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DermNet NZ


Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Moles

What is a mole?

Moles are common skin lesions. They are correctly called melanocytic naevi (American spelling ‘nevi’), as they are due to a proliferation of the pigment cells, melanocytes. If they are brown or black in colour, they may also be called pigmented naevi. Moles are benign in nature (harmless), but a malignant melanoma (cancerous mole) may arise within a mole.

Naevi may form from other skin cells (e.g. vascular naevi are formed from blood vessels), but only those derived from melanocytes are known as moles.

What do moles look like?

Moles may be flat or protruding. They vary in colour from pink or flesh tones to dark brown or black. Although mostly round or oval in shape, they are sometimes unusual shapes. They range in size from a couple of millimetres to several centimetres in diameter.

The number of moles a person has depends on genetic factors and on sun exposure; most white-skinned New Zealanders have 20-50 of them. People with a greater number of moles have a higher risk of developing melanoma than those with few moles, especially if they have over 100 of them.

When do moles appear?

One or more moles may be present at birth. These brown birthmarks are more correctly known as congenital melanocytic naevi. If birthmark-like moles appear within the first two years of life, they are sometimes called 'congenital-type' melanocytic naevi.

More frequently moles arise during childhood or early adult life, when they are called acquired melanocytic naevi. Exposure to sunlight increases the number of moles. Teenagers and young adults tend to have the greatest number of moles and there are fewer in later life because some of them slowly fade away.

Classification of melanocytic naevi

The conventional classification of melanocytic naevi depends on light microscopy i.e. their appearance under the microscope (dermatopathology). They are described according to the site of the naevus cells in the skin. Pathologists may also describe congenital melanocytic naevi as superficial (Ackerman naevus), deep (Zitelli naevus) or combined.

Junctional naevus Dermal naevus Compound naevus Combined naevus
Junctional naevi have groups or nests of naevus cells at the junction of the epidermis (outer layer of the skin) and the dermis (inner layer). These tend to be flat colourful moles. Dermal or intradermal naevi have naevus cell nests in the dermis. These moles are thickened and often protrude from the skin surface (papillomatous naevi). They may be pigmented or skin-coloured. Compound naevi have nests of naevus cells at the epidermal-dermal junction as well as within the dermis (compound naevi). These moles have a central raised area and may be surrounded by flat pigmentation. Combined naevus refers to two distinct types of mole within the same lesion – these include common naevi, blue naevi, blue naevi, and Spitz naevi.
Mole: junctional naevus Mole: dermal naevus Mole: compound naevus Combined naevus

More images of moles ...

A new classification of melanocytic naevi relies on their appearance on dermatoscopy, a technique used by dermatologists to evaluate the structure of moles using a hand-held magnification device.

Dermatoscopic patterns of melanocytic naevi
Reticular naevus Globular naevus Blue naevus Starburst naevus
Reticular naevus reveal a lattice of intersecting brown lines. Globular naevus characteristically show aggregated brown oval structures. The blue naevus is a uniform structureless lesion, steel-blue in colour. Starburst naevus reveals radial lines around periphery of lesion.
Dermoscopy: reticular naevus Dermoscopy: globular naevus Dermoscopy: blue naevus Dermoscopy: starburst naevus
Site-related naevus: facial Site-related naevus: acral Naevus with special features Unclassifiable naevus
Facial naevi reveal pseudonetwork around hair follicles Acral naevi (these are on palms and soles) tend to be made up of parallel lines. Naevi with special features include eczematised naevus (illustrated), irritated naevi and halo naevi. The unclassifiable naevus doesn't have any of the other patterns.
Dermoscopy: facial naevus Dermoscopy: acral naevus Dermoscopy: Meyerson naevus
Dermoscopy: unclassifiable naevus

Terminology used to describe moles

Dermatologists and pathologists have given a variety of names to moles.

Congenital melanocytic naevus

Congenital melanocytic naevi are those present at birth (true congenital naevi) or arising soon afterwards (congenital-like or tardive naevi).

Congenital melanocytic naevi
Small congenital naevus Medium congenital naevus Giant naevus Hairy congenital naevus
Small congenital naevi are less than 1.5 cm diameter. Medium congenital naevi are 1.5 to 10 cm diameter. The giant, or bathing trunk naevus, is larger than 20 cm. Hairy congenital naevi grow thick long hairs.
Congenital naevus Congenital naevus Congenital naevus Congenital naevus
Café au lait macule Speckled lentiginous naevus Naevus of Ota Mongolian spot
Café au lait macule is a flat brown patch. Speckled lentiginous naevus is a flat brown patch with darker spots. Naevus of Ota is a bluish brown mark around forehead, eye and cheek. Mongolian spot is a large bluish mark most often seen on buttocks of newborn.
Congenital naevus Congenital naevus Congenital naevus Congenital naevus

Acquired melanocytic naevus

Ordinary moles that appear after birth may be referred to as acquired naevi. They are often a pink, tan, dark brown or blackish colour; darker colours are more typically found in those with darker skin types. Acquired melanocytic naevi are given a variety of names and there is considerable overlap of descriptions.

Naevi may be described as typical or atypical (not typical). Typical moles affect nearly everyone. The term atypical naevus is often used to mean any funny-looking mole. However, some dermatologists use atypical naevus to describe a mole with specific characteristics: large (>5 mm); ill-defined or irregular borders; varying shades of colour; with flat and bumpy components. This type of mole is also called a Clark naevus. They usually occur in fair skinned individuals and may be solitary or numerous.

