Periosteal Chondrosarcoma

Periosteal chondrosarcoma is a rare surface, or juxtacortical, malignant cartilage tumour that arises on the bone surface, typically at the metaphysis of a long bone such as the femur, and the great majority are low or intermediate grade with indolent behaviour and a good prognosis. So my approach is to characterise and grade it properly before treating. On imaging it shows a chondroid matrix with cortical scalloping or buttressing and a surface soft-tissue mass; I would use radiographs and CT for the matrix and cortex and MRI for extent. I would distinguish it from the two main alternatives: the benign periosteal chondroma, which is small, usually a few centimetres; and surface osteosarcoma, which produces osteoid rather than a chondroid matrix. A benign-looking surface chondroma that is large or aggressive should make me suspect chondrosarcoma. I would obtain a properly planned biopsy read at a specialist sarcoma centre to confirm the diagnosis and grade, and a proportion of these tumours carry IDH1 mutations which can support the diagnosis. Management of the usual low-grade lesion is adequate surgical excision - marginal excision suffices for low-grade disease, with wider margins for the uncommon higher-grade tumours - and because cartilage tumours are relatively resistant to chemotherapy and radiotherapy, surgery is the mainstay. The prognosis is good, with recurrence and metastasis uncommon and largely confined to the few high-grade or dedifferentiated lesions. As always, I would avoid an unplanned excision of an undiagnosed surface mass.