Parosteal Osteosarcoma Wheeless

Description: Discussion: - parosteal osteosarcoma is a low-grade malignant bone tumor that usually occurs on the surface of the metaphysis of long bones; - arises between cortex and muscle as a low grade stage I-A surface tumor (ie does not initially invade underlying medullary canal); - most common in adolescents and yound adults; - parosteal osteosarcoma is distinguished from classic osteosarcoma by its much slower, less aggressive clinical course. - there is a low propensity to metastasize; - about 10% of parosteal tumors exhibit areas of dedifferentiation into high grade sarcoma & are thus considered stage IIb lesions. - tumor remains separated from normal bone, especially in the early stage; - extension into the underlying bone is associated with a higher incidence of dedifferentiation and pulmonary metastasis; - as growth continues, radiolucent zone between tumor & underlying bone may be obliterated as cortex becomes involved; - late in dz, tumor extends through the underlying cortex to invade medullary canal as well, converting to a stage Ib tumor; - invasion into the overlying displaced soft tissues is rare