An Atlas of Lumps and Bumps: Part 23

AFFILIATIONS:
¹Department of Pediatrics, University of Calgary, Calgary, Alberta, Canada
²Alberta Children’s Hospital, Calgary, Alberta, Canada
³Toronto Dermatology Centre, Toronto, Ontario, Canada
⁴Department of Pediatrics and Department of Dermatology and Skin Sciences, University of British Columbia, Vancouver, British Columbia, Canada
⁵Pediatric Dermatology, the Pediatric Institute, Kuala Lumpur General Hospital, Kuala Lumpur, Malaysia

CITATION:
Leung AKC, Barankin B, Lam JM, Leong KF. An atlas of lumps and bumps, part 23. Consultant. 2022;62(12):e11 doi:10.25270/con.2022.11.000010.

DISCLOSURES:
Dr Leung is the series editor. He was not involved with the handling of this paper, which was sent out for independent external peer review.

CORRESPONDENCE:
Alexander K. C. Leung, MD, #200, 233 16th Ave NW, Calgary, AB T2M 0H5, Canada (aleung@ucalgary.ca)

EDITOR’S NOTE:
This article is part of a series describing and differentiating dermatologic lumps and bumps. To access previously published articles in the series, visit https://www.consultant360.com/resource-center/atlas-lumps-and-bumps.

Cutaneous Horn

Cutaneous horn is a clinical diagnosis referring to a conical hyperkeratotic protrusion from the skin that resembles a miniature animal horn (akin to a rhinoceros horn).¹ The horn is composed solely of compacted keratin.^2,3 A cutaneous horn differs from an animal horn by the absence of an axially-positioned, well-formed, bony core.^4,5

Data on the prevalence and incidence of cutaneous horns are lacking.⁶ The condition is most frequently seen among individuals older than 50 years, with a peak between 60 and 80 years.^7,8 Rarely, young children and adolescents may also be affected.^3,9 In this regard, Prabhakar and Bhat³ reported a penile cutaneous horn in a 22-month-old child. The condition is much more common in fair-skinned individuals.^2,10 There is no sex predilection, although there is a higher risk of the lesion being malignant in males.^8,10,11 Predisposing factors include sun exposure (most common), trauma, chronic irritation, burn, radiotherapy, and human papillomavirus infection.^12-16

A cutaneous horn results when an abnormality in the spinous layer of the epidermis leads to excess accumulation of keratin.¹ The condition is regarded as a reactive cutaneous growth caused by a variety of underlying pathology which may be benign, premalignant, or malignant.^7,8 Benign lesions include seborrheic keratosis (most common), lichenoid keratosis, epithelial hyperplasia, scar, verruca vulgaris, molluscum contagiosum, erythema ab igne, discoid lupus, pyogenic granuloma, juvenile xanthogranuloma, angioma, angiokeratoma, epidermal nevus, hypertrophic lichen planus, ichthyosis hystrix, dermatofibroma, pilomatricoma, fibroma, nevus sebaceous of Jadassohn, cutaneous sarcoidosis, histiocystoma, prurigo nodule, trichilemmal cyst, trichilemmoma, granular cell tumor, and inverted follicular keratosis.^2,6,8,17-23 Premalignant lesions include actinic keratosis (most common), pseudoepitheliomatous keratosis, arsenical keratosis, micaceous balanitis, keratoacanthoma, and Bowen disease.^8,24,25 Malignant lesions include squamous cell carcinoma (most common), basal cell carcinoma, verrucous carcinoma, sebaceous carcinoma, Kaposi sarcoma, malignant melanoma, Meckel cell carcinoma, and metastatic carcinoma.^{6,13,24,26-30} In a histological study of 643 cutaneous horns, 61.1% were derived from benign lesions, 23.2% from premalignant lesions, and 15.7% from malignant lesions^.31 As such, the significance of the lesion is not the horn itself but rather the underlying lesion at the base of the horn.

Typically, a cutaneous horn presents as a hard, conical protrusion from the skin surface.⁷ The lesion is slowly progressive and usually asymptomatic unless it is traumatized with resulting pain and inflammation at the base. The color of the lesion can be white, yellow, grey, or brown.^10,32 The size may vary from a few millimeters to several centimeters⁹; cutaneous horns up to 38 centimeters have been reported.^32,33 Typically, the height is at least half of the base diameter.⁹ The shape can be cylindrical, conical, pointed, transversely or longitudinally corrugated, or curved like a ram’s horn (Figures 1-8).^6,9,11,34

Figure 1. A cutaneous horn is shown.

Figure 2. A cutaneous horn presents as a hard protrusion from the skin surface.

Figure 3. The size may vary from a few millimeters to several centimeters.

Figure 4. The color of the lesion can be white, yellow, grey, or brown.

Figure 5. The shape can be cylindrical, conical, pointed, transversely or longitudinally corrugated, or curved like a ram’s horn.

Figure 6. The condition is much more common in fair-skinned individuals.

Figure 7. The condition is most frequently seen among individuals older than 50 years of age.

Figure 8. There is no sex predilection, although there is a higher risk of the lesion being malignant in males.

The base of the horn may be flat, crateriform, or nodular.^7,8,11 Sites of predilection are sun-exposed areas, such as the face, ears, neck, dorsa of hands, forearms, and shoulders.^6,7,9,15 Less commonly, the lesion may also develop in sun-protected areas such as the penis, groin, buccal mucosa, and nasal vestibule^.6,8,35-37 Cutaneous horns are usually solitary, and multiple lesions have rarely been reported.¹⁴

Giant lesions, pain, the presence of pain, tenderness or bleeding at the base, surrounding erythema/inflammation, lesions with a larger width to height ratio, malignancy elsewhere in the body, advanced age, and male sex are associated with a higher chance of there being a malignancy at the base.^1,6,8,14,38

Cutaneous horn is a morphological diagnosis.⁸ An excisional biopsy including the base of the lesion should be performed to confirm the specific diagnosis of the underlying lesion at its base.⁸

Cutaneous horn can be disfiguring and socially embarrassing if the lesion affects a visible area such as the face.³⁹ Patients with lesions on the trunk and extremities may have some discomfort when dressing. Traumatic breakage of the horn, although rare, may occur.¹⁴ When present on the penis, it may interfere with sexual intercourse. More importantly, a cutaneous horn can harbor malignancy. This is especially pertinent if the lesion is on the penile area.^15,40