MALIGNANT-TUMORS OF THE OSTEOGENIC MATRIX

This article focuses on major clinical and imaging features that are o f practical interest in the diagnosis and management of osteosarcoma, a malignant tumor arising from the osteogenic matrix. The current hist ologic classification of this tumor is also reported. Different types of osteosarcoma are described, each of them with a definite clinical a nd radiographic pattern. Conventional radiography is the keystone to d iagnosis because it allows analysis of the patterns relevant to the di fferent 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 osteoscle rotic or osteolytic, but more frequently it has a mixed (osteoslerotic /osteolytic) pattern. The teleangiectatic osteosarcoma is an aggressiv e form (5%) characterized by marked vascularization with large blood-f illed cystic cavities; its typical radiographic pattern is purely oste olytic. Juxtacortical osteosarcoma (8-10%) indicates a group of osteos arcomas apparently arising on bone surface. The most common type is pa rosteal osteosarcoma which affects older subjects and has a better pro gnosis than the classic type. Radiography shows a heavily ossified mas s with a broad base attached to the underlying cortex. CT and MRI are useful in the differential diagnosis of osteosarcoma and myositis ossi ficans or osteocondroma. Rare types of osteosarcoma include the perios teal and high-grade surface variants, as well as secondary and multifo cal osteosarcoma (osteosarcomatosis). CT and MRI are the imaging proce dures 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 m ore useful when paramagnetic contrast agents are administered because dynamic MRI with contrast enhancement help differentiate postchemother apy changes from viable tumor-the latter enhancing rapidly and the for mer slowly. Thus, dynamic MRI allows a precise mapping of any residual tumor activity. (C) 1998 Elsevier Science Ireland Ltd. All rights res erved.