Trichilemmal horn: case presentation and literature review.

A trichilemmal horn is a histologically unique, uncommonly reported lesion, characterized by a plate-like nodule that extends from the epithelium into the dermis and has a prominent basement membrane. At the periphery of the nodule, there is palisading of basal cells. Trichilemmal keratinization is present in the overlying horn and is composed of orthokeratosis with focal parakeratosis. We describe a 22-year-old white women with a trichilemmal horn on her left elbow and review the literature. With the addition of our patient, trichilemmal horns have been described in 28 patients. They have been observed more often in women (15) than in men (11). The patients ranged in age from 16 to 78 years; more than 60% were 50 years of age or older. Trichilemmal horns were most common on the extremities (12 cases) and the head (11 cases). The diagnosis of a trichilemmal horn should be considered when a cutaneous horn shows trichilemmal keratinization in the absence of dermal inflammation.