Acquired melanocytic naevi are the familiar moles and present in a number of different ways depending on the type of cells and the depth in the skin.
Junctional naevi are flat macules with melanocytes proliferating along the dermo-epidermal border.
Compound naevi have pigmented naevus cells at the dermo-epidermal border and in the dermis, producing a raised brown lesion. The dermal melanocytes may accumulate around the skin appendages and blood vessels and form a band of cells without melanin or more deeply penetrating strands of spindle cells. Proliferating naevus cells may throw the overlying epidermis into folds, giving a papillary appearance.
In a purely intradermal naevus the junctional element is lost, with the deeper cells showing characteristics of neural tissue. Other types of acquired pigmented naevi include the following.
Blue naevus is a collection of deeply pigmented melanocytes situated deep in the dermis, which accounts for the deep slate-blue colour.
Spitz naevus presents as a fleshy pink papule in children. It is composed of large spindle cells and epitheloid cells with occasional giant cells, arranged in "nests". It is benign and the old name ofjuvenile melanoma should be abandoned.
Halo naevus consists of a melanocytic naevus with a surrounding halo of depigmentation associated with the presence of antibodies against melanocytes in some cases. The whole naevus gradually fades in time.
Becker's naevus is an area of increased pigmentation, often associated with increased hair growth, which is usually seen on the upper trunk or shoulders. It is benign.
Freckles or ephelides are small pigmented macules, less than 0-5 cm in diameter, that occur in areas exposed to the sun in fair skinned people. These macules fade during the winter months.
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