Desmoplastic trichoepithelioma and intradermal nevus: a combined malformation.

We studied 13 desmoplastic trichoepitheliomas associated with intradermal nevi. Ten intradermal nevi were found among 76 new cases of desmoplastic trichoepithelioma (13%); three additional examples of the combined malformation were seen in consultation. Clinically, desmoplastic trichoepithelioma associated with an intradermal nevus was typically a small, firm or hard, sometimes annular, nodule on the face, particularly the cheek, of a relatively young woman. Microscopically, the combined malformation contained narrow strands of basaloid cells and keratinous cysts in a desmoplastic stroma, intimately mixed with intradermal nests of nevocytes. Melanocytic nevi have been associated with epidermal hyperplasia resembling seborrheic keratoses, follicular cysts, trichostasis spinulosa, syringomas, basal cell carcinomas, and hair follicle formation on the soles. The frequency of the occurrence of intradermal nevus with desmoplastic trichoepithelioma and the close anatomic association of the two elements may indicate that this combined malformation is another example of epithelial induction by melanocytic nevi.