LAUSR

A 12-year-old boy was admitted to the hospital because of a 2-month history of dizziness and nausea. The neurological examination was unremarkable. Brain magnetic resonance imaging (MRI) revealed a multicystic lesion comprising multiple similar round cystic spaces located at the third ventricle and the frontal horns of both lateral ventricles (Fig A, B). The cystic cavity exhibited hypointense signal on T1-weighted and hyperintense signal on T2-weighted images relative to the brain parenchyma, and decreased signal intensity on diffusionweighted images. The signal of the cystic wall was isointense with that of the gray matter on T1and T2-weighted images, and slightly contrast-enhanced following administration of gadolinium. Whole-spine MRI did not reveal any metastases. Blood tests showed a normal α-fetoprotein level of 3.91 ng/ml (normal range, 0–20 ng/ml) and slightly increased β-human chorionic gonadotropin level of 13.31 mIU/ml (normal range, 0–10 mIU/ml). The patient developed worsening headache and vomiting within 5 days after admission. The repeat MRI performed 2 weeks after the initial examination demonstrated expansion of the cystic lesion and progressive hydrocephalus (Fig C, D). Stereotactic tumor biopsy was subsequently performed. Histopathologic examination revealed germinoma and immunohistochemical staining demonstrated that the tumor cells were positive for octamer-binding transcription factor 4 and CD117. The Ki-67 labeling index was 30%. The patient was started on radiotherapy with a prescribed radiation dose of 40 Gy/20 f and chemotherapy with temozolomide and irinotecan. Brain MRI performed at the 41-month follow-up revealed significant reduction of the tumor and no evidence of local recurrence or distant metastasis (Fig E, F). Intracranial germinomas are rare and sensitive to radiation therapy and chemotherapy; therefore, accurate imaging diagnosis is crucial. The main distinguishing radiological feature of germinomas relates to their typical sites of involvement; these tumors are usually found in midline structures, most commonly the pineal and suprasellar regions. Other sites of origin, such as the basal ganglia, cerebellum, and brainstem, have been rarely reported. A review of the English literature demonstrated only few reported cases of germinoma in the ventricular system, with the majority having occurred in Asian countries. In a retrospective study on the MRI characteristics of germinomas, all tumors had solid components, with intratumoral cysts seen in some of them. The cysts could be single or multiple, polycystin-like or honeycomb-like, which was recognized as a rare but very characteristic clinical sign. The present case was unique in that the tumor showed diffuse subependymal involvement of the lateral and third ventricles and had characteristic appearance of multiple similar cysts lacking a solid component. Understanding disease-specific imaging features may improve diagnostic considerations. As such, germinomas should be included in the differential diagnosis of infiltrative parenchymal lesions invading the ventricular system, particularly those seen among adolescents and young adults.