GCT-06. DIAGNOSIS OF A RARE CASE OF RECURRENT GERM CELL TUMOR BY CSF PLACENTAL ALKALINE PHOSPHATASE PRESENTING WITH DIFFUSE INTRAAXIAL ABNORMALITY IN THE LOWER BRAINSTEM

INTRODUCTION: Germ cell tumors in the central nervous system (CNS) typically arise either at suprasellar and/or pineal region, and occasionally at basal ganglia. We report a case of diagnostically challenging, recurrent germ cell tumor presented with diffuse intraaxial abnormality in and across the lower brainstem, which was diagnosed by the elevated placental alkaline phosphatase (PLAP) level in cerebrospinal fluid (CSF). CASE DESCRIPTION: A 28-year-old man had been treated by chemoradiotherapy at the previous hospital for bifocal suprasellar and pineal lesions with the provisional diagnosis of germinoma without histological confirmation. Three years later, he presented with progressive weakness of bilateral extremities for weeks. Magnetic resonance imaging showed a diffuse, bilaterally symmetric high intensity lesion on T2-weighted image with slight contrast enhancement across the ventral side of the medulla oblongata to the upper cervical spinal cord. Serum and CSF hCG, hCG-β, and AFP were all negative. Since the image findings were atypical for recurrent germ cell tumor, some kind of myelitis was initially suspected. Therefore, steroid pulse therapy was administered. However, the patient’s symptom was still gradually progressing. Then, the CSF PLAP turned out to be positive, indicating the recurrence of germinoma. Accordingly, platinum-based chemotherapy was administered, and the imaging findings, patient’s symptoms, and CSF PLAP began to improve. The patient is to be treated with radiotherapy following chemotherapy. CONCLUSION: We report a rare case of CNS germ cell tumor that presented with diffuse intraaxial lesion in the lower brainstem in which examination of CSF PLAP was extremely useful.