Periosteal osteosarcoma is a relatively rare subtype. It is classified as a distinct category due to its unique anatomical and histological characteristics, and also because its prognosis is better than that of central osteosarcoma.

bubble_chart Pathological Changes

The histological features of periosteal osteosarcoma are similar to those of peripheral osteosarcoma, often with better differentiation and rarely showing a myxoid appearance. In periosteal osteosarcoma, if the histological features are identical to grade I osteosarcoma, it is highly likely to be a benign tumor, possibly a periosteal osteochondroma. The histological manifestations of grade II-III periosteal osteosarcoma are the same as those of grade II-III peripheral osteosarcoma, and grade III periosteal osteosarcoma is also rare. Periosteal osteosarcoma can also undergo malignant progression.

bubble_chart Clinical Manifestations

The gender and age distribution is similar to conventional osteosarcoma. It is located in the metaphysis or one end of the diaphysis of long bones, commonly occurring in the femur, tibia, and humerus, and rarely in short or flat bones.

The main symptom is swelling, accompanied by grade I pain or no pain.

bubble_chart Auxiliary Examination

X-ray findings show a spherical mass, sometimes with an irregular surface, located on the surface of the cortical bone, which may originate from the periosteum or outside the periosteum. Similar to parosteal osteosarcoma, when periosteal chondrosarcoma is located in the distal femur, it is often situated posteriorly and extends into the popliteal fossa. Periosteal chondrosarcoma presents as a cartilaginous mass, sometimes not visible on X-ray films, and its boundaries can only be delineated through CT or MRI examinations. The tumor often contains granular, punctate, and ring-like calcifications, occasionally with indistinct linear ossifications. The underlying cortical bone may sometimes be intact, while at other times its surface is eroded. The erosion of the cortical bone can be indistinct but often appears as a well-defined, thick, saucer-shaped indentation. There may be a periosteal reaction around the tumor, producing triangular ossifications that partially encircle the base of the tumor.

Under the same histological conditions, parosteal osteosarcoma has a lower malignancy than central osteosarcoma. It can be cured by wide resection and is often treated with limb-sparing therapy, with rare or no metastasis.

bubble_chart Differentiation

It is necessary to differentiate from periosteal chondrosarcoma. On imaging, periosteal osteosarcoma is more expansive, erodes cortical bone, and does not invade the medullary cavity. However, the most important differentiation is histological. It should be noted that grade I atypia in periosteal bone tumors represents benign lesions, not malignant ones, especially in childhood. Therefore, the diagnosis of grade I periosteal osteosarcoma may be incorrect. Periosteal osteosarcoma also needs to be differentiated from parosteal osteosarcoma. Parosteal osteosarcoma invades the diaphysis and appears on imaging as X-ray-opaque spicules perpendicular to the cortical bone. Histologically, despite abundant chondroblasts, tumorous osteogenesis can be observed.