IMAGING EWINGS-SARCOMA

Ewing's sarcoma is a highly malignant neoplasm of the bone whose origi n is still uncertain. A strong relationship exists between Ewing's sar coma and tumors of neural origin (Ewing family of tumors). Ewing's sar coma must be distinguished from other round-cell tumors like lymphoma and neuroblastoma and also must be differentiated from osteogenic sarc omas. On plain radiographs, Ewing's sarcoma appears as a lytic or mixe d lytic-sclerotic, rarely as predominantly sclerotic lesion with margi ns Lodwick grade III. It is located primarily in the diaphyseal and me tadiaphyseal regions of the long bones of the lower extremities. A lar ge soft tissue tumor is usually present. Magnetic resonance imaging is the imaging modality of choice to evaluate the extent of the primary lesion, to monitor the response to neoadjuvant chemotherapy and to fol low up non-resected Ewing's sarcomas. Bone scintigraphy is necessary t o detect skeletal metastasis, and (201)thallium scanning has been show n to be sensitive in the monitoring of treatment response. Today, comp uted tomography is not longer used to image the tumor site; however,sp iral CT of the lungs plays a central role as a staging and follow-up t ool.