RESUMEN
Report a new case of primary Synovi alosarcoma. We report a case of a 16 year old girl, who presented with a tumefaction on the right clavicle evolving or 3 months. Various explorations carried out, in particular thoracic scanner and imagery by magnetic resonance, showed a multilocular cystic formation of the seat and the clavicle reaching the mediastinum. A pathological examination of the part [piece] highlighted a biphasic synovialosarcoma of grade III. This diagnosis was validated by the immunohistochemistry study and the detection of transcribed specific fusion of the synovialosarcoma, SYT-SSXI. The unusual locations of the primitive SS must be known because the diversity of their microscopic aspects may cause confusion in the diagnosis. The immunohistochemistry, and more recently the cytogenetic studies, helps to solve these problems of differential diagnosis