Abstract
INTRODUCTION: Fibrous dysplasia is tumor like lesions of bone which develop as substitution of bone by an expansion of fibrous connective tissue mixed with hard trabeculae. Chondrosarcomas is one of common malignant primary bone tumor derived from heterogenous group of neoplasm producing chondroid matrix. Chondrosarcoma arising in fibrous dysplasia, especially in monostotic fibrous dysplasia is a very rare case. CASE REPORT: A 54-year-old male presented with chief complaint of pain on left thigh. Patient with history of pathological fracture on left femoral diaphysis 3 years ago due to fibrous dysplasia and had underwent curettage, open reduction, and internal fixation at other hospital. Plain radiography revealed expansive lytic lesion, interrupted periosteal reaction with plate and screw attached to the lesion, and soft tissue mass. MRI T2FS sequence showed hyperintense mass extending from subtrochanteric to distal of left femoral diaphysis. Histopathological result from biopsy suggested chondrosarcoma. CONCLUSIONS: Malignant transformation of monostotic type was less frequently compared to polyostotic type. Among all malignant transformation cases, alteration to chondrosarcoma was more scarce than other malignancy such as osteosarcoma and fibrosarcoma. Wide surgical margin and reconstruction in chondrosarcoma provide good local control and functional outcome.