Microscopic correlation of radiographically disparate appearing well differentiated osteosarcoma

Well differentiated (low grade) osteosarcomas are often unrecognized and inadequately treated. We report on a patient with a well differentiated osteosarcoma of the tibia that radiographically presented with two strikingly dissimilar appearing juxtaposed lesions. Proximally, the lesion was sclerotic, and distally, osteolytic. The distal lytic half of the lesion showed focal cortical disruption on MR imaging. Microscopic correlation of the resected specimen suggested that the sclerotic component of the lesion had more fibrous dysplasia-like tissue with fewer features of well differentiated osteosarcoma, and the lytic component, features suggestive of well differentiated osteosarcoma. We believe this microscopic interpretation explains the disparate radiographic appearance as all belonging to well differentiated osteosarcoma with varying amounts of fibrous dysplasia-like tissue rather than the development of well differentiated osteosarcoma in fibrous dysplasia.