Concurrent Polyostotic Fibrous Dysplasia and Osteosarcoma: A Diagnostic Dilemma in the Era of FDG PET/CT Imaging

Fibrous dysplasia (FD) is a benign bone condition characterized by increased fluorodeoxyglucose (FDG) uptake on positron emission tomography/ computed tomography imaging, which can occasionally mimic cancer. The unusual change of FD to secondary osteosarcoma poses a severe diagnostic challenge, especially when imaging reveals nonspecific metabolic activity, necessitating histological confirmation. This case-based study underlines the challenges of distinguishing FD from osteosarcoma, particularly in individuals with polyostotic involvement, and underscores the importance of integrated radiologic–pathologic correlation. We provide a case of a patient with concurrent FD and osteosarcoma in both lower limbs, with one leg showing FDG avidity in polyostotic FD and the left limb pathologically diagnosed as osteosarcoma with distinctive radiographic appearance.