Solar Keratosis and Its Histological Subtypes

Solar keratosis is defined by the World Health Organization as ‘a common intraepidermal neoplasm of sun-damaged skin characterized by variable atypia of keratinocytes.’

Subtypes that are recognised are hypertrophic, atrophic, acantholytic, pigmented. lichenoid and bowenoid. All subtypes usually display the common features of hypogranulosis, parakeratosis along with keratinocyte atypia confined to the bottom two layers of the epidermis (basal and spinous). Below is some of the histological features commonly seen in the subtypes apart from the features mentioned above.

HYPERTROPHIC

This variant exhibits hyperkeratosis, acanthosis, papillomatosis, rete ridge elongation, telangiectasia and parakeratosis. The parakeratosis can be seen alternating with the hyperkeratosis.

ATROPHIC

This variant exhibits epidermal atrophy, basal epidermal budding with adnexal extension.

LICHENOID

This variant exhibits exocytosis, keratinocytic vacuolation, keratinocytic apoptosis, colloid bodies, band-like superficial dermal lymphocytic infiltrate and pigment incontinence.

ACANTHOLYTIC

This variant exhibits acantholysis (with possible extension down adnexae), suprabasal clefting and dyskeratosis.

PIGMENTED

This variant exhibits increased pigmentation of atypical keratinocytes with associated dermal melanophages.

BOWENOID

Although most pathologists consider this Bowen’s disease, some say bowenoid solar keratosis exhibits less than full thickness atypia and sparing of follicles.

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