Nevi (Melanocytic, aka "Moles")

OVERVIEW

Variable estimates but 20-50% of melanomas come from pre-existing nevi.
Estimated yearly risk of nevus transforming to a melanoma <1 in 200,000 to 1 in 33,000, depending on demographics (lowest risk in men and women less than 40, highest in men over 60). (12622618)
It appears that although people with higher nevus counts are more likely to develop melanoma (this is different than and in contrast with the majority of nevi occurring on patients with normal nevus counts), they tend to have better prognosis than melanomas developing in patients with normal nevus counts. This does not appear to be completely explained by increased surveillance in patients with more nevi. (25809795)

On the face, nevi are only flat in children. New macular pigmented lesions in adults are extremely unlikely to be nevi. Even flat nevi in children are typically histopathologically compound. (from Dermoscopy Excellence)

Apart from congenital nevi, kids typically don't get acquired nevi until the onset of puberty.

Management Strategy: Small, stable, non-atypical Spitz nevi in children before puberty can be safely monitored with clinical and dermoscopic follow-up every 3–6 months. Annual follow-up is appropriate once stability is established.
Red Flags for Excision: Large (>1 cm), nodular, ulcerated, rapidly evolving, or atypical spitzoid lesions require complete excision due to potential malignancy.
Diagnostic Pitfalls: Spitz nevi can mimic pyogenic granuloma, angioma, or viral warts, and dermoscopic patterns may resemble melanoma, complicating diagnosis.
Sentinel Node Biopsy (SLNB): Controversial and not reliably prognostic in children. SLNB is not routinely recommended for atypical Spitz tumors (AST).

Rarity: Extremely rare before puberty (<1 case per million); lesions often lack typical adult features (ABCDE).
Common Presentation: Amelanotic, nodular, de novo lesions resembling benign conditions (e.g., pyogenic granuloma).
Management:
- Suspicious Lesions: Prompt excision with narrow margins for histopathologic diagnosis.
- Confirmed Melanoma: Wide local excision; SLNB use should be carefully weighed.
Surveillance: Especially after puberty in children with high nevus count, fair skin, sunburn history, or family history of melanoma.

Dermoscopy Use: Widely adopted for pediatric assessment; helpful in conservative management.
Confounders: Features like eccentric hyperpigmentation (Bolognia sign), eclipse nevi (scalp), and benign acral patterns can mimic melanoma but are typically benign.
Blue Nevi & Combined Lesions: Generally benign; excision warranted only for atypical features or diagnostic uncertainty.

The most common pattern observed in acral acquired melanocytic nevi (AMN) in children was the Parallel Furrow Pattern (PFP), found in 73% of the 56 lesions studied.
50% showed PFP alone, and 21% showed it in combination with the Crista Dotted Pattern, known as the “peas-in-a-pod” pattern.
Age-Related Pattern Distribution: The “peas-in-a-pod” pattern was only seen in lesions that appeared before the age of 7, suggesting it may be associated with earlier-onset lesions.
Histopathology of “Peas-in-a-Pod” Pattern: In these lesions, melanin granules were found in both crista profunda limitans (CPL) and crista profunda intermedia (CPI), distinguishing them from typical AMN and supporting similarity to congenital melanocytic nevi (CMN).
Differentiation from Melanoma: Although some patterns like the crista dots may superficially resemble features seen in melanoma (e.g., melanin aggregation on surface ridges), the distribution of melanin differs. In benign patterns like “peas-in-a-pod,” melanin is localized around eccrine pores, unlike the widespread ridge distribution in melanoma.
Lattice-like Pattern (LLP) is Rare: Only 2% of cases showed LLP, which is consistent with previous findings in both acral AMN and CMN in children, suggesting an anatomical or developmental reason for its rarity in this group

Those occurring in the first 3 years of life.
2 types broadly speaking: blue and non-blue nevi.
Only large (>20cm) nevi pose a higher risk of melanoma in childhood.
Many congenital nevi of special sites including acral, subungual, and genital can have very concerning dermoscopic patterns but are nearly universally benign. (this is not the case for congenital nevi of trunk and extremities)

congenital nevi of the nails can look VERY abnormal, but a subungual melanoma of the nail in a child has never been reported.

Small/Medium CMN: Low lifetime melanoma risk (~1%); observation or excision based on clinical features and cosmetic concerns.
- Because of the frequency of small congenital (and low risk), excision is generally not recommended - monitor.
- Medium sized congenital nevi are much less common and also small enough to be excised in many cases, so this is a common choice that is made between patient and provider.
Large/Giant CMN: Higher melanoma risk, particularly in childhood. Regular clinical and dermoscopic follow-up is essential. But they typically are too large to excise.
Neurocutaneous Melanocytosis: Screen high-risk patients (giant CMN, satellite nevi, midline/head/neck involvement) with brain/spinal MRI.