Trichilemmal horn on burn scar tissue.

We describe the case of a 53-year-old Japanese woman with a trichilemmal horn on burn scar tissue on her left arm. When examined using light microscopy, the lesion showed U-shaped epidermal proliferations which keratinized in a fashion either identical or similar to trichilemmal keratinization. Immunohistochemical results established a relationship between the trichilemmal horn and the outer root sheath of the hair follicle. Trichilemmal keratinization was observed using electron microscopy. Apparently, the tumor had developed on a skin scar where hair follicles were not clinically present. We concluded that the tumor had originated from some hair follicle cells remaining in the epidermis after the burn.