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.