Imagine a hard, yellowish or brownish conical protrusion, uncannily similar to the horn of an animal, slowly developing on your face, arm or leg, and gradually increasing in size over a period of months or years. How bizarre is that?! This odd condition is known as cutaneous horn (cornu cutaneum in Latin). It occurs most commonly in patients 50 years or older. Certain medieval texts describe the presence of a cutaneous horn as the mark of a witch. The earliest documented case was that of an elderly Welsh woman in London who was displayed commercially as an anomaly of nature in 1588.
The horns are growths composed of keratin, the same tough structural protein that is found in the outermost layer of the epidermis, as well as in your hair and fingernails. They can be conical, pointed or corrugated, straight or curving as a ram's horn. In the majority of cases, the lesion at the bottom of the keratin mound is benign, but in certain cases it may be a malignant tumor, usually a squamous cell carcinoma, or a premalignant condition such as actinic keratosis - thickened, rough, scaly patches of sun-damaged skin.
The most frequent localization of cutaneous horns is on the face or hands (areas with a large degree of sun exposure). Approximately 30% reported cases are located on the upper face and scalp. Madame Dimanche, an elderly French widow living in Paris in the early 19th century, walked around with a horn on her forehead for six years. It reached a whopping length of 24.9 cm (9.8") before it was successfully removed by a surgeon. However, cutaneous horns may also develop in unexpected locations, for example on the penis!
Today, the treatment of choice for cutaneous horns is pretty much the same as it was in the 19th century - surgical excision. Afterwards, histopathologic evaluation of the specimen should be performed to rule out underlying malignancy and to guide potential further therapy.
Below is a photo of a cutaneous horn 5 cm in length which had been growing on the lower eyelid of a 78-year-old farmer for three years. After surgeons removed the growth, the lesion at its base turned out to be a well-differentiated squamous cell carcinoma. The patient had to undergo two additional operations to make sure the entire tumor had been excised, but this particular story ended well - he had no metastases and suffered no relapse.
(Image from: Sadeghi et al. 2012)
And here is another example of a cutaneous horn. This little bastard was growing on the temple of a 76-year-old Korean woman. It was surrounded by a rather large patch of reddened skin and had a a base diameter of 0.7 cm and a height of 2.7 cm. The lesion at its base turned out to be a keratoacanthoma, a relatively common epithelial tumor. It was totally excised and did not recur.
(Image from: Yang et al. 2011)
Fernandes NF, Sinha S, Lambert WC, Schwartz RA. (2009) Cutaneous horn: a potentially malignant entity. Acta Dermatovenerol Alp Pannonica Adriat. 18(4):189–93.
Sadeghi E, Johari HG, Deylami HN. (2012) Eyelid cutaneous horn. J Cutan Aesthet Surg. 2012 Apr-Jun; 5(2):153–154.