Primary intracranial germ cell tumors are rare neoplasms that typically affect children and teenagers.
TABLE 1.10 WHO Classification: Intracranial Germ Cell Tumors
Germinoma Embryonal carcinoma Yolk sac tumor Choriocarcinoma Teratoma Mature Immature
Teratoma with malignant transformation Mixed germ cell tumors
They are analogous to their gonadal and extragonadal systemic counterparts and arise almost exclusively in the midline, affecting the pineal and sellar regions, third ventricle, and hypothalamus [24,25]. Several histologic varieties of germ cell tumor are recognized by the WHO and are listed in Table 1.10, including germinomas, embryonal carcinomas, yolk sac tumors, choriocarcinomas, and teratomas. All of these tumors are considered malignant (i.e., WHO grade IV) except for teratoma, which has a more benign histology and clinical course. Germinomas are the most common of all germ cell tumors and are composed of uniform cells resembling primitive germ cells, with large vesicular nuclei, prominent nucleoli and clear, glyco-gen-rich cytoplasm (see Fig. 1.19) . The tumor cells are present in monomorphous sheets or lobules.
Mitoses are plentiful but necrosis is uncommon. Also, delicate fibrovascular septa infiltrated by mature lymphocytes are a common feature. Analysis by immunohistochemistry typically demonstrates posi-tivity for placental alkaline phosphatase. However, patchy positivity for beta-HCG and human placental lactogen can be observed.
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