Dermoscopy

Dermoscopy of malignant melanoma CME

Created 2008.

Learning objectives

  • Describe dermoscopic features of malignant melanoma

Introduction

Malignant melanoma may arise from melanocytes found on the skin or rarely from mucosal surfaces, under the nails and in the meninges.

Melanoma may arise from common acquired naevi or from dysplastic naevi. They may also arise from the solar lentigo or atypical lentigo. Most arise de novo. The dermoscopic features are enormously variable. Early melanoma is relatively organised but as time progresses, it becomes more disorganised, and this is reflected by the dermoscopy.

Melanomas have features indicating their melanocytic origin:

  • Network
  • Aggregated brown or black globules
  • Site-specific features e.g. parallel pattern on palms and soles, follicular openings on facial skin

Many other features have been described in melanoma. And they may be relatively featureless.

Dermoscopy of superficial melanoma

By the time in situ and invasive superficial spreading melanoma (SSM) is recognised as a changing or distinctive lesion by the patient or their doctor, it is often large (>6mm). Characteristically, superficial melanoma is asymmetrical and irregular in shape and structure.

Superficial melanomas usually have one or more of the following dermoscopic features:

  • Blue-white veil
  • Multiple brown dots
  • Pseudopods
  • Radial streaming
  • Scar-like depigmentation
  • Peripheral black dots/globules
  • Multiple (5-6) colours, especially red and blue
  • Broad network
  • Focal sharply cut-off border
  • Negative network
  • Irregular vascularity

The blue-white veil is described as an irregular structureless area of confluent blue pigment with a ground glass haze, as if the image were out of focus. It is due to hyperkeratinisation over dense epidermal pigment. Uniform blue-white structures may be observed over some blue naevi and haemangiomas but in melanoma they are focal, asymmetrical and irregular.

Scar-like depigmentation due to regression of melanoma results in irregular white areas that must be distinguished from the uniform peripheral loss of pigment seen in benign halo naevi. It arises in about 50% of melanomas.

Negative network, although a feature of melanoma, may also be found in some benign melanocytic lesions (especially Spitz naevus) and seborrhoeic keratoses.

Some of the structural features may be subtle in early melanoma, as in several examples shown here. Melanoma may be recognised when there are only 2-3 colours in the lesion on dermoscopy (or 1-2 clinically). Deeper melanomas reveal more colours.

Dermoscopic features of melanoma

The Breslow thickness, which measures the thickness of invasion, is measured in millimetres and is the most important prognostic factor.

Lentigo maligna

Lentigo maligna is a special type of melanoma in situ arising on sun damaged sites. The dermoscopic features of lentigo maligna are characterised by:

  • Thick pigmented lines around appendageal openings, sometimes called rhomboidal structures
  • Asymmetric pigmented follicular openings
  • Slate grey dots and globules
Lentigo maligna

Lentigo maligna melanoma (invasive melanoma arising in lentigo maligna) shows the features of lentigo maligna in its in situ component, as well as features typical of invasive melanoma.

Lentigo maligna melanoma

Not all facial melanoma have these characteristics. In the absence of network, there may be amelanotic areas and irregular blotches.

Facial SSM

Lentiginous melanoma

Lentiginous melanoma arises on the trunk and proximal limbs. It is usually diagnosed in the in-situ phase, and most often affects middle-aged and elderly men that have frequently exposed their backs to the sun. There is some argument regarding this entity and whether it can be distinguished from non-malignant atypical junctional hyperplasia or atypical junctional naevus in the elderly. Dermatoscopy may show features of solar lentigo, melanoma in situ and/or superficial spreading melanoma.

  • Irregular shape, structure and colour
  • Grey or brown lines forming polygons (larger than perifollicular rhomboid structures of lentigo maligna)
  • Grey dots
  • Multiple hypopigmented areas
  • Structureless areas
  • Fine pigment network or fingerprinting
Lentiginous melanoma

Compared with lentiginous melanoma, atypical junctional or lentiginous naevus is less atypical and asymmetrical in structure, and does not include polygons or grey structures. But some clinicians and pathologists believe these lesions are just on a spectrum of atypia, and these lesions often have marked asymmetry of structure on dermatoscopy.

Atypical lentiginous naevus

Nested melanoma of the elderly

This type of superficial spreading melanoma has large intraepidermal nests of tumour cells. These result in a globular pattern. The glbules are varied in shape, colour and distribution within the lesion.

Acral melanoma

Acral melanoma (palms and soles) tends to be much deeper than is suspected from its flat nature. Dermoscopically, it is characterised by a broad parallel ridge pattern rather than the benign parallel furrow pattern. The asymmetry and other features of superficial melanoma may be present.

Little white dots on the ridges are sweat ducts (acrosyringia) and confirm palmoplantar location. In melanoma, these dots disappear because the acrosyringia are destroyed by the malignant process.

Acral melanoma

Subungual melanoma is a type of acral melanoma. Early lesions may show widening pigmented bands, irregular in spacing and varying colour (including pink or red in amelanotic melanoma). A positive Hutchinson's sign refers to pigment arising on the skin adjacent to the nail, which is rare in benign naevi. Changes may be observed by dermoscopy before they are evident clinically. Single pigmented bands should be followed by dermoscopy after several months.

Subungual melanoma (dermoscopy unavailable)

Nodular melanoma

Nodular melanoma is often difficult to identify clinically. It can also be missed by dermoscopy if melanoma features are not noted on the periphery of the lesion. The lesion may composed of only two or three colours and these may be distributed fairly symmetrically. Sixty percent of nodular melanoma is amelanotic. Features often include:

  • Isolated globules
  • Blue-grey veil
  • White streaks
  • Irregular linear or dotted vessels

Nodular lesions with suspicious features should be excised rather than followed up – delay may be dangerous. They may resemble seborrhoeic keratosis, basal cell carcinoma or angioma.

Nodular melanoma

Amelanotic melanoma

Amelanotic melanoma can be difficult to diagnose by dermoscopy. It should be considered if there is history of change within an odd-looking pink lesion. There is nearly always a small amount of focal and irregular pigmentation, often on the periphery of the lesion. Atypical vascularity may be a clue, with linear, dotted, corkscrew or polymorphous vessels. Too much pressure by the dermoscopy instrument may obscure the vascular pattern.

Amelanotic melanoma

Desmoplastic melanoma

Dermoscopic structures in desmoplastic melanoma may include atypical vascular structures, grey dots, or other melanoma-specific structures. When associated with lentigo maligna, features of lentigo maligna may coexist. This form of melanoma may be difficult to differentiate from dermatofibroma, clinically and on dermatoscopy.

Desmoplastic melanoma

Activity

How do dermoscopic features of melanoma vary with increasing Breslow thickness?

 

Acknowledgements

Online continuing medical education designed for health professionals and students.

Learning objectives will be listed for each topic.

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Acknowledgements  

Developed in collaboration with the University of Auckland Goodfellow Unit in 2007.

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2008.  

Images have been sourced from the following:

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Related Information

References

On DermNet NZ

Books about skin diseases

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