logo Benign melanocytic lesions

Skin lesions

Benign melanocytic lesions

Objectives

  • Describe dermoscopy.
  • Identify and describe common benign melanocytic lesions (freckles and moles).

Key points

  • Dermoscopy is used to differentiate benign pigmented lesions from melanoma.
  • Dermoscopic features of melanoma include multiple colours and irregular pattern of pigmentation and structures.
  • Dermoscopic features of benign melanocytic naevi are single colour and homogenous pattern of pigmentation and structure.
  • Haemangiomas are identified by red or blue lacunes on dermoscopy.
  • Seborrhoeic keratoses are identified by keratin-filled crypts and milia on dermoscopy.
  • Ephelides are freckles appearing in childhood in which there is increased pigmentation within keratinocytes.
  • Lentigines are acquired freckles in which there are increased numbers of melanocytes along the basal layer of the epidermis.
  • Naevus cells of a junctional naevus are in nests on the dermal-epidermal junction; the mole tends to be flat.
  • Naevus cells of a compound naevus are in nests on the dermal-epidermal junction and within the dermis; the mole tends to be elevated.
  • Naevus cells of an intradermal naevus are in nests within the dermis; the mole tends to lose its pigmentation.
  • A blue naevus is a specific type of darkly pigmented intradermal naevus.
  • A halo naevus is surrounded by depigmentation and may in time disappear because of an autoimmune reaction directed against the naevus cells.
  • Atypical naevi are funny moles i.e. large, or with irregular pigmentation or shape.
  • Congenital melanocytic naevi may be small (<1.5cm), medium or large (>20cm). They may be flat (café au lait macules), elevated, or hairy. Larger congenital naevi have an increased risk of transforming into melanoma.
  • A Spitz naevus is a fast growing red or dark brown lesion most often found in children.
  • Complete excision of a naevus suspicious of melanoma is preferable to an incisional biopsy.
  • Pathological examination should be arranged for all melanocytic lesions that are surgically excised.

Dermoscopy

Dermoscopy, dermatoscopy, epiluminoscopy, epiluminescent microscopy (ELM) and skin surface microscopy describe the evaluation of pigmented skin lesions using magnification devices. Dermatologists use dermoscopy to examine pigmented lesions as an aid to the diagnosis of melanoma. Hand-held devices are most common (Dermatoscope®, Episcope®, Dermlite®). Oil-immersion or polarised lenses eliminate surface reflection so that epidermal and superficial dermal structures can be viewed.

There are characteristic features for many pigmented lesions allowing melanoma to be distinguished from seborrhoeic keratoses, pigmented basal cell carcinomas, haemangiomas, freckles and benign melanocytic naevi (moles). Considerable training and experience is required for reliable interpretation of dermoscopic images.

Digital images may conveniently be displayed on a computer using special lenses for still or video camera. Proprietary archiving software is available but specialist interpretation is necessary, as automated systems are not yet considered reliable. It is useful to be able to compare dermoscopic images of a melanocytic lesion taken at different times, as change may indicate malignancy.

Episcope in use

Dermlite

Melanoma: irregular pigmentation, blue-white veil, atypical pigment network

Haemangioma: red-blue lacunes

Melanocytic naevus: uniform pigment network

Blue naevus: steel-blue homogenous pigmentation


Freckles

Freckles (lentigines) are evenly pigmented brown macules.

Clinical features Histology Image
Ephelis Common in redheaded children with fair skin. May fade or disappear in winter and with age.
  • Increased melanin in basal keratinocytes
Lentigo simplex
  • Pigmented elongated rete ridges
  • Increased melanocytes along basal layer
  • Ink-spot variety; dermoscopic view illustrated
Solar lentigo (1) Scattered small brown lesions on sun-damaged areas
  • Pigmented elongated and clubbed rete ridges
  • Increased melanocytes along basal layer
  • Solar elastosis
Solar lentigo (2) Large well-defined oval patch on face in mature individuals

Solar lentigines may appear similar to pigmented solar keratoses (adherent scale and tenderness) or flat seborrhoeic keratoses (dry surface).

