Nasal polyps with atypical stroma cells: a pseudosarcomatous lesion. A light and electron-microscopic and immunohistochemical investigation with implications on the type and nature of the mesenchymal cells.

A case of nasal polyposis with stroma cell atypia in a 33-year-old man is reported. The light microscopic appearance made a rhabdomyosarcoma strongly suspected because of the presence of polymorphous, acidophilic, rhabdomyoblast-like cells. The clinical course was that of an ordinary recurring inflammatory nasal polyp. The ultrastructural and immunohistochemical analysis showed the fibroblastic and histiocytic nature of the atypical cells as being of a probably reactive nature. The reported case illustrates the value of electron microscopy and immunohistochemistry in the evaluation of the true type and nature of atypical mesenchymal cells in pseudosarcomatous lesions.