Abstract
INTRODUCTION: WHO classification of brain tumor was revised in 2016, with removal of primitive neuroectodermal tumor (PNET) from its classification entity. Thus, tumor previously diagnosed as PNET should be reclassified. In this report, we present a case, in which molecular diagnosis was useful to accurately classify the tumor that was previously diagnosed as PNET to spinal cord Ewing sarcoma. CASE REPORT: 50-year-old woman presented 3 months history of motor / sensory disturbance of both lower -extremities and lower back pain, as well as one week history of walking difficultly. Magnetic resonance imaging (MRI) of the spinal cord showed an intradural tumor that extended from the Th11-12 to cauda equina. She underwent subtotal removal of the tumor. Then postoperatively, she received 39.6 Gy of whole craniospinal irradiation, followed by 14.4 Gy of local irradiation, in combination with chemotherapy (Carboplatin + VP-16). The tumor showed partial response to the chemoradiotherapy. PATHOLOGICAL FINDINGS: Histopathologic examination revealed malignant small round-cells with hyperchromatic nuclei that were immunoreactive for CD99, synaptophysin and NeuN. Thus, at first the tumor was diagnosed as PNET. However, further molecular investigation revealed EWS(exon7)-FLI1(exon6) fusion gene, that changed the diagnosis of this tumor to Ewing sarcoma. DISCUSSION: Intramedullary Ewing’s sarcoma is extremely rare. Molecular diagnosis was useful to classify spinal cord Ewing sarcoma. The patient was treated following our protocol that had been used for adult medulloblastoma and a good therapeutic response has been obtained.