ABSTRACT
Primary mixed germ cell tumor is a very rare tumor in the cranial cavity. It is composed of varying combination of germ cell neoplasms, such as germinoma, embryonal carcinoma, choriocarcinoma and teratoma. The authors experienced a case of mixed germ cell tumor developing in the floor of the third ventricle, in a twelve years old boy. He was admitted to the hospital, because of headache, eyeball pain, diplopia and vomiting. Brain CAT scan revealed a round tumor density in the floor of the third ventricle. Tumor marker study, preoperatively checked, revealed beta-HCG, 439.8 mIU/ml and alpha-fetoprotein, under 20 ng/ml. On operation, there was a dark brown firm mass up to 3.0 cm in the third ventricle, that invaded into the foramen Monro. With microscopic examination, this tumor is composed chiefly of germinoma, with embryonal carcinomatous region, choriocarcinomatous region and focal mature teratomatous region. The authors diagnosed this case as mixed germ cell tumor.