After localizing a lesion, the imaging charac­teristics of a tumor need to be evaluated. A mass involving bone or adjacent to bone may have an internal bony matrix identiable on CT scan or plain lms. If the matrix is calcied, it may offer a clue to the histology of the underlying mass. For example, cartilaginous neoplasms can have ringlike or arc-like calcications. In addition the bony edge or margin of a lesion should be exam­ined. A sharp, well-dened edge usually indi­cates a slow-growing process. Irregular, poorly dened margins often indicate an aggressive process. Finally some tumors (such as giant cell tumor, osteoblastoma, and aneurysmal bone cyst) can expand the bones they involve, and this can be detected with CT scan and plain radiographs [26]. CT scan evaluation of soft tissues can be augmented with intravenous contrast material. In patients with suspected malignant spinal cord compression (MSCC), subarachnoid (intrathe­cal or myelographic) contrast can help detect the level of spinal cord compromise due to epidural mass effect from metastatic disease. CT myelog­raphy also helps discern intramedullary tumors from intradural-extramedullary tumors.