[The MRT criteria for the differentiation of "pseudotumorous" lesions from bone sarcomas of the extremities].

The MRT scans of 57 patients with Ewing or osteosarcomas and 34 patients with haematogenous osteomyelitis or periostitis/stress fractures were examined in order to determine whether a distinction between benign or malignant lesions is possible. Four criteria were evaluated: the margin of the bone marrow component; intensity and homogeneity of the T1 weighted signal in the bone marrow; presence of an extraosseous structured soft tissue mass and/or soft tissue edema. It was found that central osteosarcomas and Ewing's sarcomas reduced signal intensity of the marrow to become muscle-isointense with a well-defined margin. In acute haematogenous osteomyelitis and periostitis/stress fracture the marrow lesion was not sharply demarcated. In contrast to patients with bone sarcomas, only one case of osteomyelitis showed an extraosseous structured soft tissue mass. On the basis of these findings we believe that acute haematogenous osteomyelitis can be distinguished with high degree of accuracy from Ewing's sarcoma and central osteosarcomas.