Acquired melanocytic naevi
Common naevus Naevus in dark skin Atypical naevus Dysplastic naevus
A common naevus is a flat mole with a single uniform colour. In dark skin, naevi are often black in colour. People with multiple atypical naevi are at increased risk of melanoma (cancerous mole). Dysplastic naevus describes an atypical mole that has specific microscopic criteria.
Common naevus or mole Dark naevus Atypical naevi Dysplastic naevus
Blue naevus Cellular naevus Miescher naevus Unna naevus
Blue naevus is a deeply pigmented type of dermal naevus. Cellular naevus is a non-pigmented dermal naevus. Miescher naevus is a dome-shaped smooth dermal naevus often found on the face. Unna naevus is a papillomatous dermal naevus that is in the shape of a raspberry.
Blue naevus Cellular naevus Miescher naevus Unna naevus
Meyerson naevus Halo naevus Spitz naevus Reed naevus
Meyerson naevus is a naevus affected by a halo of eczema/dermatitis. Halo naevus or Sutton naevus has a white halo around the mole. The mole gradually fades away over several years. Spitz naevus or epithelioid cell naevus, is a pink (classic Spitz) or brown (pigmented Spitz) dome-shaped mole that arises in children and young adults. Reed or spindle cell naevus, is a very 5dark-coloured mole with spindle-shaped dermal melanocytes, usually found on the limbs.
Meyerson naevus Halo naevus Spitz naevus Reed naevus
Recurrent naevus Agminated naevus Acral naevus Nail unit naevus
Recurrent naevus refers to the reappearance of pigment in a scar following surgical removal of a mole – this may have an odd shape. An agminated naevus is a cluster of similar moles or freckles. Acral naevus refers to one on the palm or sole. Nail unit naevus causes a uniform longitudinal band of pigment on a nail.
Recurrent naevus Agminated naevus Acral naevus Nail unit naevus
© Dr Ph Abimelec – dermatologue

More images of halo naevi ..

More images of atypical naevi ..

Signature naevi

Signature naevi are defined as the predominant group of naevi in an individual with multiple moles. They share clinical characteristics and may be typical or atypical.

Signature naevi
Solid brown naevus Solid pink naevus Eclipse naevus Cockade naevus
Solid brown naevi have uniform brown pigmentation. Solid pink naevi are seen in fair skinned individuals and lack melanin pigmentation. Eclipse naevus has a ring, or segment of a ring, of darker pigment around a tan or pink centre. Often found in the scalp. Cockade, or naevus en cocarde/cockarde, has a central dark naevus surrounded by concentric circles of light and dark pigmentation like a rosette.
Solid brown naevus Solid pink naevus Eclipse naevus Cockade naevus
Naevus with perifollicular hypopigmentation Fried-egg naevus Lentiginous naevus Naevus with eccentric pigmentation
Naevi with perifollicular hypopigmentation have white spots around each hair. Easier to see by dermoscopy. Fried-egg naevus is a compound naevus with a flat rim of pigment around a bumpy central portion – the bump can be lighter or darker than the pigmented rim. Lentiginous naevi are small, dark brown or black, flat lesions, often with a slightly paler rim – people with multiple lentiginous naevi have been said to have cheetah phenotype. The Bolognia sign refers to a harmless, small area of darker colour on one side of the naevus.
Naevus with follicular hypopigmentation Fried egg naevus Lentiginous naevus Naevus with eccentric pigmentation

Change in a mole

In adults, it is wise to take change in a mole seriously. Malignant melanoma is a cancerous growth occurring in melanocytes (pigment cells). At first a melanoma may look similar to a harmless mole, but in time it becomes more disordered in structure and tends to enlarge.

If a mole changes size, shape or colour, or a new one develops in adult life it should be evaluated by a dermatologist or other doctor with skills in the recognition of skin cancer. The dermatologist may examine the mole by dermoscopy. It is not always possible to tell whether the lesion is a melanoma just be looking at it, so if there is any doubt it may be necessary to cut the mole out for pathological examination.

Moles sometimes change for other reasons than melanoma, for example following sun exposure or during pregnancy. They can enlarge or regress (disappear). In young people, they may develop a white patch before beginning to fade; this is called a halo naevus.

How is the diagnosis made?

Moles are usually diagnosed clinically by their typical appearance.

If there is any doubt about the diagnosis, they may be excised for histopathology (biopsy). Partial biopsy is not recommended, as it may miss an area of cancerous change.

Removal of moles

Although most moles are harmless and can be safely left alone, moles may be treated under the following conditions:

Shave biopsy

Treating a protruding mole is simple using a procedure called a shave biopsy. After numbing the skin with local anaesthetic the doctor removes the projecting part of the mole with a scalpel or by electrosurgery (e.g. Surgitron method). The wound heals to leave a flat white mark, but sometimes the colour remains the same as the original mole.

Shave biopsy is sometimes used to remove a flat brown patch or freckle for pathological examination. This is sometimes called saucerisation or tangential excision.

Excision biopsy

Excision biopsy is necessary if the mole is flat or melanoma is suspected. The full thickness of the skin is removed and the wound is sutured (stitched). The specimen should always be sent to the laboratory for pathological examination (histology). The resulting scar may be just a thin line, but is sometimes more noticeable than the mole was.

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 also be removed by electrolysis, laser, or excision of the whole mole.

Skin examinations

Prevention of skin cancer

Sun protection is important to avoid damaging your skin.

Related information

References:

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Author: Dr Amanda Oakley, Dermatologist, Hamilton NZ.

Acknowledgement: Many images have been supplied by MoleMap NZ

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If you have any concerns with your skin or its treatment, see a dermatologist for advice.