Pathology of intracranial germ cell tumors.

Intra cranial germ cell tumors (GCTs) usually arise in midline structures, including the pineal or suprasellar regions of children and young adults. The classification of GCTs includes germinoma, teratoma, yolk sac tumor, embryonal carcinoma, and choriocarcinoma. However, intracranial GCTs are often of mixed histologic composition (mixed GCTs), and only germinoma and teratoma are likely to be encountered as pure tumor types. Although GCTs are usually identified using conventional histological techniques, immunohistochemical studies are very useful for delineating these entities, using special markers such as human chorionic gonadotropin, alpha-fetoprotein, human placental alkaline phosphatase, cytokeratin, as well as c-kit and OCT4. Ultrastructural examination is also useful in confirming the identity of these tumors. Genetic alterations specifically encountered in central nervous system GCTs are largely unknown. Patients with Klinefelter syndrome or Down syndrome appear to be predisposed to the development of gonadal as well as intracranial germinomas. Frequent imbalances of chromosomes have been described in intracranial GCTs, including chromosomes 1, 8, 12, 13, 18 and X. Recently, p14 and c-kit gene alterations have been reported, particularly in some intracranial germinomas; however, their importance remains unclear.