A 6-month-old infant has a hyperpigmented hairy patch on the back measuring 22 cm in maximal diameter, present from birth. The lesion does not blanch and shows discrete satellite naevi over the scalp. The single most concerning long-term complication is:

A.	Cutaneous malignant melanoma
B.	Sturge-Weber-like CNS angiomatosis
C.	Recurrent dermatophyte superinfection
D.	Tuberous sclerosis ash-leaf macules

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Correct Answer � A Explanation

Giant Congenital Melanocytic Naevus: Lifetime Melanoma Risk

Giant CMN with satellite naevi = highest priority is melanoma surveillance.

Core Concept

• Congenital melanocytic naevus (CMN) sized by projected adult diameter — small <1.5 cm, medium 1.5–20 cm, large 20–40 cm, giant ≥40 cm (or ≥20 cm head/neck)
• Giant CMN carries a lifetime melanoma risk of 5–10%, with about half of melanomas arising in the first 3–5 years of life
• Risk modifiers: number of satellite naevi (raise risk and signal CNS involvement), posterior axial location (paraspinal, scalp), and presence of neurocutaneous melanosis (leptomeningeal melanocytosis on MRI)
• Management: serial photographic + dermoscopic surveillance, MRI brain/spine in high-risk patterns, prophylactic excision selectively (especially in lesions on the trunk where melanoma risk is highest), parental counselling

Why Cutaneous Malignant Melanoma is Correct

Pathogenesis / Mechanism:

• Activating somatic NRAS mutations in melanocyte precursors during embryogenesis → expanded clone with persistent malignant potential
• Melanocyte burden is enormous compared with normal skin → simple statistical accumulation of additional somatic hits raises melanoma probability

Clinical correlate:

• 22-cm hairy hyperpigmented patch present from birth + scalp satellite naevi → giant CMN with high-risk satellite phenotype → surveillance for melanoma is the dominant long-term concern

Why the Other Options Are Wrong

B. Sturge-Weber-like CNS angiomatosis:

• Sturge-Weber is associated with a port-wine stain (capillary malformation) in the V1 distribution, not a melanocytic naevus
• Discriminator: Vascular malformation, NOT melanocytic; trigeminal V1 distribution rather than back; leptomeningeal angiomatosis is the CNS lesion — different mechanism entirely.

C. Recurrent dermatophyte superinfection:

• Hairy CMN may harbour dermatophytes occasionally, but this is incidental and not the principal concern
• Discriminator: Common, cosmetic, treatable — orders of magnitude less important than melanoma risk.

D. Tuberous sclerosis ash-leaf macules:

• Tuberous sclerosis is associated with hypopigmented ash-leaf macules, shagreen patch, facial angiofibroma — completely different lesion morphology
• Discriminator: HYPO- not hyper-pigmentation; underlying TSC1/2 mutations unrelated to melanocytic biology.

High-yield Recap

• Giant congenital melanocytic naevus (GCMN) = projected adult diameter ≥40 cm (or >20 cm in newborn).
• Lifetime cutaneous melanoma risk: 5–10%, with 50% of melanomas occurring in the first 3–5 years of life — lesions deep in dermis, hard to detect clinically.
• Neurocutaneous melanosis — leptomeningeal melanocytic deposits; risk highest with axial-location GCMN (head/back) and multiple satellite naevi (>20).
• Driver mutation: NRAS Q61K/R most common; BRAF V600E rare in GCMN (frequent in acquired naevi).
• Management: photoprotection, baseline + serial dermatology surveillance with dermoscopy; baseline MRI brain/spine before age 6 months (uses melanin signal in T1).
• Surgical excision considered for melanoma-risk reduction — staged excision with tissue expansion; full excision often impossible — risk reduction modest.
• DDx: small/medium CMN (lower risk), café-au-lait macules, congenital naevus spilus, dermal melanocytosis (Mongolian spot — benign).