Melanoma — SCE Dermatology MCQ

Correct answer: C — Acanthotic epidermis with underlying dense aggregates of melanin-laden melanophages and melanin in the dermis

The correct answer is C, acanthotic epidermis with underlying dense aggregates of melanin-laden melanophages and melanin in the dermis. The blue-white veil is a melanoma-specific dermoscopic structure produced when compact orthokeratosis and epidermal acanthosis overlie heavily pigmented melanocytes, melanophages and melanin deposited deep in the dermis. Light scattering through this thickened, pigment-laden tissue (the Tyndall effect) shortens the wavelength reaching the observer's eye, producing the characteristic blue-grey, out-of-focus, ground-glass appearance rather than a sharp brown-black colour. Combined with an irregular pigment network, this finding strongly raises suspicion of invasive melanoma and is one of the recognised melanoma-specific dermoscopic criteria used in UK skin cancer assessment pathways. It typically arises in the raised, palpable part of a lesion where dermal pigment accumulation is greatest. Why the other options are wrong: E. Vascular dilatation: this underlies dermoscopic vascular patterns (dotted, linear-irregular or milky-red vessels), not the blue-white veil, and dilated vessels alone do not produce the blue-grey haze. D. Sebaceous gland hyperplasia: this is the substrate for the yellowish, cobblestone-like structures seen in sebaceous hyperplasia, unrelated to pigment scattering or blue colouration. A. Dermal fibrosis: fibrosis produces white, scar-like regression structures or shiny white streaks, but without dense pigment in the dermis there is no blue hue, since fibrosis alone lacks a chromophore. B. Melanin in the stratum corneum: superficial melanin without acanthosis and deep dermal pigment produces brown surface colour or a pigment network, not the deep-scattering blue-white veil, which requires pigment situated deeper in the dermis under a thickened epidermis. Key point: the blue-white veil arises from the Tyndall effect of light scattering through an acanthotic, hyperkeratotic epidermis overlying dense dermal melanin and melanophages, marking it as a specific (though not sensitive) sign of invasive melanoma.

Reference: DermNet NZ, Dermoscopy of Melanoma (Melanoma-specific dermoscopic criteria: blue-white veil), reviewed 2024, https://dermnetnz.org/cme/dermoscopy-course/dermoscopy-of-melanoma