Melanocytic Naevi and Dysplastic Naevus
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Direct answer
Melanocytic naevi are benign collections of melanocytes, classified as congenital or acquired, and most adults carry many acquired naevi. A dysplastic naevus is a larger, irregular melanocytic naevus with architectural disorder and cytological atypia on histology, and it marks an increased risk of cutaneous melanoma. Sun protection, surveillance and excision of any lesion that changes or looks suspicious form the practical management.
What you must remember
- Congenital naevus: present at birth; large or giant forms carry a higher melanoma risk, and giant axial naevi are linked to neurocutaneous melanocytosis.
- Acquired naevus: junctional naevi are flat and dark, compound naevi are raised and pigmented, and intradermal naevi are raised and skin-coloured.
- Halo naevus: a melanocytic naevus surrounded by a depigmented ring; it is usually benign, is linked to an immune reaction, and often regresses spontaneously.
- Spitz naevus: a dome-shaped, pink or red papule of children and young adults, composed of spindle and epithelioid melanocytes that can mimic melanoma.
- Dysplastic naevus: usually larger than 5 mm, with irregular borders, variegated colour, architectural disorder and cytological atypia on histology.
- Familial risk: CDKN2A mutations are linked to familial melanoma and dysplastic naevus syndrome, where many atypical naevi are seen.
- Management: complete excision with histological examination for suspicious lesions; shave removal is avoided for suspected melanoma.
Sorting a pigmented lesion at the bedside
Most pigmented lesions are benign, so the aim is to recognise the dangerous few. The steps below move from the naevus type to the decision about excision.
- Classify the naevus: note whether it is congenital, acquired, halo, Spitz or dysplastic, and record its size and age of onset.
- Apply ABCDE: check asymmetry, irregular border, colour variation, diameter above 6 mm and evolution, with evolution the most important feature.
- Use dermoscopy: pattern analysis separates benign from atypical lesions, and comparison with the patient's other naevi, the ugly duckling sign, adds to the assessment.
- Count the naevi: a high total number, especially of atypical naevi, raises melanoma risk and calls for closer surveillance.
- Take the family history: a first-degree relative with melanoma or multiple atypical naevi strengthens the indication for review.
- Excise suspicious lesions: complete excision with a narrow margin and histopathology is the standard for a lesion that may be melanoma.
- Follow up: patients with multiple atypical naevi are reviewed regularly, with photographic documentation to track change.
Where the exam tries to catch you
Pigmented lesions are often over-called as melanoma or under-called as harmless, so the traps run in both directions.
- Trap: labelling every large or irregular naevus as melanoma. Correct: dysplastic naevi are benign but atypical, so they are monitored and excised when they change or show severe atypia on histology.
- Trap: treating a halo naevus as a sign of malignant regression. Correct: a halo naevus is typically benign, and the depigmented ring reflects an immune reaction that often resolves.
- Trap: dismissing a dome-shaped red papule in a child as a haemangioma. Correct: a Spitz naevus is a melanocytic lesion that can mimic melanoma, so it needs excision and expert histopathology.
- Trap: shaving a suspicious pigmented lesion to remove it quickly. Correct: shave removal can underestimate depth, so melanoma must be excised with histology to allow Breslow measurement.
Frequently asked questions
What features define a dysplastic naevus?
A dysplastic naevus is usually larger than 5 mm, with irregular borders, variegated colour, architectural disorder and cytological atypia on histology. It is benign but carries a higher risk of melanoma, especially in people with many such naevi.
Which gene is associated with familial dysplastic naevus syndrome?
CDKN2A is the gene most strongly associated with familial melanoma and dysplastic naevus syndrome. Carriers have a substantially higher lifetime risk of melanoma, so family history is an important part of assessment.
How does a Spitz naevus differ from melanoma histologically?
A Spitz naevus typically occurs in children as a dome-shaped, pink or red papule made of spindle and epithelioid melanocytes. Its histology can resemble melanoma, so expert dermatopathology review is needed when the features are unclear.
What is the halo phenomenon around a naevus?
A halo naevus is a melanocytic naevus surrounded by a depigmented ring, and it is usually benign. The depigmentation reflects an immune reaction against melanocytes, and the naevus often regresses spontaneously over time.
When should a melanocytic naevus be excised?
A melanocytic naevus should be excised when it shows features of melanoma, such as recent change in size, shape or colour, or when dermoscopy is suspicious. Excision with histology is preferred over shaving because it confirms the diagnosis and allows accurate measurement of thickness.