Paediatric Primary Renal Ewing Sarcoma – Staging and Response Assessment Using Fluorodeoxyglucose Positron Emission Tomography

Primary renal Ewing sarcoma is an extremely rare malignant neoplasm in children. We present the case of a 3-year-old boy, incidentally, detected with a right renal mass diagnosed as an Ewing sarcoma. Baseline 18 F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET- CT) revealed a large heterogeneous hypermetabolic mass. Biopsy confirmed Ewing sarcoma/Ewing sarcoma spectrum with CD99 and NK2 homeobox 2 (NKX2-2) positivity and absence of EWS RNA-binding protein 1 (EWSR1)1 rearrangement. Following neoadjuvant VDC (vincristine, doxorubicin, cyclophosphamide) /IE (Ifosfamide, Etoposide) chemotherapy, response assessment 18 F-FDG PET-CT demonstrated a complete metabolic response. The child subsequently underwent definitive surgery, and histopathology revealed a complete pathological response (ypT0N0). This case highlights the role of 18 F-FDG PET-CT in staging, treatment response assessment and surgical planning in this rare paediatric tumour.