Dermoscopy. Dermoscopic features (2024)

Created 2008.

Note: dermatoscopic images in this course are nearly all at the same magnification; the full width of the image is equivalent to 12 millimetres on the patient.

Learning objectives

• Recognise dermoscopic features (colours and structures)

Colours

By dermoscopy, the pigmentation of the lesion is evaluated in terms of colour(s): black, dark brown, tan, grey, steel blue, purple, white, yellow and red.

Colours seen on dermoscopy

Symmetry

Clinically, symmetry may be evaluated in terms of shape. Symmetry of shape suggests a benign lesion, and asymmetry suggests melanoma (the ‘A’ and ‘B’ of the American ABCDE's). However, an odd-shaped lesion may also be benign.

By dermoscopy, symmetry is evaluated in terms of pigment pattern (colour and/or structure). Symmetrical pigment pattern is typical of benign skin lesions. Complete asymmetry suggests the lesion may be malignant, but may also be seen in some atypical naevi.

Uniform pigment may also be called ‘hom*ogeneous’ (benign), and an irregular pattern may be called ‘heterogenous’ (atypical or malignant).

Asymmetry of pattern: evaluate structures and colours not shape

Dermatoscopic structures of melanocytic lesions

Melanocytic lesions are made up of three types of structure.

• Pigment network and/or
• Amorphous structureless areas (blotches) and/or
• Dots and globules

Benign lesions tend to have only one or two of these structural patterns in a symmetrical distribution. Malignant lesions tend to have areas of network, amorphous structures and scattered globules in an atypical distribution.

Pigment network

Pigment network is formed by melanocytes or melanin in basal keratinocytes. Dense pigment rings (the grid) are due to projections of rete pegs or ridges. The paler ‘holes’ are due to projections of dermal papillae.

A fine regular network is seen in some typical and atypical benign melanocytic lesions. In some sites the network is widened (larger ‘holes’). It does not have to occupy the whole lesion.

• Lentigo
• Junctional naevus
• Compound naevus

Regular pigment network

The term ‘pseudonetwork’ is used when annular pigmentation is seen around hair follicles on facial skin. At times on the face, it may be difficult to differentiate benign naevi, lentigo, actinic keratoses, lichenoid keratosis and early lentigo maligna.

Pseudonetwork: facial skin

An atypical or irregular pigment network may be found in atypical or dysplastic naevi and some melanomas.

• Branched streaks are seen in dysplastic naevi and some melanomas.
• Radial streaming or parallel linear extensions at edge of lesion often represent the radial growth phase of melanoma.
• Pseudopods are bulbous projections at the edge of the lesion due to junctional nests of abnormal melanocytes in invasive melanoma
• Thick lines, also known as ‘broadened network’, are characteristic of melanoma, and are accompanied by irregular holes. Lentigo maligna is often characterised by thick lines around appendageal openings, previously referred to as ‘rhomboidal structures’.

Irregular pigment network: red arrows point to branched streaks, black arrows to broadened network, asterisk to streaming, thin arrow to pseudopods

‘Negative pigment network’ refers to a white reticular pattern due to elongated rete pegs. It is a characteristic of melanoma but also sometimes seen in Spitz naevi and some dysplastic naevi. It may resemble the pattern seen in scars on the lower leg (atrophie blanche). It should not be confused with the pale colour separating the globules of a benign naevus.

Negative network

‘Parallel pattern’ refers to the network seen within most melanocytic naevi on palmar and plantar surfaces. It may be helpful to apply ink to the skin surface and then wipe it off, which reveals the furrows.

• Parallel furrow pattern: pigmented furrows
• Lattice pattern: pigmented furrows and lines crossing these
• Fibrillar/filamentous pattern: delicate pigmentation crossing the skin markings
• Parallel ridge pattern: pigmented ridges (white dots represent sweat duct openings). This pattern is highly specific for melanoma in volar sites.

There is no obvious parallel pattern in hom*ogenous-type naevi on volar sites.

Dermoscopy of palmo-plantar melanocytic lesions

Amorphous areas

Diffuse pigmentation without specific structural features is variously described as amorphous areas or blotches.

• Brown blotches may be due to pigment in the basal layer or papillary dermis and arise when the rete ridges are flattened out.
• hom*ogeneous blue pigmentation is seen in blue naevus.

Diffuse amorphous areas

Irregular blotches are sometimes the only dermoscopic feature of melanoma. They may also arise in dysplastic naevi.

Irregular amorphous areas

Dots and globules

Globules are large dots. Dots and globules represent localised pigment. The colour determines their site: black dots are due to free melanin in the stratum corneum, brown globules are due to junctional nests of melanocytes, and blue or grey dots are due to melanophages in the dermis.

