Trichilemmal cyst of the upper lip.

We report the apparent first case of a trichilemmal cyst presenting intraorally. Trichilemmal cysts are cysts of epithelial origin with a distinctive keratinization pattern that simulates that of the human anagen hair follicle between bulge and sebaceous gland and in the sac surrounding catagen hairs. This type of keratinization of outer root sheath epithelium occurs when it is freed from its internal cover of inner root sheath. This particular case showed evidence of mild epithelial proliferation and slight foci of "metaplastic" epidermoid keratinization, possibly related to mild trauma. The rarity of intraoral hairs undoubtedly accounts for the lack of reported cases of trichilemmal cysts in oral or perioral locations.