal carcinoma, choriocarcinoma, teratoma, and mixed germ cell tumors.
Germinoma is histologically characterized by the presence of large primordial germ cells with prominent nucleoli and variable cytoplasmic clearing. Biphasic population of larger germinoma cells and mature lymphocytes is typical.
Yolk sac tumor consists of primitive-appearing epithelial cells—putatively representing yolk sac endoderm. The cells are arranged in a meshwork of irregular tissue spaces, i.e., reticular pattern.
Embryonal carcinoma is an aggressive non-germinomatous malignant germ cell tumor characterized by large epithelioid cells with enlarged nucleoli and abundant clear to violet cytoplasm resembling those of the embryonic germ disc.
Choriocarcinoma is an aggressive non-germinomatous malignant germ cell tumor composed of syncytiotrophoblasts, cytotrophoblasts, and occasionally intermediate trophoblasts.
Teratoma is a germ cell tumor composed of somatic tissues derived from two or three of the germ layers (i.e., the ectoderm, endoderm, and mesoderm). Mature teratoma (fully differentiated, adult-type tissue elements), immature teratoma (incompletely differentiated elements resembling fetal tissues), and teratoma with malignant transformation (containing intracranial germ cell tumors and can include a variety of somatic-type cancers) are distingushed.
Pathogenetic mechanisms include elevated circulating gonadotropin levels (tumors localized to diencephalic centers regulating gonadal activity), chromosome X overdosage (increased incidence of tumors in Klinefelter syndrome), neoplastic offspring of primordial germ cells that migrate in aberrant fashion or home to the embryonic CNS rather than the developing genital ridges, displaced embryonic tissues misincorporated in the developing neural tube, and toti- or pluripotent stem cells with selective genetic programming along germ cell differentiation and subsequent neoplastic transformation.
Surgical resection is the treatment of choice followed by adjuvant chemotherapy and radiotherapy (germinoma). Outcome is variable. Germinoma is less malignant than choriocarcinoma, prone to recurrence and remarkably radiosensitive. Immature teratomas might undergo spontaneous differentiation into fully mature, somatic-type tissues over time. Mature teratoma is potentially curable. Poor prognosis is present for yolk sac tumor, embryonal carcinoma, choriocarcinoma. Disease progression characterized by local recurrence and CSF-borne dissemination.
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