LARGE CELL ACANTHOMA
As is stated in Pinkus' Guide to Dermatohistopathology, this benign type of keratosis is "not exceedingly rare, but rarely diagnosed". The keratinocytes are larger than normal, and the nuclei in the upper levels of the epidermis retain a round or oval outline. The nuclei are 'contrasty' (stand out from the surrounding cytoplasm). Papillomatosis varies from lesion to lesion and may be variable within a given lesion. Lentiginous hyperpigmentation is almost always present, and large cell acanthomas occur on sun exposed areas.
 
Low power view. Papillomatosis is more prominent in the left side of the picture than in the right. This variation in architecture can be seen within a given lesion.
High power view of above. The large, 'contrasty' nuclei retain round or oval outlines in the superficial levels of the epidermis, and there is lentiginous hyperpigmentation.

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