The central nervous system is one of several extragonadal sites of presentation of germ cell tumors. Yolk sac tumor is a nongerminomatous germ cell tumor, also known as endodermal sinus tumor (14). Germ cell tumors originated in embryonic germ cells, that were evolved pluripotent stem cells and embryonal carcinoma stem cells, further formed embryonal carcinoma, choriocarcinoma, yolk sac tumor and teratoma (6, 15).
Yolk sac tumor was the product of pluripotent stem cell differentiation in the extraembryonic structure, and characterized by abnormal development of mesoderm in the embryo and endoderm in the yolk sac. The tumor texture was firm, with hemorrhage and necrosis, and could be local infiltration, or spread along the subarachnoid space, and also along the VP shunt tube planted into the peritoneal cavity (16, 18). Yolk sac tumor cells are undifferentiated epithelial cells of the primitive endodermal sinus, arranged in irregular labyrinthine-like adenoid structures, often formed micro-cystic or cribriform. The glomerular-like structures formed by tiny blood vessels, which covered single layer of cubic cell, can be seen protruded into the cavity consisted of flat cells. Schiller-Duval bodies, formed by tubulopapillary sinusoidal structures with central vascular core and cuboidal to columnar epithelial-like cell lining, as well as cytoplasmic and extra-cellular eosinophilic globules are diagnostic features (6, 16).
The majority of locations are near the midline, such as the saddle and pineal region, basal ganglia and the thalamus (24, 4, 12), a few may occur in the lateral ventricles, third ventricle, cerebral hemispheres or brainstem (1, 19, 25). The imaging diagnosis of intracranial germ cell tumors in typical regions are more clear, but in rare site are easily misdiagnosed. The appearance of yolk sac tumours demonstrated a variety of imaging features, usually with heterogeneous enhancement (20, 23, 3). In this case the tumor located in the right cerebellar hemisphere, occurred in a two years old boy. It was difficult to distinguish with cerebellum glioma, hemangioblastoma and medulloblastoma. The diagnosis was depending on the combination of elevated AFP and histopathological examination (9, 21).
Tumor markers in intracranial germ cell tumors could be detected in a lot of kinds, including AFP, β-HCG, placenta alkaline phosphatase (PLAP), carcinoembryonic antigen (CEA) and so on. These positive markers indicated the possibility of intracranial germ cell tumors. The efficacy of the treatment of germ cell tumors could be evaluated by the changes of these tumor markers. If AFP and β-HCG elevated or only AFP elevated should be considered nongerminomatous malignant germ cell tumors (9, 21).
Large differences are existed in the prognosis of germ cell tumors. The prognosis of intracranial germ cell tumors are associated with pathology. The prognosis of germinomas and mature teratoma are the best. Pure germinomas could be cured, most literatures reported more than 90% of 5 years survival rate, and more than 80% of ten years survival rate. The prognosis of immature and malignant teratoma and germ cell tumors were poorer. Embryonic carcinoma, choriocarcinoma, yolk sac tumor and mixed germ cell tumor had highest malignant degree and the worst prognosis (17). Matsutani et al. reported the 3 years survival rate of germinomas was 70%, but much lower of nongerminomatous germ cell tumors (10).
There are various reports of current treatment options of intracranial germ cell tumors (7). Germinomas have long been known to be highly curable with both radiotherapy and chemotherapy (2, 5). Nongerminomatous germ cell tumors are benefited from a combination of surgical resection, chemotherapy and radiotherapy (13, 22). However, specific treatment of nongerminomatous germ cell tumors is much less clear. Further multicenter studies are needed to help improve treatment approaches and prognosis.