Magnetic resonance imaging in malignant bone tumours. 
Complete removal of the tumour without leaving microscopic disease is vital in the management of bone sarcomas.  Magnetic resonance imaging now seems to be the best method of depicting the changes produced by the tumour within the bone and surrounding soft tissues.  In order to define its reliability, five cases of primary bone sarcomas (Ewing's sarcoma, osteosarcoma, chondrosarcoma) are described where radiographs, bone scans and magnetic resonance images are directly compared to the pathological findings after resection.  We conclude that surgical margins should be redefined with respect to the extent and borders of the tumour as depicted by magnetic resonance imaging.  This will allow improvement in salvage procedures, but further experience is needed so as not to jeopardize the prognosis by incomplete removal of the tumour.