(A1108) Clinical Presentation of Malignant Transformation from Fibrous Dysplasia to Osteosarcoma: A Case Report

Introduction: Fibrous dysplasia (FD) is a benign bone disorder characterized by the replacement of normal bone with abnormal fibrous tissue. While generally considered a benign condition, FD has been associated with rare instances of malignant transformation, most commonly to osteosarcoma. The infrequency of this transformation makes it a diagnostic challenge, highlighting the importance of vigilant monitoring.

Methods: A 37-year-old female with a long-standing history of right craniofacial FD presented to our clinic with facial pain and hearing loss. At 20-years-old, she had undergone her first partial tumor excision followed by several craniofacial reconstructive surgeries, with goals of tumor reduction and cosmesis. After being lost to follow up for nearly 10 years, the patient re-presented with worsening left facial pain.

Results: Interval imaging demonstrated progressive, contrast enhancing T1 and T2 intermediate tumor involving the left pterygopalatine fossa as well as multiple pulmonary nodules, suggesting potential malignant degeneration and metastatic disease. Histopathology from endoscopic endonasal debulking biopsy and PET scans confirmed dedifferentiated (high-grade) osteosarcoma and lung and bone metastases, respectively.

Conclusions: We aim to present this rare case to spread awareness about the notable potential for malignant transformation from FD to osteosarcoma. Lifelong follow-up with attention to specific changes in symptoms – such as new onset pain, numbness, tinnitus, vision changes – and radiologic findings is critical.