Keratinocytic epidermal hamartoma

**Definition:** Keratinocytic epidermal hamartoma or epidermal naevus is a congenital hamartomatous epidermal malformation composed of keratinocytes. It is thought to arise as a result of somatic mutation: early embryonic mutations can give rise to extensive systematised naevi, though typically epidermal naevi are localised linear papillomatous or verrucous plaques. Histologically they exhibit acanthosis, papillomatosis and acanthosis.