Osteosarcoma with Emphasis on Surface Osteosarcoma

A review was performed of 42 cases of pathologically-proved osteosarcoma from January 1980 to April 1994. The term ”surface osteosarcoma” indicated an osteosarcoma arising on the periosteal aspect, namely either parosteal osteosarcoma, periosteal osteosarcoma and high-grade surface osteosarcoma. This subgroup of osteosarcoma differs from conventional osteosarcoma both clinicopathologically and radiolographically. There were two cases of parosteal osteosarcoma (5%), and three cases of periosteal osteosarcoma (7%) in the series here in comparison to 4-5% parosteal osteosarcoma and 2% periosteal osteosarcoma of all primary osteosarcomas in the others' series. Typically a parosteal osteosarcoma is Grade I malignant neoplasm, and has a much better prognosis than conventional osteosarcoma. The mean survival in our two parosteal osteosarcoma cases was more than ten years in contrast to 10.3 months in conventional osteosarcoma in our study. The criteria for diagnosis of periosteal osteosarcoma were based on the location of the tumor on the diaphysis plus a histologically Grade II-III malignancy with predominant malignant cartilage, with or without marrow involvement. The mean survival time of 11.6 months in the three periosteal osteosarcoma cases was slightly better than that in conventional osteosarcoma, presumably because of its relatively well- differentiated chondroblastic and less aggressive features. Three of the 42 cases (7%), aged 9,14 and 16 years respectively, had a dominant high-grade intramedullary osteosarcoma with subsequent multiple pulmonary and skeletal lesions within five months, compatible with the so-called ”metastatic osteosarcomatosis”. Malignant transformation of osteoblastoma as it occurred in three patients in this series was controversial because of some histologic similarity between osteoblastoma and low- grade osteosarcoma.