Birthmarks in pictures

Congenital melanocytic naevus (CMN)

Solitary or multiple, relatively common, flat, often oval lesions. They are usually brown or black and present at birth but may appear later, during the first two years of life. They increase in size with the growth of the child and may thicken as time goes by, occasionally covering a large area. Those less than 1.5cm are said to be small, and those up to 29cm are considered medium-sized. CMN occur in all races. They are genetically determined by an autosomal dominant link and result from a localised proliferation of melanocytes that contribute to skin pigmentation. Any pigmented lesion may raise concerns of malignant melanoma and such a change does occasionally occur in CMN. However, the risk is low in small- or medium-sized lesions but greater for large lesions, those with multiple moles and family history of malignant melanoma. Patients should be warned to report any changes in size or appearance so that if necessary, a check can be made with dermoscopy and biopsy. Should malignant melanoma be confirmed, excision at an early stage should improve the prognosis.