Cutaneous horn: a potentially malignant entity.

A cutaneous horn is a conical, dense, hyperkeratotic protrusion that often appears similar to the horn of an animal. It is a morphologic designation referring to an unusually cohesive keratinized material, not a true pathologic diagnosis. Cutaneous horns occur in association with, or as a response to, a wide variety of underlying benign, pre-malignant, and malignant cutaneous diseases. The most important common concern is distinguishing a hyperkeratotic actinic keratosis from a cutaneous squamous cell carcinoma. Keratoacanthoma is another cause, as illustrated herein as a projective cutaneous tumor with a fingernail-like appearance. The treatment of choice for cutaneous horns is shave excision with subsequent histopathologic evaluation to rule out underlying malignancy and to guide potential further therapy.