Extraskeletal Ewing sarcoma with computed tomography correlation.

Extraosseous Ewing sarcoma--a rare clinical entity--is described and the radiographic and histologic features discussed. Histologically this type of tumor may be differentiated from other soft tissue malignancies, but the ultrastructural glycogen content of the cytoplasm makes it frequently inseparable from the conventional osseous form of Ewing sarcoma. In spite of the presence of a huge paraosseal mass with bone erosion or periosteal new bone, computed tomography was the only preoperative modality able to provide evidence of non-involvement of the marrow cavity. However, histologic documentation is necessary to prove that one is dealing with a totally extraosseous Ewing sarcoma.