INNV-61. CNS germinoma shows reduction in enhancement with steroid monotherapy, emphasizing the importance of a tissue diagnosis

BACKGROUND CNS germinoma is typically treated with combination of chemotherapy and radiotherapy, with steroids used temporarily for symptom management. METHODS We report a case of CNS germinoma initially treated with steroid monotherapy with reduction in radiographic enhancement. RESULTS A 25 year old male initially presented with polydipsia and polyurea that improved with desmopressin, consistent with central diabetes insipidus. Brain imaging was unremarkable and he was lost to follow up. 3 years later, he developed progressively worsening bitemporal scotomas, intermittent binocular horizontal diplopia, reduced visual acuity, headaches, weight gain, and sexual dysfunction. MRI brain revealed enhancement of the pituitary stalk, optic chiasm and optic nerves, floor of the third ventricle, lateral ventricles, periventricular white matter, and anterior corpus callosum and fornix with associated T2 hyperintensity within the optic chiasm and adjacent brain parenchyma. Biopsy was consistent with germinoma. He was started on a dexamethasone taper beginning at 4 mg every 6 hours and plateauing at 4 mg twice daily. 3 weeks after steroid initiation, the areas of enhancement surrounding the frontal horns of the lateral ventricles showed reduction in size. DISCUSSION Reduced tumoral enhancement with steroid monotherapy is a well-known phenomenon in CNS lymphoma and has been reported in gliomas, attributed to direct induction of apoptosis in CNS lymphoma and alterations in the blood brain barrier via suppression of vascular permeability factors in both. This case adds to the scant literature regarding change in enhancement patterns with steroid monotherapy in CNS germinomas, which is likely related to a reduction in tumoral diffuse lymphocyte infiltration with steroid administration. The reduction in enhancement seen in multiple CNS mass-like pathologies emphasizes the importance of a tissue diagnosis for germinomas, as this steroid response is transient and not indicative of true tumor regression. Definitive treatment of germinomas is combination chemotherapy and radiation.