Primary Care Dermatology Society
The leading primary care society for dermatology and skin surgery

Benign melanocytic naevus

PDF Print E-mail
Latest update 06/12/09

This chapter will focus on the following common benign melanocytic naevi:

  • Acquired melanocytic naevus
  • Dermal naevus
 

Evolution of moles
 
Moles have long since been classified by their histological appearance as being junctional (focal and ‘abnormal’ proliferation of melanocytes at the dermal-epidermal junction), compound (a combination of junctional activity and intradermal naevus cells) and intradermal (groups of mature naevus cells in the dermis only). The evolutionary theory behind these were that naevi progress from junctional to compound and then intradermal. However with the advent of dermoscopy this is now not believed to be the case and instead their appears to be two separate groups of common benign melanocytic naevi:

Acquired melanocytic naevus
  • These are regular moles that appear in the skin at some point after birth
  • The vast majority arise in children and young adults - new lesions are uncommon in patients over the age of 30
  • Shape - tend to be symmetrical and flat or slightly raised
  • Colour - often brown but can be pink or blackish depending on skin type (darker lesions most common in skin types IV-VI). The colour tends to be evenly distributed throughout the lesion or more pronounced in the centre
  • Dermoscopic appearance - the pattern tends to progress from predominantly globular in young people to reticular and then homogenous in older people. Please see the dermoscopy article in the 'Diagnosing Skin Disease' section of the website for more information
Dermal naevus
  • Dermal or intradermal naevi have naevus cell nests in the dermis
  • Shape - thickened and often protrude from the skin surface being either domed shape or papillomatous
  • Colour - lesions tend to be pigmented and lighten with age
  • Dermoscopic appearance - lesions demonstarte a globular / cobblestone pattern. Although in older patients lesions may be relatively banal and show little remaining pigment
  • Patient often worry about catching these lesions and the harm that it may do to the mole. Their is no evidence to suggest that such trauma increases the malignant risk - patients can be reassured that the malignant potential of these moles is very low

Management

  • Approximately half of melanoma cases arise from pre-existing melanocytic naevi - large numbers of melanocytic naevi (common or atypical) therefore represent one of the main risk factors for melanoma
  • The chances of any one individual benign melanocytic naevus becoming malignant is very low and as such prophylactic excision should not be performed
  • Treatment for 'apparantly' harmless moles should only be done if the lesion is causing problems such as catching on clothing. Proud lesions are best removed by shave excision. All samples must be sent for histology
  • Where melanoma is suspected patients must be referred on a 2-week rule to dermatology or plastic surgery


Figure 1 – Multiple acquired melanocytic naevi



(copied with kind permission from Dermatoweb)

Figure 2 – Multiple acquired melanocytic naevi 

Mutiple naevi all showing symmetry in shape and colour



(copied with kind permission from Dermatoweb)

Figure 3 - Close up of an acquired melanocytic naevus

A regular shape. Although there are two colours present these are two shades of brown, and the colour is well-organised in a symmetrical fashion 

Figure 4 - Dermoscopic appearance of an acquired melanocytic naevus

The lesion shows a typical pigment network, which is honeycomb in appearance. Close inspection shows lightening to the edge

Figure 5 - Dermoscopic appearance of an acquired melanocytic naevus

Although not quite as regular as the above a line drawn between 10 and 4 0'clock would still demonstrate symmetry of dermoscopic features. Again the network fades to the edge (black arrow)



(copied with kind permission from the International Dermoscopy Society)

Figure 6 - Acquired melanocytic naevus of the palm  



(copied with kind permission from Dermatoweb)

Figure 7 - Acquired melanocytic naevus

Figure 8 - Dermoscopic appearance of figure 7

Large numbers of regular globules that are even in colour, shape and distribution. This dermoscopic pattern is common in younger patients

Figure 9 - Dermal naevus

Symmetrical, evenly coloured and soft to palpate. Note the hair growing out of the lesion

Although many benign melanocytic naevi may have hairs growing from within them, hairs can occasionally be found in malignant lesions. As a result one must not always presume that hair growth implies the lesion is benign

Figure 10 - Dermoscopic appearance of figure 9

Regular brown dots and globules (arrows)

Figure 11 - Dermal naevus

Figure 12 -Dermoscopic appearance of figure 11

A cobblestone appearance (arrows) is the predominant dermoscopic finding in dermal naevi

Figure 13 – Dermal naevus

This lesion had grown to take on a cerebrieform like appearance

Figure 14 - Dermoscopic appearance of figure 13

A regular cobblestone appearance

Figure 15 - Dermal naevus

Figure 16- Dermoscopic appearance of figure 15

Comma vessels (black arrow) present. Note the milia-like cysts (green arrow) and comedo-like openings (white arrow), which are more frequently seen in seborrhoeic keratoses

Figure 17 - Dermal naevus

Figure 18 - Dermal naevus on cheek

Figure 19 - Dermoscopic appearance of figure 18

As patients get older many naevi will loose their pigment - only a small amount of pigment remains in this naevus (arrow)