title: Soft tissue tumor with prominent leptomeric fibrils and complexes.
abstract: A recurrent soft tissue tumor from the groin in a 37-year-old male is described. The tumor cells contain many leptomeric structures, both fibrils and complexes, but none of the other characteristic features of striated muscle: alternating parallel thick and thin myofilaments with Z-line material. A review of one rhabdomyoma and six rhabdomyosarcomas demonstrates that leptomeric structures are present in large amounts in the rhabdomyoma but are very infrequent in only three of the six rhabdomyosarcomas. A careful search for leptomeric structures is indicated when the ultrastructural diagnosis of either rhabdomyoma or rhabdomyosarcoma is being considered.
mesh_terms: D000328:Adult; D006119:Groin; D006801:Humans; D008198:Lymph Nodes; D008206:Lymphatic Diseases / Q000473:pathology*; D008297:Male; D008854:Microscopy, Electron; D012207:Rhabdomyoma / Q000648:ultrastructure*; D012208:Rhabdomyosarcoma / Q000648:ultrastructure*; D012983:Soft Tissue Neoplasms / Q000648:ultrastructure*