Excerpt from Cutaneous Horn

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Background

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.

Pathophysiology

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. A malignancy has been reported at the base of a cutaneous horn in up to 20% of lesions. More than half of all cutaneous horns are benign.

Benign lesions associated with cutaneous horns include angiokeratoma, angioma, benign lichenoid keratosis, cutaneous leishmaniasis, dermatofibroma, discoid lupus, infundibular cyst, epidermal nevus, epidermolytic acanthoma, fibroma, granular cell tumor, inverted follicular keratosis, keratotic and micaceous pseudoepitheliomatous balanitis, organoid nevus, prurigo nodularis, pyogenic granuloma, sebaceous adenoma, seborrheic keratosis, trichilemmoma, and verruca vulgaris. Lesions with premalignant or malignant potential that may give rise to cutaneous horns include adenoacanthoma, actinic keratosis, arsenical keratosis, basal cell carcinoma, Bowen's disease, Kaposi sarcoma, keratoacanthoma, Paget's disease, renal cell carcinoma, sebaceous carcinoma, solar keratosis, and squamous cell carcinoma.

Mortality/Morbidity

The lesion at the base of the keratin mound is benign in the majority of cases. Malignancy is present in up to 20% of cases, with squamous cell carcinoma being the most common type. The incidence of squamous cell carcinoma increases to 33% when the cutaneous horn is present on the penis. Tenderness at the base of the lesion is often a clue to the presence of a possible underlying squamous cell carcinoma.

Race

Because of the proportion of cutaneous horns that arise from actinic keratoses and squamous cell carcinomas, races with lighter complexions tend to be preferentially affected.

Sex

A sex predilection for cutaneous horn has not been shown consistently. In men, the rate of malignancies at the base of the lesion is increased when compared with age-matched women.

Age

The peak occurrence of cutaneous horn is in persons aged 60 years to mid 70s. Lesions with malignancy at the base occur more frequently in patients aged 70 years or older.

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