Abstract

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.

Key words: F-18 FDG PET/CT, non-ossifying fibroma, pediatric oncology, benign bone tumor, Ewing sarcoma