Periosteal osteosarcoma is a form of surface osteosarcoma.
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Epidemiology
It is the second most common type of juxtacortical or surface osteosarcoma after parosteal osteosarcoma and accounts for 1.5% of all osteosarcoma cases. It affects a slightly older age group (10-20 years) cf. conventional osteosarcoma.
Diagnosis
The diagnosis of periosteal osteosarcomas is based on a combination of typical radiographic features and histology.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of bone tumors (2020 - blue book) 1:
imaging features of a bone tumor
histology of an intermediate-grade mostly chondroblastic osteosarcoma
origin from the surface of the bone under the periosteum
Pathology
Periosteal osteosarcomas arise from the inner germinative layer of the periosteum. The cytologic grade of this tumor is higher than parosteal osteosarcoma and lower than conventional osteosarcomas, so it is considered as intermediate grade osteosarcoma (grade 2). It predominantly contains a chondroid matrix.
Location
lesions tend to be diaphyseal
femur and tibia most common, especially medial distal femur
arises from the cortex, being attached to the underlying cortex at origin; intramedullary extension is rare
Radiographic features
Typically seen as a broad-based surface soft-tissue mass causing extrinsic erosion of thickened underlying diaphyseal cortex and perpendicular periosteal reaction extending into the soft-tissue component:
predominantly chondroid matrix results in a lesion that is low in attenuation on CT images and hyperintense on T2 weighted MR images and tend to “wrap around” the circumference of the bone
a periosteal reaction common, as sunburst pattern (radiating from the bone surface) or a Codman triangle
MRI
typically hypointense on both T1 and T2 sequences: may see bony spicules radiating from the surface lesion (sunburst pattern)
it may appear hyperintense on the T2 sequence which represents its chondroid matrix.
reactive marrow changes are commonly seen at MR imaging, but true marrow invasion is rare 2
it is difficult to differentiate periosteal osteosarcoma from the conventional high-grade osteosarcoma at imaging, however, conventional osteosarcomas involve the entire circumference of the cortex and show intramedullary extension.
Treatment and prognosis
Periosteal osteosarcoma is of intermediate grade with the prognosis being better than conventional osteosarcoma, but not as good as parosteal osteosarcoma (which is usually low grade).
