MR CRITERIA FOR DIFFERENTIATION OF PSEUDO TUMOUROUS LESIONS FROM BONESARCOMAS OF THE EXTREMITIES

The MRT scans of 57 patients with Ewing or osteosarcomas and 34 patien ts with haematogenous osteomyelitis or periostitis/stress fractures we re examined in order to determine whether a distinction between benign or malignant lesions is possible. Four criteria were evaluated: the m argin of the bone marrow component; intensity and homogeneity of the T 1 weighted signal in the bone marrow; presence of an extraosseus struc tured soft tissue mass and/or soft tissue edema. It was found that cen tral osteosarcomas and Ewing's sarcomas reduced signal intensity of th e marrow to become muscle-isointense with a well defined margin. In ac ute haematogenous osteomyelitis and periostitis/stress fracture the ma rrow lesion was not sharply demarcated. In contrast to patients with b one sarcomas, only one case of osteomyelitis showed an extrosseus stru ctured soft tissue mass. On the basis of these findings we believe tha t acute haematogenous osteomyelitis can be distinguished with high deg ree of accuracy from Ewing's sarcoma and central osteosarcomas.