(BQ) Part 1 book "Lecture notes dermatology" presentation of content: Naevi, inherited disorders, pigmentary disorders, bullous disorders, vascular disorders, connective tissue diseases, pruritus, systemic disease and the skin, skin and the psyche, cutaneous drug reactions,.and other contents. | 11 Naevi Ten thousand saw I at a glance William Wordsworth, ‘The Daffodils’ Introduction Naevi are extremely common – virtually everyone has some. We use the word ‘naevus’ to mean a cutaneous hamartoma (a lesion in which normal tissue components are present in abnormal quantities or patterns – see Glossary). This encompasses lesions that are not visible – and therefore not apparent – at birth, even though the cells from which they arise are physically present. The word can give rise to confusion, largely because it is used rather loosely by some writers (. the word for melanocytic naevi may not strictly be applied without further qualification – see later). This is complicated further by some ‘naevi’ being called ‘moles’ or ‘birthmarks’ . Thus, a lump described as a ‘mole’ may be a melanocytic naevus, but may also be any small skin lesion, especially if pigmented – whereas ‘birthmark’ is accurate enough as far as it goes, but many naevi develop after birth. Any component of the skin may produce a naevus, and naevi may be classified accordingly (Table ). We need discuss only the most important: epithelial and organoid naevi, vascular naevi and melanocytic naevi. Naevi arising from cutaneous epthelium and ‘organoid’ naevi These are relatively uncommon developmental defects of epidermal structures: the epidermis itself, hair follicles and sebaceous glands. There are two important types: the epidermal naevus and the sebaceous naevus. Epidermal naevus Circumscribed areas of pink or brown epidermal thickening may be present at birth or may develop during childhood; many are linear. They usually develop a warty surface – often very early on. Very rarely, there are associated central nervous system (CNS) abnormalities. Becker’s naevus presents as a pigmented patch first seen at or around puberty, usually on the upper trunk or shoulder, which gradually enlarges and frequently also becomes increasingly hairy. Sebaceous naevus Sebaceous naevi are easily overlooked
