A tumor composed of cells resembling those of the hair matrix, which undergo 'mummification' and may calcify. It is a relatively uncommon tumor, which may occur at any age from infancy. The majority of patients are under 20, and females are affected more than males. The lesion is usually a solitary deep dermal or subcutaneous tumor 3-30 mm in diameter, situated in the head, neck, or upper extremity. (From Rook et al., Textbook of Dermatology, 4th ed, p2401)
