Etmr-16. Pediatric Spinal Embryonal Tumors; Pathological Insights Into This Rare Entity

Abstract BACKGROUND Spinal cord is an extremely uncommon primary location for the CNS embryonal group of tumours. This study aims to collate the immunohistological spectrum of these rare spinal CNS embryonal tumours, diagnosed in the institute during the last 20 years. METHODS Of the total 446 spinal tumours, 15 were embryonal tumours. Of these, 5 were metastases, four from medulloblastoma and one from AT/RT (diagnosed subsequently) which were excluded and thus the study cohort comprised 10 cases. Eight were atypical teratoid/rhabdoid tumour (AT/RT; 80%), and 2 were embryonal tumour with multilayered rosettes (ETMR; 20%). RESULTS Six AT/RT cases were of ≤2 years age; while other two were 6 and 11 years of age with a M:F ratio of 1.3:1 (thoracic: 4; cervical: 2; lumbar: 2). Histologically, rhabdoid-like morphology (87.5%), necrosis (100%), and calcification (25%) were noted. All of them were of INI1 protein (SMARCB1)-deficient., all of them were negative for brachyury and all were variably positive for AE1/AE3. Two ETMR cases were of 2 years of age, females and at lumbar and cervical levels respectively. C19MC amplification by FISH was done for one case which was not amplified. Histologically, one of them showed a medulloepithelioma-like pattern; while the other showed multilayered rosettes and neuropil-like matrix. LIN28A strong positivity, retained nuclear staining for INI1 protein and negativity for AE1/AE3 was noted in both. Significant BCOR positivity was seen in one but was negative for SATB2. CONCLUSIONS Spinal embryonal tumours are extremely rare and metastases needs to be ruled out before considering as primary. AT/RT is the most common embryonal tumour in the spine, commonly SMARCB1(INI1)-deficient. ETMR can also encountered in the spinal location.