Primary Extraosseous Central Nervous System Ewing Sarcoma in Children: A Rare Case Series from a Major Public Neuro-Oncology Center in Pakistan.

Primary extraosseous central nervous system Ewing Sarcoma (CNS-EES) in children is a rare disorder, and this study aimed to document the experience of dealing with these rare pathologies of CNS in our center. This ambidirectional descriptive case series included all consecutive cases of CNS-EES in children under the age of 16 years presenting to the The Children's Hospital Lahore, Pakistan, from January 2023 to December 2024. During the 24-month study period, 4 out of 139 incident CNS tumor cases at our center were diagnosed as primary CNS-EES, corresponding to a proportional incidence of 2.9% (95% CI: 1.1-7.2%). The median age of presentation was 8.5 years, with equal gender distribution. Pain was the first presenting symptom, with a median symptom duration of 5.75 weeks. Half of the cases presented with a cerebral hemispheric mass and half with a spinal mass. The median event-free survival was 4.5 weeks with a survival rate of 25%. All cases were diagnosed based on a round blue cell morphology with a positive NKX2.2. Primary CNS-EES is not very infrequent in our population, with possible parietal lobe predilection and association with cancer predisposition syndrome. In resource-limited settings, NKX2.2 might serve as a fair substitute to diagnose CNS-EES.