title: The many clinico-pathologic faces of actinic keratosis: an atlas.
abstract: Actinic keratoses (AKs) are intraepithelial neoplasms formed by atypical keratinocyte proliferation. Histopathologically, typical AKs are characterized by a slightly thickened epidermis, usually with irregular downward buds, orthokeratosis alternating with parakeratosis ('pink and blue') with loss of the underlying granular layer and a disarrangement of the epidermis with atypical keratinocytes at the basal layer. There are several histopathological variants of AK according to the different degrees of keratinocytic atypia, epidermal hyperplasia/atrophy, inflammation and pigmentation. Some authors consider AK an early in situ squamous cell carcinoma and propose a classification of AK based on the extent of atypical keratinocytes in the epidermis.
authors.affiliation: Department of Dermatology, Medical University of Graz, Graz, Austria.
authors.forename: Cesare
authors.initials: C
authors.lastname: Massone
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Cerroni
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000145:classification / Q000473:pathology*; D003937:Diagnosis, Differential; D006801:Humans; D055623:Keratosis, Actinic / Q000145:classification / Q000473:pathology*; D008488:Medical Illustration; D012878:Skin Neoplasms / Q000145:classification / Q000473:pathology*