Melanocytic naevi

These are a form of melanocytic naevus (or mole) where the accumulation of melanocytes is located predominantly at the dermo-epidermal junction, hence their name. Junctional naevi are often quite darkly pigmented and are macular or very thinly papular with only minimal elevation above the level of the skin.

They are an acquired lesion and as they age they can change their characteristics to that of a compound naevus, where there are accumulations of melanocytes in the dermis and at the dermo-epidermal junction, which causes the lesion to become increasingly papular.

They occur at any site on the body and are regularly shaped, usually round or oval. They are most often uniform in colour and range in pigmentation from light to dark brown. They are usually <7 mm or so in diameter.

Classification of melanocytic naevi

The conventional classification of melanocytic naevi depends on light microscopy i.e. their appearance under the microscope (dermatopathology). They are described according to the site of the naevus cells in the skin.

Junctional naevi have groups or nests of naevus cells at the junction of the epidermis (outer layer of the skin) and the dermis (inner layer). These tend to be flat colourful moles.
Dermal naevi

Dermal or intradermal naevi have naevus cell nests in the dermis. These moles are thickened and often protrude from the skin surface (papillomatous naevi). They may be pigmented or skin-coloured.
Compound naevi

Compound naevi have nests of naevus cells at the epidermal-dermal junction as well as within the dermis (compound naevi). These moles have a central raised area and may be surrounded by flat pigmentation.

They are benign lesions but have the potential to undergo transformation to malignant melanoma.