Seborrhoeic keratosis (basal cell papilloma) is an extremely common slowly growing lesion found on the face, trunk and extremities of elderly individuals as a discrete light- to dark-brown plaque with a friable, greasy, verrucous surface and a ‘stuck-on’ appearance (Fig. 1.6A). They are frequently numerous. The differential diagnosis includes pigmented basal cell carcinoma, naevus and melanoma. Histopathology shows expansion of the squamous epithelium of the epidermis by proliferating basal cells, sometimes with keratin-filled horns or cystic inclusions (Fig. 1.6B). Treatment involves shave biopsy (occasionally simple excision), electrodesiccation with curettage, laser ablation, cryotherapy with liquid nitrogen, and chemical peeling.

Actinic (solar, senile) keratosis is a common slowly growing lesion that rarely develops on the eyelids. It typically affects elderly, fair-skinned individuals on areas of sun-damaged skin such as the forehead and backs of the hands, and appears as a hyperkeratotic plaque with distinct borders and a scaly surface that may become fissured (Fig. 1.7A). Occasionally the lesion is nodular or wart-like and may give rise to a cutaneous horn. Histopathology shows irregular dysplastic epidermis with hyperkeratosis, parakeratosis and cutaneous horn formation (Fig. 1.7B). It has potential, though low, for transformation into squamous cell carcinoma. Treatment involves biopsy followed by excision or cryotherapy.

(Courtesy of A Pearson – fig. A; J Harry – fig. B)

A freckle (ephelis, plural ephelides) is a small (generally 1–5 mm) brown macule due to increased melanin in the epidermal basal layer, typically in sun-exposed skin (Fig. 1.8); numbers vary with the level of sun exposure and can sometimes regress completely. Histopathology shows hyperpigmentation of the basal layer of the epidermis, with a normal melanocyte population.

Congenital naevi are uncommon and histologically resemble their acquired counterparts (see below). They are usually small and of uniform colour. Rare variants include a ‘kissing’ or split naevus that involves the upper and lower eyelid (Fig. 1.9A) and may occasionally contain numerous hairs (Fig. 1.9B), and a very large lesion covering an extensive area of the body (“giant hairy naevus” – Fig. 1.9C). Large lesions have the potential for malignant transformation (up to 15%). Treatment, if necessary, involves complete surgical excision.

The clinical appearance and potential for malignant transformation of naevi are determined by their histological location within the skin.

(Courtesy of M Jager – fig. A; J Harry and G Misson, from Clinical Ophthalmic Pathology, Butterworth-Heinemann 2001 – fig. B)

Benign Adnexal Tumours

brown but tends to be relatively uniform throughout (Fig. 1.10C). The naevus cells extend from the epidermis into the dermis (Fig. 1.10D). It has a low malignant potential related to the junctional component.