Management

The number of lentigines increases with age and can be reduced by careful sun protection.

Providing there is no chance that an individual lesion is a melanoma, the following may be helpful to fade freckles:

Results are variable but sometimes very impressive with minimal risk of scarring.

Resurfacing lasers (carbon dioxide and Erbium:YAG) that vaporise the surface skin, and cryotherapy, should not be used to remove pigmented lesions by non-specialists. Although they may improve the appearance of lentigines, they may instead result in unsightly patchy hypopigmentation or scarring.

Moles

Moles are melanocytic naevi, sometimes called naevocellular naevi. A few will appear in infancy, more in the second decade, and then a smaller number as an adult. Most people have about 20 to 50 moles. Sun exposure promotes a greater number of naevi. They often appear as light brown macules, become darker papules, and may eventually lose their pigmentation. Some include one or two terminal hairs. The number of moles reduces after the age of 50 – they disappear leaving no trace.

Site of melanocytes (naevus cell nests) Clinical image
Junctional naevus Dermal-epidermal junction
Compound naevus Dermal-epidermal junction and dermis
Dermal / intradermal naevus Dermis
Blue naevus Intradermal (heavily melanized)

Copyright R Suhonen

Mongolian spot Intradermal (melanized)

Histology is shown below.

Histology of intradermal naevus

Superficial naevus cells: epithelioid i.e. more cytoplasm, large pale nucleus

Deeper naevus cells: less cytoplasm, small dark nucleus


Congenital pigmented naevi may be small (1-5cm), medium (1.5-20cm) or rarely, giant (bathing trunk variety). The latter have a significantly increased risk of melanoma in the lesion (3%) or within melanocytes in the central nervous system hence surveillance should be lifelong.

Solitary café au lait macules are common but the presence of six or more is strongly suggestive of neurofibromatosis.

Small congenital melanocytic naevus

Medium hairy congenital melanocytic naevus

Giant congenital melanocytic naevus

Café au lait macule in patient with neurofibromatosis


Halo naevi are common in teenagers. A white ring appears around a normal mole, which gradually fades and eventually disappears. Several years later the white mark may disappear. Histologically there is a lichenoid infiltrate.

Multiple halo naevi

Early halo naevus

Original naevus slowly disappearing


Spitz naevi most often arise on the face of children and adolescents. They grow over a period of time, and are often red or black resembling melanoma. In adults, they are often excised to rule this out, and the pathologist may also find it difficult to distinguish the benign Spitz from a melanoma.

Red Spitz naevus in child

Darkly pigmented Spitz naevus


Atypical naevi are “funny-looking” moles. They may be more numerous, varied in colour (usually shades of brown), size (over 4mm diameter), shape, and contour (with an ill-defined border). Atypical naevi may predispose to melanoma, especially in patients with a strong family history of atypical naevi and melanoma (dysplastic naevus syndrome).

Multiple atypical naevi

Atypical naevus with varying pigmentation and irregular shape

Lesion was suspicious for melanoma but proved to be atypical naevus on histology


Management

Most melanocytic lesions can be ignored, as they are harmless. Sun exposure increases the number and degree of atypicality of moles, a good reason for encouraging sun protection.

Moles may be removed for the following reasons:

Surgical removal may entail:

The coarse hair that sometimes grows in a mole can be removed by shaving. Plucking may cause inflammation resulting in a painful lump under the mole. The hair can only be removed permanently by electrolysis, laser epilation or excision of the whole mole.

Skin lesions that have been removed surgically should always be sent for pathology. If there is concern that a lesion could be a melanoma, it should be completely excised. If the lesion is too big for this to be practical or the scar will be unsightly, it is preferable to send the patient to a dermatologist for a specialist opinion.