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Melanocytic naevus (‘mole’ or ‘naevus’)
Melanocytic naevi present at birth, in childhood, or in young adults.
• Acquired melanocytic naevi start as flat, evenly pigmented (junctional) naevi in which
melanocytes collect in small groups (nests) along the basal epidermal layer. As
melanocytes migrate down into the dermis, flat moles evolve into raised, evenly
pigmented, dome-shaped papules (compound melanocytic naevi), sometimes hairy.
• Scalp naevi in children may be an early sign of being ‘moley’. Patients with many
moles tend to have a ‘signature naevus’, i.e. all their moles follow a pigmentation pattern
that is characteristic for that patient. This is more easily visualized using dermoscopy.
• Over time, the epidermal component is lost, and moles change into flesh-coloured or
pale brown papules (intradermal melanocytic naevi), before disappearing in old age. A
new pigmented growth in an elderly patient is much more likely to be a seborrhoeic wart,
solar lentigo (see next section), or melanoma than a melanocytic naevus.
• Congenital melanocytic naevi, usually >1cm in diameter (sometimes large and
disfiguring = bathing trunk naevus) present at birth/early neonatal period. Large
congenital melanocytic naevi >20cm and the presence of multiple satellite naevi are
associated with an increased risk of malignant change and should be monitored.
• Halo naevi: a white ring develops around a benign melanocytic naevus which gradually
disappears, leaving a depigmented macule that usually eventually repigments. halo naevi
are common in adolescence and of no significance. halo naevi in adults (age 40–50 years)
may indicate melanoma elsewhere—check the skin, eyes, and mucosal surfaces.

Lentigo (plural = lentigines)
• Simple lentigines are small, round, flat, evenly pigmented lesions that persist in winter,
unlike freckles. The basal layer of the epidermis has increased numbers of individual
melanocytes.
• Numerous simple lentigines are found in some genetic disorders, e.g. Multiple lentignes
syndrome, Carney complex, Peutz–Jeghers syndrome.
• Solar (senile) lentigines, 3–12mm in diameter, are flat, brown marks present on sun-
damaged skin in older patients.


Mongolian spot
• Slate-coloured macular areas of pigmentation are present in newborns—usually on the
buttocks or sacrum where pigment may simulate a bruise and even be misdiagnosed as a
sign of non- accidental injury.
• Mongolian spots are commonest in black or Asian infants and gradually disappear with
age.
• Melanocytes are deep within the dermis, and therefore pigment appears bluish, rather
than brown.


Blue naevi
• Benign acquired small slate-blue to blue-black macules or papules that present most
often on the dorsum of the hand or on the scalp.
• Melanocytes are present in the dermis, and tumours appear blue, rather than brown.

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