The meaning of radiolucencies in parosteal osteosarcoma.

Parosteal osteosarcoma with either intralesional radiolucencies or extralesional clefts within the tumor was identified in eighteen patients. In each patient, both high-quality radiographs and whole macrosections of the lesions were available for correlative study of the radiolucencies. The intralesional radiolucencies were characterized as either deep or peripheral. Study of the macrosections showed that most of the peripheral lucent areas were comprised of low-grade malignant cartilaginous or fibrous tissue that was mixed with fat and bone trabeculae. The majority (67 per cent) of the high-grade dedifferentiated areas of tumor, however, corresponded to the deep radiolucencies. We think that the presence of a deep radiolucent area on a computed tomographic scan or other preoperative radiographic staging studies must create suspicion that a high-grade (grade-II) dedifferentiated region exists within an otherwise low-grade parosteal osteosarcoma.