Incidental Bone Scan Appearance of a Pleural Metastasis in Parosteal Osteosarcoma

A 25-year-old woman presented with a known case of low-grade parosteal osteosarcoma of the right leg and underwent distal femur replacement. Preoperative workup was negative for distant metastases. Two years later, regular oncologic surveillance including CT was unremarkable. Two and a half years later, the patient developed symptoms of prosthetic material loosening. Tc-99m methylene diphosphonate whole-body bone scanning and SPECT/CT did not show evidence of loosening, but revealed a pleural sarcoma metastasis, which was confirmed by histopathology. Tc-99m methylene diphosphonate uptake has been observed in the soft tissue and lungs in patients with osteosarcoma, but is rarely observed in clinical practice.