Extracardiac rhabdomyomas.

Extracardiac rhabdomyomas are divided into three subtypes: adult rhabdomyomas (ARs), fetal rhabdomyomas (FRs) and genital rhabdomyomas (GRs), each of which has characteristic clinicopathologic features that facilitate their diagnosis. Rhabdomyomas are invariably benign and show varying degrees of skeletal muscle differentiation by electron microscopy and immunohistochemistry. The etiology of these lesions is not understood; however, there is cytogenetic evidence to indicate that ARs are probably neoplastic in origin. The differential diagnosis of rhabdomyomas includes granular cell tumors and hibernomas for ARs, rhabdomyosarcomas and fibromatosis for FRs, and sarcoma botryoides and vaginal polyps for GRs. Identification and investigation of these lesions provide opportunity for gaining insight into skeletal muscle tumor differentiation and skeletal-muscle tumors in general.