Chondrosarcoma and Its Precursors

The most common primary malignant tumors of bone after osteosarcoma is chondrosarcoma (1;2). The highest incidence is in the fourth decade of life (2). In addition to bone sarcomas several benign bone neoplasms are known, from some of which little etiology and epidemiological information is available, because many of them are asymptomatic and therefore diagnosed only incidentally. Benign bone tumors are more frequent than bone sarcomas and may in case of cartilaginous tumors act as precursor of their malignant counterpart. The preoperative assessment of cartilaginous lesions is based upon careful radiological documentation, clinical presentation and histopathologic evaluation of a biopsy specimen (3;4). In general practice, the primary differential diagnosis will be made based upon radiology and clinico-demographic data (2). Usually plain radiographs provide substantial information. Within the diagnostic field of cartilaginous tumours additional progress has been made using (dynamic) MRI, especially for the distinction between benign and low-grade malignant cartilaginous lesions. Regarding the differential diagnosis of osteochondroma versus low-grade peripheral chondrosarcoma the thickness and staining characteristics on (dynamic) MR of the cartilaginous cap provide a rather reliable assessment of the likelihood of malignancy (5). For the distinction between enchondroma and central grade I chondrosarcoma, clinical symptoms and radiographic features are of help, but both lack specificity {Sanerkin, 1980 3587 /id;Schiller, 1985 3588 /id;Geirnaerdt, 1997 4214 /id;}. Localisation in the axial skeleton and size greater than 5 cm have been shown to be a reliable predictor for malignancy (6). Previous studies demonstrate that conventional radiography is not reliable in this differential diagnosis, amongst others hampered by the absence of objective and reproducible criteria (6). Recent studies however using dynamic contrast enhanced MR-imaging show increased sensitivity (5;7;8). However, even by means of dynamic contrast enhanced MR-imaging evaluated by an experienced bone tumor radiologist, an absolute distinction between malignant and benign can not be made on radiological grounds alone (9;10). Therefore, when the radiological assessment of a benign versus a lowgrade malignant central cartilaginous tumor remains in doubt, a biopsy has to be taken and assessed by an experienced pathologist, who evaluates the biopsy using all available radiological information and applying defined histopathologic criteria.