Low grade central osteosarcoma-a diagnostic challenge

Low Grade Central Osteosarcoma (LGCO) is a rare intramedullary and well differentiated variant of osteosarcoma with a better prognosis than the more common conventional variant. It was first described by Unni et al., in 1977. Due to its subtle histological features of malignancy, it is difficult to diagnose on biopsy. Even in the resection specimen it can be mistaken for lesions like fibrous dysplasia, desmoplastic fibroma, parosteal osteosarcoma and fibrosarcoma. Adequate sampling of the tumour is essential to arrive at a correct diagnosis. Histological features such as cytological atypia, mitotic activity, permeation into the bone marrow, entrapment of the native bone, cortical disruption and soft tissue extension will help in the diagnosis of this tumour. We report a case of a 30-year-old man who presented with pain in the right hip of three months duration. On radiological evaluation, a lytic lesion was noted in the upper part of right femur and a possible diagnosis of locally aggressive giant cell tumour of bone was proposed. On histopathological study of the resected upper part of the right femur, a diagnosis of LGCO was rendered.