High grade periosteal osteosarcoma (also known as high grade surface osteosarcoma) accounts for less than 1% of all osteosarcoma.  The only difference between conventional osteosarcoma and high-grade per osteal osteosarcoma is the location of the latter on the surface of the bone.
     High grade periosteal osteosarcoma appears malignant on plain x-ray. There is irregular cortical destruction as well as irregular periosteal reaction. Bone marrow infiltration is visible on MRI.
     High grade periosteal osteosarcoma appears identical to conventional osteosarcoma microscopically. The tumors are treated similarly and have the same prognosis.

References
Bloem, JL and HM Kroon, Osseous Lesions, Radiologic Clinics of North America, 31(2):261-277, March 1993.

Bullough, Peter, Orthopaedic Pathology (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991.

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