Cutaneous horn is a clinical diagnosis referring to a conical projection above the surface of the skin that resembles a miniature horn. The base of the horn may be flat, nodular, or crateriform. The horn is composed of compacted keratin. Various histologic lesions have been documented at the base of the keratin mound, and histologic confirmation is often necessary to rule out malignant changes. No clinical features reliably distinguish between benign and malignant lesions. Tenderness at the base and lesions of larger size favor malignancy.
Cutaneous horns usually arise on sun-exposed skin but can occur even in sun-protected areas. The hyperkeratosis that results in horn formation develops over the surface of a hyperproliferative lesion. Most often, this is a benign verruca or seborrheic keratosis; or it could be a premalignant actinic keratosis. More than half of all cutaneous horns are benign, and a further 23-37% are derived from actinic keratoses. A malignancy has been reported at the base of a cutaneous horn in up to 20% of lesions.
Benign lesions associated with cutaneous horns include angiokeratoma, angioma, benign lichenoid keratosis, cutaneous leishmaniasis,1 dermatofibroma, discoid lupus,2 infundibular cyst, epidermal nevus, epidermolytic acanthoma, fibroma, granular cell tumor,3 inverted follicular keratosis, keratotic and micaceous pseudoepitheliomatous balanitis, organoid nevus, prurigo nodularis, pyogenic granuloma,4 sebaceous adenoma, seborrheic keratosis, trichilemmoma,5 and verruca vulgaris.6
Lesions with premalignant or malignant potential that may give rise to cutaneous horns include adenoacanthoma, actinic keratosis, arsenical keratosis, basal cell carcinoma,7 Bowen disease, Kaposi sarcoma, keratoacanthoma, malignant melanoma,8 Paget disease,9 renal cell carcinoma,10 sebaceous carcinoma,11,12 and squamous cell carcinoma.1
Cutaneous horns usually are asymptomatic. Because of their excessive height, they can be traumatized. This may result in inflammation at the base with resulting pain. Rapid growth may occur.
The distribution of cutaneous horn usually is in sun-exposed areas, particularly the face, pinna, nose, forearms, and dorsal hands.17,18 It is a hyperkeratotic papule with the height greater than one-half the width of the base. Usually a cutaneous horn is several millimeters long
Malignant lesions at the base of the horn usually are squamous cell carcinoma, although basal cell carcinoma has been rarely reported. These are predominately precipitated by ultraviolet radiation. Rare tumors at the base include Paget disease of the breast, sebaceous adenoma, and granular cell tumor. The premalignant lesion, actinic keratosis, is a frequent finding at the base. The human papilloma virus most frequently causes infectious etiology resulting in a verruca vulgaris.14 Molluscum contagiosum of the poxvirus group occasionally has formed a cutaneous horn. The only other infectious cause has been leishmaniasis.
Benign idiopathic causes are frequent and include seborrheic keratosis, epidermal nevus, trichilemmal cyst, trichilemmoma, prurigo nodule, and intradermal nevus
Diagnosis is confirmed with a skin biopsy. An adequate specimen usually can be obtained with a simple shave biopsy. The specimen must be of sufficient depth to ensure that the base of the epithelium is obtained for histologic examination.
The horn is composed of compact hyperkeratosis, which may be either orthokeratotic or parakeratotic in nature. Associated acanthosis is a common finding. The base will display features of the pathologic process responsible for the underlying lesion
Treatment recommendation is contingent upon the type of lesion at the base. In order to rule out a malignancy, it is essential to perform a biopsy of the lesion that includes the base of the horn. In the case of benign lesions at the base of the horn, the biopsy is both diagnostic and therapeutic.
- Excise malignancies with appropriate margins. Patients discovered to have horns with an underlying squamous cell carcinoma also should be evaluated for metastasis.
- Local destruction with cryosurgery is first-line treatment for verruca vulgaris, actinic keratosis, and molluscum contagiosum. Benign lesions do not require any further therapy after the diagnostic biopsy