The scanning power view of epidermal naevus is of an epidermal proliferative process (Figure 1). Low power reveals hyperkeratosis and papillomatosis across the breadth of the specimen (Figures 2 and 3). Epidermal hyperplasia forms finger like projections with the intervening invaginations filled with hyperkeratotic material (Figure 4). Frequently incidental fungal spore forms are seen. Extending below the projections into the dermis are anastamosing thickened cords of acanthotic epidermis (Figure 5). Dermalcollagen and telangiectatic vessels can be seen within the papillary projections (Figures 5 and 6).
A variable inflammatoryinfiltrate may accompany the epidermal changes, more prominent in the inflammatoryverrucous variant.
A number of reported variants exist including acantholytic, porokeratotic, acanthosis nigricans like, Hailey-Hailey disease-like and verrucous.
Differential diagnosis of epidermal naevus
InflammatoryVerrucous Epidermal Naevus (ILVEN): This naevus is likely simply a subtype of the epidermal naevus. In addition to the superficial perivascular or lichenoidlymphocyticinfiltrate specific epidermal changes are recognised. Areas of alternating parakeratosis and orthokeratosis are seen. Beneath the parakeratosis there is hypogranulosis, whereas beneath the orthokeratosis there is hypergranulosis.
Seborrhoeic keratosis: While clinical correlation is essential here, the presence of elongated down-growths of epidermis with some flattening at the base is more in keeping with an epidermal nevus.
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Pathology of the Skin (3rd edition, 2005). McKee PH, J. Calonje JE, Granter SR