Malignant tumors of the osteogenic matrix.

This article focuses on major clinical and imaging features that are of practical interest in the diagnosis and management of osteosarcoma, a malignant tumor arising from the osteogenic matrix. The current histologic classification of this tumor is also reported. Different types of osteosarcoma are described, each of them with a definite clinical and radiographic pattern. Conventional radiography is the keystone to diagnosis because it allows analysis of the patterns relevant to the different lesions (location, site, bone destruction, periostal reaction, soft tissue masses). The most common type of osteosarcoma is defined classic or conventional high grade (75%) and it typically involves the medullary cavity. Radiographically, it may be predominantly osteosclerotic or osteolytic, but more frequently it has a mixed (osteoslerotic/osteolytic) pattern. The teleangiectatic osteosarcoma is an aggressive form (5%) characterized by marked vascularization with large blood-filled cystic cavities; its typical radiographic pattern is purely osteolytic. Juxtacortical osteosarcoma (8-10%) indicates a group of osteosarcomas apparently arising on bone surface. The most common type is parosteal osteosarcoma which affects older subjects and has a better prognosis than the classic type. Radiography shows a heavily ossified mass with a broad base attached to the underlying cortex. CT and MRI are useful in the differential diagnosis of osteosarcoma and myositis ossificans or osteocondroma. Rare types of osteosarcoma include the periosteal and high-grade surface variants, as well as secondary and multifocal osteosarcoma (osteosarcomatosis). CT and MRI are the imaging procedures of choice in locoregional staging (intraosseous and extraosseous spread, skip metastases, growth plate and articular involvement). CT of the chest is a useful tool for detecting lung metastases. Also MRI has a role in monitoring the response to chemotherapy and in detecting recurrence. It permits a more accurate study of the tumor volume than other imaging techniques and clinical examination. MRI becomes even more useful when paramagnetic contrast agents are administered because dynamic MRI with contrast enhancement help differentiate postchemotherapy changes from viable tumor--the latter enhancing rapidly and the former slowly. Thus, dynamic MRI allows a precise mapping of any residual tumor activity.