Ewing's sarcoma: imaging features

To define an imaging prototype of Ewing's sarcoma (ES).

Sixty-four patients with a histopathologically and/or genetically proven diagnosis of ES were analyzed for clinical parameters (age, gender and location), radiographic and CT appearance (distribution, matrix, margins, periosteal reaction, articular extension, cortical reaction and the presence of a pathologic fracture). Size, local extension, signal intensity, degree and pattern of enhancement, and the presence of skip metastases were evaluated on MRI. Distant metastases were recorded on bone scintigraphy and chest CT scan.

Patient's age ranged between 7-67 (mean 17.9). Male/female ratio was 2.4/1. 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%.

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.