Biopsy reveals Intermediate to high grade osteosarcoma with prominent cartilaginous component.

Periosteal osteosarcoma arises from the inner layer of periosteum (parosteal osteosarcoma arises from outer layer) and contain large amount of cartilaginous matrix.

Periosteal osteosarcoma are worse than parosteal osteosarcoma but better than conventional osteosarcoma in terms of prognosis.