Trichilemmal cysts arising in an extensive comedo naevus.

A 25-year-old male is described who had extensive linear comedo naevi present from birth, involving the face, both sides of the trunk, both arms, one palm, both legs and one sole. Within these lesions multiple trichilemmal cysts were arising giving rise to a zosteriform pattern of skin nodules. Both lesions were confirmed histologically. It is suggested that comedo naevus is a hamartomatous abnormality of the hair follicle in which all layers, including the external root sheath, are involved and from which trichilemmal cysts may arise.