Pitfalls in the MR diagnosis of primary malignant bone tumors

MRI has gained an undisputed place in the evaluation of malignant bone tumors, not only for verifying results of conventional radiographs and clarifying differential diagnoses; it has also become increasingly important for the assessment of the malignant/benign nature of the tumor, its growth rate, definition of adequate sites for biopsy, local preoperative staging, and evaluation of the response to chemotherapy. However, several pitfalls have to be observed regarding choice of technical parameters (coils, sequences, imaging planes), tissue differentiation, and tumor staging. When staging malignant tumors, critical aspects which have to be observed are tumor extension, integrity of the cortical bone, soft tissue components, infiltration of a joint or neurovascular bundle. The use of contrast agents provides important additional information but can also give rise to misinterpretations. Thus, all features of a tumor have to be observed in order to establish a final diagnosis. Particular difficulties can occur with the interpretation of MR images of osteomyelitis, osteoid osteoma, stress and insufficiency fractures, bone infarcts, myositis ossificans, hemangiomas, and aneurysmal bone cysts.