Ultrastructural comparison between skeletal muscle and cardiac rhabdomyomas.

The electron microscope features of three primary cardiac rhabdomyomas and one skeletal muscle rhabdomyoma arising from the floor of the mouth are compared, along with a review of the previously reported ultrastructural features of skeletal rhabdomyomas. Cardiac rhabdomyoma filaments appear more orderly and have features suggestive of origin from both Purkinje and myocardial fibers. Zebra bodies were seen exclusively in the cardiac rhabdomyomas. In comparison, the extracardiac rhabdomyoma filaments were more disorderly and many cases had hypertrophic Z bands corresponding to the jackstraw or matchstick structures seen with the light microscope. This finding, along with the presence of satellite cells, was not seen in the cardiac rhabdomyomas.