Trichilemmoma arising in the nasal vestibule: report of three cases with special emphasis on the differential diagnosis.

Trichilemmoma is a benign cutaneous epithelial tumor with differentiation towards cells of the outer hair root sheath and usually presents as a small papule on the face of middle-aged or older adults. We herein report three cases of trichilemmoma located in the nasal vestibule, including two of the conventional type and one of the desmoplastic variant. To our knowledge, only one case of trichilemmoma arising in the nasal vestibule has been previously reported. Trichilemmoma must be included in the differential diagnosis of epithelial lesions arising in this location. This is particularly important in the case of the desmoplastic trichilemmoma, a tumor that resembles invasive carcinoma such as desmoplastic squamous cell carcinoma, sclerosing basal cell carcinoma, and trichilemmal carcinoma. The circumscription of the lesion, the architectural pattern of epithelial cell cords and small nests merging with a desmoplastic stroma in the central area of the tumor, the expression of CD34, and the lack of an obvious squamous differentiation or basaloid foci favor the diagnosis of desmoplastic trichilemmoma. All these features help to rule out the diagnosis of carcinoma with significant clinical implications.