Trichilemmal horn: cutaneous horn showing trichilemmal keratinization.

A unique and distinctive clinicopathological entity occurred in nineteen patients who ranged in age from 16 to 72 (median 50) years. Clinically, these were solitary cutaneous horns. Nine were on the limbs, four on the back, two on the face, three on the scalp, and in one the site was not known; the median duration was 2 years. Histologically, there was a benign picture with a protrusion of massive horn and trichilemmal keratinization at the base. This tumour, which I have named trichilemmal horn, must be differentiated from other lesions that show trichilemmal keratinization (trichilemmal cyst, proliferating trichilemmal cyst, keratoacanthoma) and from other cutaneous horns, including trichilemmomal horn (cutaneous horn overlying trichilemmoma).