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 sheets 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 ultrastructural characteristics of three cases of cutaneous malignant rhabdoid tumor.

RESULTS

Each of the cases arose on the trunk or the extremity of elderly men. None of the patients had neurofibromatosis. All of the lesions histologically showed sheets of loosely cohesive polygonal cells with eccentric nuclei and hyaline paranuclear inclusions. Each of the cases showed the following immunophenotype: S-100 (+), synaptophysin(+), vimentin (+), alpha smooth muscle actin (-), CD-30 (-), HMB-45 (-), and pankeratin(-). Ultrastructure of two of the cases yielded similar results showing paranuclear filamentous aggregates of intermediate filaments, cell membrane dense plaques, and rudimentary cell junctions consistent with nerve sheath differentiation. Tonofilaments, dense bodies, microtubules, neurosecretory granules, and melanosomes 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 potentially aggressive tumor capable of showing rhabdoid differentiation thus simulating a variety of neoplasms. Immunophenotyping and ultrastructural analysis reliably discriminates these lesions from melanoma, de-differentiated carcinoma, lymphoma, and rhabdomyosarcoma.