Desmoplastic trichilemmoma arising within a nevus sebaceus.

A 74-year-old man presented with a tumor on his scalp that he had since birth. The authors observed a verrucous pink crusted plaque. The tumor was clinically diagnosed as nevus sebaceus and was removed. Histopathologic study showed, arising from nevus sebaceus, a lobular neoplasm with the classic features of trichilemmoma. Desmoplasia was present in the center of the trichilemmomatous area. This description is typical of a special, uncommon type of trichilemmoma that histologically mimics invasive carcinoma.