Don't Drink the Water

Cranial and orbital MRI showed marked evolution of thickening and enhancement of the left optic nerve, diffuse T2 signal change in the white matter including corpus callosum and internal capsule extending through the brainstem, patchy multifocal T2 signal change in the brainstem, evolution of encephalomalacia in the left cerebral peduncle, and contrast enhancement of cranial nerves 3 and 6. Repeat CSF analysis showed 7 oligoclonal bands, an elevated IgG index of 1.0, 2 WBCs, and mild elevation in total protein at 51. CSF cytology and autoimmune encephalopathy panel were negative. Serum AFP was 2.9 (nl <6) and beta HCG 1.2 (nl <1.4). CSF beta human chorionic gonadotropic was 3.5 (nl <1) and AFP was < 0.5. Free thyroxine was 0.8, Testosterone was 270. Prolactin was 17.4 (nl 4-15.2). Morning cortisol was 6.4 (nl 7-25). Desmopressin led to improvement in his polydipsia and polyuria and he was felt to have central diabetes insipidus. Full body positron emission tomography scan that revealed no evidence of fluorodeoxyglucose (FDG)-avid malignancy. There was mild FDG activity associated with the left optic nerve. The next step was to proceed with a tissue diagnosis at the most likely highest yield site with lowest risk - the left optic nerve. The pathologic findings from the left optic nerve biopsy were consistent with germinoma. The nerve was completely replaced by a population of neoplastic cells with large nuclei with prominent nucleoli and abundant pale eosinophilic to clear cytoplasm. The cells expressed the germ cell markers (i.e. PLAP, Oct4 and SALLA4) with a small number of T lymphocytes present. Only a minimal number of optic nerve fibers remained at the periphery of the nerve (as outlined on the pathology slides by NF & LFB/PAS stains).