Ewing's sarcoma: imaging features.

Location in the pelvis was most frequent (31%), followed by the femur (20%) and tibia (11%). Most tumors were mixed lytic-sclerotic (75%), and purely lytic in 25%. Plain films and CT scan showed a spiculated periosteal reaction in 50%. A Codman's triangle was seen in 27%. Articular extension was difficult to assess on radiographs. Cortical permeation and destruction is seen in respectively 31 and 42%, whereas cortical thickening is seen in 20%. Pathologic fracture occurred in 7.8%. MRI showed a large mass, with a soft tissue component of more than 50% in 67%. Degree and pattern of enhancement pattern was variable. Signal intensity on T1- and T2-WI was non-specific. Joint involvement was seen in 23%. Isolated involvement of the soft tissue (extraskeletal ES) was seen in 1.5%. Skip metastases at initial presentation were present at initial presentation in 14% and distant metastases in 22%. Conclusions: ES occurs in young patients. On radiographs/CT, 37.5% are located in the axial skeleton and 62.5% in the peripheral skeleton. ES is mostly mixed sclerotic-lytic. A spiculated periosteal reaction is most frequent.The most characteristic finding on MRI is the presence of a large soft tissue mass.