Cutaneous epithelioid malignant nerve sheath tumor with rhabdoid features:a histologic, immunohistochemical, and ultrastructural study of three cases

Introduction: Malignant rhabdoid tumors are morphologically defined as shee ts of loosely cohesive cells with eccentric nuclei and hyaline, paranuclear inclusions. Although originally described as a distinctive renal neoplasm of childhood, these tumors have since been described in all age groups and in a variety of extrarenal sites. In the latter setting, it is thought that the rhabdoid phenotype is comprised of histogenetically unrelated tumors, that regardless of histogenesis, pursue a biologically aggressive behavior. Methods: We report on the clinical, histologic, immunophenotypic, and ultra structural characteristics of three cases of cutaneous malignant rhabdoid t umor. Results: Each of the cases arose on the trunk or the extremity of elderly m en. None of the patients had neurofibromatosis. All of the lesions histolog ically showed sheets of loosely cohesive polygonal cells with eccentric nuc lei and hyaline paranuclear inclusions. Each of the cases showed the follow ing immunophenotype: S-100 (+), synaptophysin (+), vimentin (+), alpha smoo th muscle actin (-), CD-30 (-), HMB-45 (-), and pankeratin (-). Ultrastruct ure of two Of the cases yielded similar results showing paranuclear filamen tous aggregates of intermediate filaments, cell membrane dense plaques, and rudimentary cell junctions consistent with nerve sheath differentiation. T onofilaments, dense bodies, microtubules, neurosecretory granules, and mela nosomes were not identified. Each of the patients died of widely metastatic disease within 1 year of diagnosis. Conclusions: Cutaneous epithelioid malignant nerve sheath tumor is a potent ially aggressive tumor capable of showing rhabdoid differentiation thus sim ulating a variety of neoplasms. Immunophenotyping and ultrastructural analy sis reliably discriminates these lesions from melanoma, de-differentiated c arcinoma, lymphoma, and rhabdomyosarcoma. (C) Munksgaard 2000.