Ultrastructural Findings

Electron microscopic examination supports the rhabdomyoblastic differentiation seen on histologic and immunohistochemical examination, with abortive Z-band formation and thick and thin filaments. Chondrocytic differentiation with a loose granular matrix and abundant rough endoplasmic reticulum can be seen. The majority of cells corresponding to the blastematous and spindle cell areas shows little cytoplasm and few distinguishing features and are best described as primitive mesenchymal cells.