Cellular neurothekeoma.

We describe the histological and immunohistochemical findings of two cases of cellular neurothekeoma, a recently recognized benign neoplasm considered to be of neural origin. Morphologically they were characterized by a dermal proliferation of plexiform fascicles and small nests of pale eosinophilic, epithelioid or spindle-shaped cells which ramified in an ill-defined pattern between collagen bundles. Scant to moderate amounts of mucin were detected only in the plexiform lobules. Purely myxoid and cellular lobules concurred in these neoplasms. Immunohistochemically, both neoplasms exhibited focal immunoreactivity of the cells for factor XIIIa, providing further evidence for perineural differentiation. Problems of differential diagnosis with other plexiform neoplasms of uncertain origin are discussed.