18.1 Benign Melanocytic Naevi: Acquired, Congenital, Spitz, Blue, Halo & Atypical Naevi
Key Takeaways
- Congenital melanocytic naevi are classed by projected adult size as small (under 1.5 cm), medium (1.5 to 20 cm), large (20 to 40 cm), and giant (over 40 cm), and melanoma risk is concentrated in large and giant naevi.
- Infants with a large or giant congenital naevus with many satellite lesions, or with multiple medium naevi, should be offered brain and spine MRI to look for neurocutaneous melanosis.
- Spitz naevi are typically pink or pigmented dome-shaped papules in children, and dermoscopy often shows a starburst pattern or regular dotted vessels.
- BAP1-inactivated melanocytic tumours are skin-coloured dome-shaped papules and can signal the BAP1 tumour predisposition syndrome, with risks of uveal melanoma, mesothelioma, and renal cancer.
- Having more than about 50 common naevi or several clinically atypical naevi is one of the strongest phenotypic risk factors for cutaneous melanoma.
18.1 Benign Melanocytic Naevi: Acquired, Congenital, Spitz, Blue, Halo & Atypical Naevi
A melanocytic naevus is a benign proliferation of melanocytes in nests. Knowing the normal variants is essential for Session 4 (Dermato-Oncology and Dermoscopy). Melanoma itself is covered in the melanoma chapter.
Acquired Common Naevi
Common naevi appear from early childhood, increase in number until about the third or fourth decade, and then slowly regress. Many start as junctional naevi (nests at the dermo-epidermal junction; flat, evenly brown), become compound (junctional and dermal nests; slightly raised), and finally intradermal (dermal nests only; skin-coloured, dome-shaped, often on the face).
- Driver mutations: BRAF V600E in most acquired naevi, which then enter a stable growth arrest (oncogene-induced senescence).
- Risk marker: having more than about 50 common naevi, or several clinically atypical naevi, is one of the strongest phenotypic risk factors for melanoma.
- Common benign dermoscopic patterns: reticular (network), globular (common in children and on the trunk of young people), homogeneous, and mixed patterns such as reticular centre with peripheral globules. A symmetric rim of peripheral globules is normal in a growing naevus in a child or adolescent, but in older adults it needs monitoring. A patient's naevi tend to look alike (the "signature" naevus); a lesion that differs is the "ugly duckling".
Congenital Melanocytic Naevi (CMN)
CMN are present at birth or appear in the first months. They often show hypertrichosis and texture change. Most are driven by NRAS mutations.
| Category (projected adult size) | Size |
|---|---|
| Small | Under 1.5 cm |
| Medium | 1.5–20 cm |
| Large | 20–40 cm |
| Giant | Over 40 cm |
- Melanoma risk is concentrated in large and giant CMN, especially with many satellite naevi. Melanoma may arise deep in the naevus or in the central nervous system, often in childhood. The risk from small and medium CMN is low.
- Neurocutaneous melanosis: melanocytic proliferation in the leptomeninges, which can cause hydrocephalus, seizures, and CNS melanoma. Offer MRI of the brain and spine (ideally in the first months of life) to infants with large or giant CMN with multiple satellites, or with multiple medium CMN.
- Proliferative nodules within CMN in infancy are usually benign but may need biopsy.
- Management is individual. Prophylactic removal of a large CMN has not been proven to reduce melanoma risk. The aims are regular examination with photographs, prompt biopsy of new nodules, and help with appearance and psychosocial impact.
Spitz and Reed Naevi
| Lesion | Clinical | Dermoscopy | Histology and Genetics |
|---|---|---|---|
| Spitz naevus | Pink, red, or tan dome-shaped papule, usually in children and adolescents, often on the face or legs; grows quickly and then stabilises | Regular dotted vessels (pink types); starburst pattern (pigmented types) | Large epithelioid and/or spindle melanocytes, Kamino bodies. Drivers include HRAS mutations and kinase fusions (ALK, ROS1, NTRK, BRAF) |
| Reed naevus (pigmented spindle cell naevus) | Dark brown-black flat papule, often on the thighs of young women | Starburst pattern | Heavily pigmented spindle melanocytes |
| Atypical Spitz tumour | Larger, asymmetric, or ulcerated | Irregular | Intermediate features; specialist review and complete excision |
In children with a typical symmetric Spitz or Reed pattern, many European experts accept dermoscopic monitoring rather than immediate excision. In adults, and for any atypical or changing lesion, excision is advised because spitzoid melanoma is a mimic.
