Dermoscopy of malignant melanoma

Learning objectives
Introduction
Dermoscopy of superficial melanoma
Lentigo maligna
Acral melanoma
Nodular melanoma
Amelanotic melanoma
Activity

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

Irregular structure Broad network (arrow) Melanoma in situ	Irregular structure Blue-white veil Irregular vascularity Melanoma in situ	Irregular shape/structure Broad network Irregular vascularity Melanoma in situ	Blue-white veil Multiple brown dots Broad network Melanoma in situ
Irregular shape/structure Blue-white veil Broad network Focal sharply cut-off border Melanoma in situ	Irregular shape/structure Blue-white veil Brown dots Radial streaming Broad network (arrow) Melanoma in situ	Irregular shape/structure Multiple brown dots Radial streaming (thin arrow) Focal sharply cut-off border Irregular vascularity Melanoma in situ	Irregular structure Blue-white veil Multiple brown dots Radial streaming Multiple (5-6) colours Negative network (green arrow) Irregular vascularity Melanoma in situ
Irregular shape/structure Blue-white veil (blue arrow) Broad network Irregular vascularity Melanoma in situ	Irregular structure Multiple brown globules Negative network (green arrow) Irregular vascularity Melanoma in situ	Irregular shape/structure Blue-white veil (blue arrows) Multiple brown globules Radial streaming (thin arrow) Broad network (black arrow) Melanoma in situ	Irregular shape/structure Brown dots Scar-like depigmentation Melanoma in situ
Irregular shape/structure Scar-like depigmentation Irregular vascularity Melanoma in situ	Irregular shape/structure Scar-like depigmentation Peripheral black dots Multiple (5-6) colours Melanoma in situ	Irregular shape/structure Blue-white veil Brown dots Radial streaming (thin arrow) Broad network (black arrow) 5 colours 0.2mm SSM	Irregular structure Blue-white veil Brown dots Broad network (black arrow) 0.35mm SSM
Irregular structure Multiple brown dots Peripheral black dots Broad network Negative network (green arrow) Irregular vascularity (red arrow) Melanoma 0.4 mm	Irregular shape/structure Multiple brown dots (arrow) Broad network 0.6 mm SSM	Irregular shape/structure Blue-white veil Multiple brown globules Multiple (5-6) colours Focal sharply cut-off border Irregular vascularity 0.7mm SSM	Irregular shape/structure Blue-white veil Multiple brown dots Multiple (5-6) colours Broad network Negative network (green arrow) 0.7 mm SSM
Irregular shape/structure Focal sharply cut-off border 0.75 mm SSM	Irregular shape/structure Blue-white veil Radial streaming Negative network Melanoma	Irregular shape/structure Blue-white veil Multiple brown dots Scar-like depigmentation Peripheral black dots/globules Multiple (5-6) colours Irregular vascularity Melanoma	Irregular shape/structure Multiple brown dots Broadened irregular network Melanoma 0.25mm

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 & 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

Irregular shape/structure Blue-white veil Multiple brown dots Peripheral black globules Multiple (5-6) colours Broad network Irregular vascularity 0.27mm melanoma

Irregular shape/structure Blue-white veil Scar-like depigmentation Multiple (5-6) colours Broad network 0.5mm melanoma

Irregular shape/structure Localised blue-white veil Scar-like depigmentation Multiple (5-6) colours Broad rhomboid network Slate-grey dots 1.13mm melanoma

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

Facial SSM

Irregular shape/structure Irregular vascularity Melanoma in situ

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 and confirm palmoplantar location.

Acral melanoma

Irregular structure Parallel ridge pattern Brown dots Blue-grey veil Melanoma in situ

Irregular structure Blue-grey veil Irregular vascularity 7.5mm invasive melanoma

Irregular structure Multiple colours Blue-grey veil Negative network Irregular clusters of dots

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

Irregular structure Blue-grey veil White streaks Multiple brown dots 1.2mm thickness	Irregular structure Blue-grey veil Multiple brown globules 1.4mm thickness (ulcerated)	Irregular structure Blue-white veil Multiple brown dots/globules Multiple (5-6) colours 2.1mm thickness	Irregular structure Brown globules 3.7mm thickness (ulcerated)
Irregular structure Blue-white veil Multiple colours (5-6) Abnormal vascularity 4 mm thickness	Irregular shape/structure Blue-white veil 8mm thickness (ulcerated)	Irregular shape/structure Amelanotic nodule within black flat plaque Atypical vasculirty	Regular shape Unusual structure Amelanotic Atypical vascularty 1.2 mm thickness

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

Activity

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

 

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