This 14-year-old boy presented with left hemiparesis, gait disturbance, and multiple cranial nerve palsies. Magnetic resonance imaging revealed a multicystic mass with hemorrhagic fluid–fluid levels in the right midbrain, suggesting the presence of a cavernous malformation. Diffusion tensor imaging showed the mass to be close to the right corticospinal tract and ipsilateral medial lemniscus. Subtotal removal of the mass was performed via a right subtemporal approach. The histopathological diagnosis was of a mixed germ cell tumor (GCT) comprising mature teratoma and germinoma cells with syncytiotrophoblastic giant cells. The patient underwent postoperative chemotherapy and radiotherapy, and no tumor progression was found during 1 year of follow-up.
Intracranial GCTs arise mainly in the pineal and the suprasellar area. Germ cell tumors in the brainstem are rare, with only 12 reported cases. Among these, 4 were in the midbrain and histologically were pure germinomas. To the authors' knowledge, this is the first reported case of a mixed GCT in the midbrain combining mature teratoma and germinoma cells.