Blue Naevi
- Dermal proliferation of pigmented dendritic melanocytes, often with GNAQ or GNA11 mutations.
- Clinically blue-grey because deep pigment scatters short (blue) wavelengths (the Tyndall effect).
- Dermoscopy shows homogeneous structureless blue pigment.
- Cellular blue naevi are larger nodules, often on the buttocks or scalp. A new or changing blue lesion in an adult needs excision, because melanoma metastases and nodular melanoma can look similar.
Other Naevus Variants
| Variant | Key Points |
|---|---|
| Halo (Sutton) naevus | A naevus with a white halo from immune destruction, common in adolescents; linked to vitiligo. In an adult, examine the whole skin for melanoma, which can trigger halo reactions |
| Recurrent naevus ("pseudomelanoma") | Pigment regrowth in a scar after incomplete removal; can mimic melanoma on histology, so give the pathologist the previous report |
| Naevus spilus (speckled lentiginous naevus) | A light-brown patch with darker speckles; a small melanoma risk in large lesions |
| Special-site naevi | Genital, breast, ear, flexural, and scalp naevi can show atypical histology while behaving benignly |
| Acral naevi | Dermoscopy shows the parallel furrow, lattice-like, or fibrillar patterns; the parallel ridge pattern suggests acral melanoma |
| Meyerson naevus | A naevus with an eczematous halo |
| Combined and deep penetrating naevi | Mixed populations, including blue-naevus-like components; some carry beta-catenin activation and need expert review |
| Naevi in pregnancy | May darken or enlarge slightly; changing lesions are assessed on the same criteria as at any other time |
Atypical (Dysplastic) Naevi
- Clinically atypical naevi: usually 5 mm or larger, with irregular or blurred borders, variegated colour, and a flat component. Many are benign. They mark a raised melanoma risk, particularly in familial atypical multiple mole melanoma (FAMMM) syndrome, often due to CDKN2A mutations.
- Histology: architectural disorder and cytological atypia. The WHO classification grades dysplastic naevi as low-grade or high-grade.
- Margins: low-grade (mild or moderate) dysplastic naevi with positive margins usually do not need re-excision if the lesion was completely sampled. High-grade (severe) dysplastic naevi are generally re-excised with a small clear margin (several millimetres).
- Removing all atypical naevi prophylactically is not recommended.
BAP1-Inactivated Melanocytic Tumours
These are skin-coloured to pink dome-shaped papules, often multiple, with large epithelioid melanocytes showing loss of BAP1 staining. Germline BAP1 mutations cause the BAP1 tumour predisposition syndrome, with raised risks of uveal melanoma, mesothelioma, renal cell carcinoma, cutaneous melanoma, and basal cell carcinoma. Several such lesions, or a family history of these cancers, should prompt genetic referral.
Practical Management of Naevi
- Total body skin examination with dermoscopy for anyone with many or atypical naevi, a personal or family history of melanoma, or a changing lesion. Imaging tools for surveillance are covered in the non-invasive imaging section.
- Excise a lesion with melanoma-specific dermoscopic features, a lesion that has changed on sequential imaging, an "ugly duckling", or a new pigmented lesion in an older adult. For flat lesions without melanoma features, a short-term (about 3-month) digital dermoscopy review can detect change.
- Excise suspicious lesions completely (a 1–3 mm margin), orient the specimen, and give the pathologist a clinical description.
- Teach self-examination and sun protection.
A 7-year-old girl has a 6 mm symmetrical pink dome-shaped papule on her cheek that appeared 4 months ago, grew quickly, and has since been stable. Dermoscopy shows regular dotted vessels on a pink background. What is the most likely diagnosis?
A newborn has a giant congenital melanocytic naevus over the back and buttocks, with more than 30 satellite naevi on the trunk and limbs. What investigation should be offered?
A 45-year-old woman has several skin-coloured, dome-shaped papules on her trunk. Histology of one shows large epithelioid melanocytes with loss of nuclear BAP1 staining. Her father had uveal melanoma. Which cancers are associated with the likely inherited syndrome?
A 50-year-old man has a new naevus on his back surrounded by a symmetrical white halo. What is the most appropriate next step?