Pilar sheath acanthoma.

A newly recognized, benign follicular tumor occurred in nine patients who ranged in age from 46 to 75 (median, 55) years. The neoplasms were solitary, asymptomatic, skin-colored nodules with a central pore-like opening plugged with keratin. All lesions had been present for years. Eight were on the skin of the upper lip and one was on the forehead. Histologically, a central cystic cavity showing epidermoid keratinization extended from the surface into the deep cutis. Multiple tumor lobules that were composed of hair sheath epithelium extended from the cyst wall into the surrounding corium. This neoplasm, which we have named "pilar sheath acanthoma," must be differentiated from trichofolliculoma and dilated pore.