Naevus follicularis keratosus: clinical aspects, histology and histogenesis]

The clinical, histological and histogenetic aspects of naevus follicularis keratosus (NFK) ("naevus comedonicus") are reported. Clinically, NFK appears mostly as linear and unilateral groups of dark comedo-like plugs. Clinical forms include variants with minimal and distinctive deviations from the basic form. Recurrent inflammation is not mandatory. Histological examination reveals keratin-filled infundibula, with granular layers that are always present but though not always equally obvious. This finding corresponds to the mode of keratinization in the follicular infundibulum. Overall, the findings are indicative of a harmartoma of the follicular infundibulum with additional rudimentary sebaceous glands.