Primary midbrain cystic germinoma mimicking glioma: a case with neuroendoscopic biopsy.

Intracranial germinoma arising primarily in the midbrain is extremely rare. We present the first reported case of cystic midbrain germinoma that lacked evident solid components and mimicked a midbrain glioma. In a 22-year-old man with headache and diplopia, magnetic resonance imaging showed a ring-enhancing lesion in the midbrain. The preoperative diagnosis included brain stem glioma, metastasis, and neuroepithelial cyst. A neuroendoscopic biopsy specimen provided a histologic diagnosis of germinoma. The patient responded well to chemotherapy and radiotherapy. The case illustrates the diagnostic value of neuroendoscopic biopsy in the differential diagnosis of brainstem lesions in adult. The possibilities considered should now include germinoma.