The exact causes leading to the development of a cutaneous horn are still unknown, but radiation damage, chronic sun exposure, xeroderma pigmentosa, chronic skin irritation, or a human papilloma virus-2 infection are possible risk factors.⁴,⁸ Other possibly associated conditions include a history of a skin malignancy elsewhere in the body or a history of systemic malignancies like renal cell carcinoma or Paget disease of the breast.¹ Regardless of the exact predisposing factors, a cutaneous horn results when an abnormality in the spinous layer of the epidermis results in excessive production and accumulation of keratin.⁴

Cutaneous horns may affect any race, age, or sex and can occur anywhere in the body. However, they are more common on sun-exposed areas of elderly fair-skinned men older than 50 years.⁴,⁵,⁶ On the eyelids, cutaneous horns rarely exceed several millimeters in length (height), although elsewhere in the body they may reach up to several centimeters.¹,³ They have a predilection for the face, ears, the dorsum of the hands, or the penis, but eyelid involvement is infrequent, representing a mere 4% of all surgically excised eyelid neoplasms in one recent study that spanned 10 years.⁶ To the best of our knowledge, only three case series about cutaneous horns exist in the literature, which also underlies the rarity of the condition.¹,⁴,⁶ The mean age at presentation is during the seventh decade, but females may present at an earlier age (6th decade). The condition is rare before the age of 40 years, but cases have been reported in the eyelids as early as 6 years of age.⁵,⁶

Cutaneous horns are usually solitary but rarely may be multiple, particularly in patients with compromised immunity.¹,⁴ The upper eyelid is more commonly involved than the lower, and the lateral canthus may be involved as well. Lesions involving the eyelid margin are rare.⁶ Eyelid cutaneous horns average between 0.7 and 0.8 mm in height, but can be larger and rarely exceed 2 cm.⁴,⁶ Cutaneous horns are typically conical in shape but may take many other forms such as pipe-shaped, cylindrical, lobulated, pointed, or trident or they can have an incurved form (Figure 57.1).⁴,⁶ The outer surface of a cutaneous horn may be papillomatous, irregular, verrucous, or smooth and its color may be white, brown, gray, yellow, or tan (Figure 57.2).⁴ The majority of underlying conditions are benign, but premalignant and malignant lesions combined represent between 25% and 36% of the examined specimens.¹,⁶ Although cutaneous horns predominantly involve the eyelids, other rare periocular locations such as the surface of the globe, the skin overlying the lacrimal sac, and the brow are reported.⁴,⁸,⁹