title: 'Hints' in the horn: diagnostic clues in the stratum corneum.
abstract: The stratum corneum or horny layer is the uppermost layer of the epidermis, and is mainly responsible for the skin's barrier function. In spite of its complexity at the ultrastructural and molecular level, the features accessible to visualization on conventional histology are relatively limited. Nevertheless, knowledge of subtle clues that one may observe in the stratum corneum can prove useful in a wide range of situations in dermatopathology. We herein review a selection of common and rare entities in which the horny layer may reveal significantly important hints for the diagnosis. These clues include parakeratosis and its different patterns (focal, confluent, alternating, associated with spongiosis, epidermal hyperplasia or lichenoid changes), subcorneal acantholysis, infectious organisms in the stratum corneum (including fungal, bacterial and parasitic), thickening or thinning of the stratum corneum and the presence of different kinds of pigment. Even when normal, the horny layer may prove to be useful when seen in association with severe epidermal damage, a combination of features testifying to the acute nature of the underlying pathological process.
authors.affiliation: Department of Dermatopathology, St John's Institute of Dermatology, St Thomas' Hospital, London, UK.|St John's Institute of Dermatology, St Thomas' Hospital, London, UK.
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Cardoso
authors.affiliation: St John's Institute of Dermatology, St Thomas' Hospital, London, UK.
authors.forename: Ophelia
authors.initials: O
authors.lastname: Veraitch
authors.affiliation: Dermatopathology Laboratory, Department of Dermatology, Universita' degli Studi di Milano, Milano, Italy.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Gianotti
authors.affiliation: Oncology Department, Anatomic Pathology Unit, Gaetano Rummo General Hospital, Benevento, Italy.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Ferrara
authors.affiliation: Dermatopathology, University Hospital Città della Salute e della Scienza, Turin, Italy.
authors.forename: Carlo F
authors.initials: CF
authors.lastname: Tomasini
authors.affiliation: Manuraj Singh, Department of Dermatology, St George's University Hospital, London, UK.
authors.forename: Manuraj
authors.initials: M
authors.lastname: Singh
authors.affiliation: Iris Zalaudek, Division of Dermatology, Non-Melanoma Skin Cancer Unit, Medical University of Graz, Graz, Austria.
authors.forename: Iris
authors.initials: I
authors.lastname: Zalaudek
authors.affiliation: Department of Dermatopathology, St John's Institute of Dermatology, St Thomas' Hospital, London, UK.|St John's Institute of Dermatology, St Thomas' Hospital, London, UK.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Stefanato
mesh_terms: D004817:Epidermis / Q000473:pathology*; D006801:Humans; D012871:Skin Diseases / Q000175:diagnosis* / Q000473:pathology*
keywords: histopathology; hyperkeratosis; hypokeratosis; parakeratosis; stratum corneum