BONE METASTASES AS THE PRESENTING MANIFESTATION OF RHABDOMYOSARCOMA IN CHILDHOOD

Rarely, rhabdomyosarcoma can present with bone pain and bone lesions o n radiographs without evidence of a primary tumor. Of 428 children wit h biopsy-proven rhabdomyosarcoma, four presented with radiographic evi dence of bone metastases, but no primary tumor was found on subsequent evaluation. On radiographs, these metastases, located most commonly i n the metaphyses of the extremities and in the spine, displayed a dest ructive or diffusely permeative pattern without sclerotic margins and mimicked the more common neuroblastoma. One patient also had diaphysea l cortical lytic metastases of the tibia. Radiographs defined metastas es of the extremities better than the correlative bone scans. In the s pine, on T2-weighted magnetic resonance (MR) images, metastases displa yed high signal intensity which contrasted with the low-signal-intensi ty marrow in these pediatric patients. On histopathologic examination, metastatic rhabdomyosarcoma was composed of small cells of variable s ize, shape, and growth pattern similar to other round cell tumors. A p ositive desmin immunohistochemical test helped to establish the diagno sis. The radiologist, pathologist, and clinician should be aware of th is unusual presentation of rhabdomyosarcoma so that suitable immunohis tochemical tests are performed and appropriate chemotherapy given.