rhabdomyoblastoma

a highly malignant tumor arising in striated muscle or in embryonal mesenchymal cells that exhibit differentiation along rhabdomyoblastic lines, including but not limited to the presence of cells with recognizable cross striations. The pleomorphic form affects predominantly the skeletal muscles of adults; the embryonal-alveolar form occurs mainly in the skeletal muscles of children and young adults, and the embryonal-botryoid form occurs predominantly in tissues of the head, neck, orbit, and urogenital tract of children and young adults.