Compound Naevus

See also: Black and brown skin lesions.

This is a form of melanocytic naevus (or mole) that is raised above the surface of the skin and is brown in colour. Melanocytic naevi are considered to be hamartomata if they are congenital. Hamaratomas are tumour-like but non-neoplastic overgrowths of structurally disordered tissue. Compound naevi are considered to be benign neoplasms of melanocytes if they arise in later life.¹

Compound naevi arise from a flat (junctional) naevus that exists earlier in life and may have a raised central portion, of deeper pigmentation with surrounding tan-brown macular pigmentation. Pigmentation may be uneven within the naevus but is usually symmetrically distributed. They are usually of a round/oval shape and roughly 2–7 mm in diameter. They may exist with a variable degree of pigmentation and even be the same colour as the surrounding skin. Their name is derived from the fact that they contain junctional melanocytes (responsible for their pigmentation) and intradermal melanocytes (responsible for the elevation of the lesion).

There are no reliable figures for the prevalence of melanocytic naevi in the general population, but they are exceedingly common in congenital and acquired form. Their prevalence is so high that some believe they cannot even be considered an abnormality or pathological entity, as most people with light-coloured skin will have at least a few.¹ They are much commoner in ethnic groups with light skin but they still have an appreciable prevalence in those with more pigmented skin.

Symptoms

• Establish if the lesion is congenital or acquired (compound naevi are acquired)
• When a lesion presents medically it is important to ascertain whether there have been any associated symptoms such as:
  • Enlargement
  • Change in shape or size
  • Change in pigmentation
  • Itchiness/pain/irritation
  • Bleeding.

Signs

• Examine the lesion in bright light, preferably daylight if available.
• Use drawings or photography to note the site(s), size and pigmentation of the lesion.
• Establish that the lesion has the typical pattern of pigmentation and is raised from the level of the skin.
• Distinguish from other similar raised benign tumours of the skin:
  • Dermatofibromas tend to feel firm or hard on palpation, whereas compound naevi are softer.
  • Seborrhoeic warts tend to have a 'stuck-on' appearance, rather than blending into the surrounding skin.
  • Melanoma tends to be darker, have an irregular border, be asymmetrical and have recently grown.

• Malignant melanoma
• Lentigines
• Atypical mole (dysplastic naevus)
• Other melanocytic naevi
• Pyogenic granuloma (usually reddish but may be brown)
• Seborrhoeic keratosis
• Acanthoma
• Histiocytoma
• Skin tag (acrochordon)
• Actinic keratosis
• Neuroma
• Squamous cell carcinoma
• Naevi of Ota and Ito.

• No investigations are indicated in the case of a common, acquired compound naevus that has not undergone any recent change.
• Some dermatologists may use dermoscopy to try and distinguish the nature of pigmented lesions.
• If there is any suspicion of malignant melanoma then the investigation of choice is excision biopsy.

• If the diagnosis of compound naevus is clear and there has been no change in a long-standing lesion, then reassurance and monitoring of the lesion are all that is usually required.
• Where there is any doubt as to the diagnosis, perform excision biopsy or refer for dermatological advice.
• Perform excision biopsy whenever the lesion has:
  • Grown
  • Become symptomatic
  • Developed asymmetry
  • Developed an irregular border
  • Altered its degree or pattern of pigmentation
  • Developed satellite lesions.

Compound naevi are benign lesions that do not cause complications and have an excellent prognosis.