Melanocytic naevi (moles) are benign proliferations of a specific type of melanocytes called ‘naevus cells’. They are only seldomly present from birth (congenital melanocytic naevi) but manifest themselves throughout life. Naevi are a normal phenomenon and new ones may develop as old ones disappear or grow. Especially during childhood and adolescence, the enlargement and increasing elevation of naevi will take place and can be regarded as a natural process. Sun exposure in childhood, heredity and skin type are factors related to the development of new naevi.
Most naevi remain benign and do not need treatment. They usually do not cause complaints, however, patients may ask for excision for cosmetic reasons. Naevi are mostly presented to the GP to check if they are benign.
Diagnosis is based on the clinical picture and the examination of melanocytic naevi considers their shape, colour, symmetry and size. Naevi have a wide variety of shapes but tend to be less than 6 mm in diameter, symmetric and with even pigmentation, have a round or oval shape, a regular outline, a homogeneous surface and a sharply demarcated border.
The distinction of normal (‘common’ or ‘banal’) naevi from other types of skin proliferations, especially from melanoma (the most serious form of skin cancer) is the focus of the examination. A melanoma only very rarely arises from a common naevus – it mostly appears ‘de novo’.
Atypical naevi (dysplastic naevi) are benign, acquired melanocytic naevi that share some of the clinical features of melanoma such as asymmetry, border irregularities, colour variability, or a diameter of more than 6 mm. The presence of five or more atypical naevi is associated with an increased risk of melanoma. In these cases, a referral to the dermatologist for periodic skin checks is advised.