GCT-55. INTRACRANIAL GERMINOMA ORIGINATING FROM ATYPICAL LOCATION WITH SUBCLINICAL ADH INSUFFICIENCY

INTRODUCTION: Intracranial germinomas are rare tumors which usually develop in the midline structures and affect in 90% of cases the pineal gland and suprasellar regions. Sometimes they involve basal ganglia, septum pellucidum, and other regions. We report a very unusual presentation of an intracranial germinoma originating from the lateral ventricle. METHODS: A 10-year-old boy presented with a 1-year history of polydipsia and polyuria. During the hypertonic saline test, a low ADH was detected and established the diagnosis of subclinical ADH insufficiency. MRI showed a heterogeneously enhancing periventricular lesion in the lateral ventricle, but no other abnormal findings, including hypophyseal stalk. Initially, the correlation of imaging findings and clinical symptoms were not clear. With suspected subependymoma, tumor removal was performed by small craniotomy. Since the intra-operative pathological diagnosis was germinoma, we performed only partial removal of the tumor. After establishing the histological diagnosis of germinoma, the patient received chemotherapy using carboplatin and etoposide, followed by radiation therapy. MRI showed no recurrence for five years after treatment. RESULTS/ CONCLUSION: Our case presents two atypical features. First, intracranial germinoma originating from the lateral ventricle is quite rare. Though the cases with intracranial germinoma originating from septum pellucidum and corpus callosum have been reported, this case is even different. Second, imaging findings did not match clinical symptoms. The cause of subclinical ADH deficiency may be the occult hypophyseal germinoma. In conclusion, we report a 10-year-old case with a very unusual presentation of an intracranial germinoma originating from the lateral ventricle.