• Benign lesions tend to have central black dots and globules.
• Dots associated with a pigment network may be due to pigment on ridges (superimposed on the network grid) or papillae (in the holes).
• Circumferential brown globules are seen in some enlarging dysplastic naevi.
• Uniform globules with squarish or angulated shape are referred to as cobblestone pattern.
• Diffuse blue/grey dots in the absence of a pigment network are characteristic of lichenoid keratosis.
• Clusters of tiny brown dots are characteristic of melanoma.

Dots and globules in benign lesions

Dots and globules in melanoma: yellow arrows

Dermatoscopic structures of non-melanocytic lesions

Dots

Dots may be seen in pigmented basal cell carcinoma and rarely in seborrhoeic keratoses.

Dots in basal cell carcinoma: yellow arrows

Some specific dermoscopic structures are helpful in the diagnosis of non-melanocytic lesions. These include:

• Leaf-like areas
• Blue ovoid masses
• Milia-like cysts
• Fissures and comedo-like openings.

Leaf-like areas

Leaf-like areas are grey, brown or blue shiny, discrete bulbous structures unassociated with a pigment network (structureless). They are seen on the edges of pigmented basal cell carcinoma, when they often have darker areas within them (blue ovoid masses). Some may not appear very like a leaf, in which case they are better known as ‘structureless areas’. The moth-eaten edges of solar lentigos also sometimes appear leaf-like.

Blue ovoid masses

Blue ovoid masses are large discrete pigmented round, oval or bullet-shaped blue structures and are characteristic of basal cell carcinoma. When the structure has radial projections, they are called ‘spoke-wheel areas’. They are often found within leaf-like or structureless areas. Blue blotches that are sometimes seen in melanoma are irregular, less well defined and appear out of focus.

Milia-like cysts

Milia-like cysts are round white or yellow lesions due to intraepidermal keratin. They are characteristically found within a seborrhoeic keratosis. They may also arise within dermal melanocytic naevi, basal cell carcinoma (BCC) and melanoma.

Fissures and comedo-like openings

Comedo-like openings are sometimes called ‘crypts’. They are little craters and tend to be dark brown, like irregular globules. They are often associated with fissures (clefts). They are characteristic of seborrhoeic keratoses, but may also be found in dermal naevi. Rarely, they may be found in melanoma.

Cerebriform structure

A seborrhoeic keratosis may have a cerebriform or brain-like pattern. The pattern is composed of fissures and ridges mimicking the gyri and sulci of the brain.

This is a useful sign in the absence of comedo-like openings or milia-like cysts.

Fingerprint-like structures

These are a descriptive term for tan or dark-brown, fine parallel cord-like structures characteristically seen in seborrhoeic keratoses and solar lentigo. Wider cords are called ‘fat fingers’. Fat fingers are also rarely seen in melanoma.

The border of skin lesions

The clinical characteristic of an irregular edge is often seen in melanoma, but is quite common in benign lesions too and is not very useful in the early diagnosis of melanoma dermoscopically.

The border of a skin lesion can fade out (often seen in atypical naevi) or be sharply demarcated in a small segment (typical of melanoma). The sharp cut-off may also occur all the way around in a regular or irregular pattern.

A ‘moth-eaten’ edge is seen as concave areas at the edge of a lesion. This edge is seen in the ephilis and some flat seborrhoeic keratoses and lentigos (benign and malignant).

Crystalline structures

Crystalline structures are shiny, bright white, parallel or orthoganol or disordered linear streaks or short lines. They are seen by contact or non-contact polarised dermoscopy but are not seen on contact non-polarised dermoscopy. They are due to excessive collagen and may be seen in dermatofibroma, scar, basal cell carcinoma with fibroplasia, squamous cell carcinoma, Spitz naevi and melanoma. The earlier term 'chrysalis' structure was a misnomer.

White shiny areas are characterised by similar bright white structures of non-linear shape. Rosettes are four bright white points grouped together like a four-leaved clover, and are typical of actinic keratosis.

Vascularity of skin lesions

The vascular pattern may be quite distinctive and allow diagnosis of a pink skin lesion, in the absence of pigmentation or dermoscopic structures. If using a contact dermatoscope, take care not to press down on pink lesions, which will exsanguinate the vessels and make diagnosis more difficult.

Blood vessels on dermoscopy

Activity

Look at your own moles or those of a family member using dermoscopy. What colours do you see? Evaluate the moles for the following features:

• Pigment network
• Amorphous areas
• Dots and globules.