[Recurrent fetal cellular rhabdomyoma:histopathological and ultrastructural observations].

A mass of the neck in an 8-year-old boy diagnosed with recurrent fetal cellular rhabdomyoma was reported.The recurrent tumor consisted of undifferentiated round and short spindle cells and immature striated muscle cells,which was similar to the primary tumor occured in five years ago.However,there were more large round myoblasts which mainly located at the periphery of the tumor and osteoid stroma in the recurrent case immuno-histochemistry stain and ultrstructure observation suggested that these were undifferntiated mesenchymal cell and myoblasts.The differential diagnosis from fibrosarcoma,highly differentiated rhabdomyosarcoma,and hemangiopericytoma were dicussed.Author considered FRMs has a recurrent and malignant change tendency though it belongs to benign tumor.