A and B, Anteroposterior and lateral radiographs of proximal femur of 67-year-old woman with periosteal osteosarcoma. C, MR image shows lesion arising from surface of bone. Marrow does not seem to be involved. D, Specimen after wide resection. E, Specimen after removal of surrounding muscle. F, Cut specimen. Lesion arises from surface of bone, and marrow cavity is not involved. G, Typical microscopic appearance of periosteal osteosarcoma. Lobules of malignant cartilage are separated by malignant spindle cells producing osteoid. H, Anteroposterior radiograph of reconstructed femur.