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Congenital Melanocytic Naevi

Background

A congenital melanocytic naevus (CMN) is one of many different types of birthmark that may be found in newborn babies:

congenital indicates that the abnormality is present at birth
melanocytic is the adjective derived from the word melanocyte, a type of cell present in normal skin and in certain other organs, whose function is to produce melanin – a brown pigment
naevus is the technical (Greek) word that dermatologists (skin specialists) and paediatricians use to describe any type of birthmark that occurs in the skin, the plural is naevi.

CMNs are classified according to size. A 'small' CMN measures less than 2.5cm across, a 'medium-sized' CMN measures 2.5 to 20cm across, and a 'large' (sometimes called 'giant') CMN will measure over 20cm across. Small CMNs are found in about 1 in 100 newborn babies: it is one of the most common types of birthmark. Medium CMNs occur in approximately 1 in 1,000 newborns; whereas large CMNs only occur in about 1 in 10,000 newborns.

Characteristics of CMNs

Medical text written October 2001 by Dr D Atherton. Last updated November 2006 by Dr D Atherton, Consultant in Paediatric Dermatology, Great Ormond Street Hospital, London, UK.

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