Objective: To describe a rare diagnostic pitfall on F-18 FDG PET/CT caused by FDG-avid non-ossifying fibromas (NOFs) in a pediatric patient with Ewing sarcoma.

Case: We retrospectively evaluated PET/CT findings in a 15-year-old male diagnosed with histologically confirmed Ewing sarcoma of the thoracic wall. Whole-body F-18 FDG PET/CT was performed for initial staging. Lesions with abnormal uptake were further evaluated using radiologic imaging to assess morphology and confirm the benign nature of incidental findings.

Results: PET/CT showed no evidence of distant metastasis. However, two focal FDG-avid bone lesions were identified incidentally: one in the distal right femur (SUVmax: 19.9) and another in the proximal left tibia (SUVmax: 6.8). Both demonstrated higher FDG uptake than the primary tumor (SUVmax: 6.7). Radiographs and MRI revealed well-circumscribed, cortically based lesions with imaging features typical of non-ossifying fibromas, confirming their benign nature.

Conclusion: FDG-avid NOFs may mimic skeletal metastases on PET/CT, potentially leading to misinterpretation and unnecessary interventions. Correlation with conventional imaging such as MRI and radiographs is crucial to avoid overstaging and guide appropriate clinical management in pediatric oncology.