Dysplastic Naevus 
 

An atypical naevus is a mole with abnormal features on examination including:

 

- irregular shape and borders

- varying shades of colour

- may have a mixture of flat and raised components

- size often > 5mm diameter

 

We call these moles ‘dysplastic’ naevi when they have a defined criteria of abnormal features on histological assessment once they have been surgically removed. They are not cancerous themselves, but they can be challenging to distinguish from melanomas. They also have a higher chance of developing into melanomas in the future and are therefore best removed.

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Melanoma-In-Situ

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Melanoma in-situ is an early form of primary melanoma, where malignant cells are confined to the epidermis only, with no opportunity to spread beyond this top layer of skin to anywhere else in the body. Technically this is a pre-cancerous change and is also known as Stage 0 melanoma as per the AJCC classification listed below. This has a very good prognosis and is usually cured by surgical removal with a margin of normal skin around the lesion. However, if not treated appropriately, melanoma in situ can develop into malignant melanoma.

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Malignant Melanoma 

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Malignant melanomas arise when melanoma cells spread beyond the epidermis, to deeper layers of the skin such as the dermis or subcutaneous fat, or beyond this to other parts of the body such as lymph nodes and distant organs.

 

The Breslow thickness, which measures how far a melanoma has grown into the skin, is very important. The thicker the melanoma, the worse the prognosis. The American Joint Committee on Cancer (AJCC) staging classification takes tumour thickness into account, alongside other factors, which are briefly summarised below:

 

Stage 0 / Tis – melanoma in situ, contained to epidermis

Stage 1A – <0.8 mm thick + not ulcerated

Stage 1B – 0-1mm thick + ulcerated OR 0.8 - 2 mm thick + not ulcerated 

Stage 2A – 1-2 mm thick + ulcerated OR 2-4 mm thick + not ulcerated

Stage 2B – 2 - 4 mm thick + ulcerated OR >4 mm + not ulcerated

Stage 2C – > 4 mm + ulcerated

Stage 3 – ‘Locally advanced’ melanoma with spread between primary tumour and regional lymph nodes

Stage 4 – ‘Advanced’ melanoma with metastatic spread beyond regional lymph nodes

 

 

The patient will often have recognised a distinctive new lesion or an established lesion that has changed. The useful ‘ABCDE’ acronym is widely known by the public and clinicians as a way of remembering the clinical features of melanoma.

• Asymmetry 

• Border irregularity

• Colour variability / Change

• Diameter - increase in size, often > 6mm

• Evolving

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Dermoscopic Features 

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Appreciating the dermoscopic features of melanomas is crucial for distinguishing them from benign skin lesions and other skin cancers. Suspicious lesions require urgent surgical removal for accurate diagnosis on histology. Dermoscopic assessment of skin lesions can help to diagnose melanomas at an earlier stage, which is important as these will have a better prognosis. It can be difficult to differentiate melanoma from benign skin lesions such as atypical/ dysplastic naevi, seborrheoic keratosis and solar lentigines by simple clinical examination. The following dermoscopic features are indicative of melanomas and can aid their diagnosis:

 

• Atypical/irregular pigment network: melanomas often exhibit variations in colour, ranging from shades of brown, black, red, blue, grey or white, with irregular holes and varying thickness of lines within the network. The pigment network can display a sharply cut-off border. A negative network can also be seen where the pigment network is hypo/depigmented.

 

• Irregular dots/globules: black or brown, round or oval, variously sized pigmented structures, irregularly distributed within the lesion. Dark dots and globules are commonly seen at the peripheries.

 

• Streaks: radial lines with or without a bulbous projection at their peripheral ending, irregularly distributed at the periphery of the lesion. They may arise from network structures but more often do not. They range from tan colour to black. These can also be known as Pseudopods.

 

• Regression structures: they correspond to a clinically flat part of the lesion and can be a white-scar like depigmented area or a blue-grey pepper-like granule.

 

• Asymmetric structures: unlike most benign moles which are usually symmetrical in shape, melanomas often exhibit asymmetry. This asymmetry can be observed in the irregular distribution of pigment, vessels, and overall structure within the lesion.

 

• "Ugly duckling" sign: this refers to a lesion that looks noticeably different from the surrounding moles on the same individual. By comparing the dermoscopic features of multiple lesions on the same patient, dermatologists can identify any outlier that stands out as an "ugly duckling" and warrants further evaluation for potential malignancy.

 

• Atypical vessels: irregular, disorganized, or polymorphic vessels (more than one type) that differ from the normal vascular pattern observed in benign lesions. These atypical vessels can appear as dotted, linear, or branched structures within the lesion, indicative of the neoangiogenesis process associated with melanoma growth.

 

• Blue-white veils: a hazy or milky bluish-white discoloration seen on the surface of the lesion. This feature is thought to be due to dermal fibrosis or melanin deposition within the lesion, reflecting the invasive nature of melanoma cells into the deeper layers of the skin.

 

 

Dysplastic naevi and melanoma in situ will have less severe versions of the dermoscopic features listed above, with increasing irregularity and disorganisation as you progress towards the melanoma end of the spectrum. It can be difficult to distinguish between these entities clinically and histological diagnosis is therefore essential. Below are examples of annotated dermoscopic images for each type of lesion.