Figure 3b. (a) Anteroposterior radiograph of the left hip in a 31-year-old woman. A highly permeative lesion is seen to involve the superior acetabulum and extend to the ischium and superior pubic ramus. (b, c) T2-weighted MR images (2,700/104) obtained at the level of the ischium (b) and at the junction of the proximal and middle thirds of the thigh (c) demonstrate a high-signal-intensity soft-tissue mass that infiltrates surrounding muscle and extends far beyond the osseous involvement; multiple muscle compartments are involved. The long proximal and distal extent, coupled with the involvement of multiple compartments and invasiveness, distinguish this lesion from the round and more focal masses usually seen in osseous sarcomas, and suggest the diagnosis of primary lymphoma of bone.