A 90-year-old woman presents with a hard keratotic papule on the right cheek that has grown over 6 months. It is tender to the touch and has a pink base (Figure 176-1). A shave biopsy through the base is consistent with a cutaneous horn derived from a well-differentiated squamous cell carcinoma (SCC). The patient undergoes an elliptical excision at the base of the horn in the office for definitive therapy.
Cutaneous horn on the right cheek of a 90-year-old woman arising from a well-differentiated squamous cell carcinoma. (Reproduced with permission from Jonathan B. Karnes, MD.)
Cutaneous horn is the descriptive morphologic term given to firm keratotic papules that arise from various benign and malignant underlying pathologies and have an appearance similar to an animal horn.
Cutaneous horns are found in both men and women, most commonly in white patients older than 50. The head, neck, and upper extremities are the most common location, following patterns of sun damage.1
ETIOLOGY AND PATHOPHYSIOLOGY
Multiple benign, premalignant, and malignant causes including wart, seborrheic keratosis, actinic keratosis, Bowen disease, and squamous cell carcinoma lead to a final common pathway of retained stratum corneum rich with the keratin responsible for the firm hornlike quality.
A large case series demonstrated premalignant or malignant causes in 39% of cases.2
Likelihood of underlying malignancy increases with patient age and location on sun-damaged skin.1
Associated with many types of skin neoplasms that can retain keratin and produce horns including actinic keratosis, warts (Figures 176-4, 176-5, 176-6), seborrheic keratosis (Figure 176-7), keratoacanthoma (Figure 176-3), sebaceous gland, and basal or squamous cell carcinoma (Figures 176-1, 176-2, 176-3, 176-8). In a case series, actinic keratosis was found in 83.8% of the premalignant cases and squamous cell carcinoma was found in 93.75% of the malignant cases.3
Rare cases have been described in association with metastatic renal cell carcinoma, lymphoma, dermatofibroma, pyogenic granuloma (Figure 176-9), Kaposi sarcoma, and melanoma.4,5
Cutaneous horn in a squamous cell carcinoma in situ just lateral to the eye. (Reprodued with permission from Richard P. Usatine, MD)
Cutaneous horn on the neck of a 43-year-old black man, which grew over several years. The pathologist first read it as a verruca with cutaneous horn, but when it was reviewed by the dermatopathologist the diagnosis was changed to keratoacanthoma with cutaneous horn. (Reprodued with permission from Richard P. Usatine, MD.)