Horn-Like Projection on a Man’s Skull

A cutaneous horn, also known as cornu cutaneum, is a benign keratinized skin tumor characterized by an unusual conical outgrowth from the surface of the skin. This horn-like growth is typically yellowish-white in color and emerges unpredictably from the surface...

Submit your diagnosis to see full explanation.

A cutaneous horn, also known as cornu cutaneum, is a benign keratinized skin tumor characterized by an unusual conical outgrowth from the surface of the skin. This horn-like growth is typically yellowish-white in color and emerges unpredictably from the surface of the skin. The first well-documented case of a cutaneous horn was in an elderly woman named Margaret Gryffith in 1588 in London. Because her condition was so unique, a showman put her on display in an attempt to earn money. This lesion was not recognized in the medical community until 1791, when it was described and operated on by Everard Home^.1 

Cutaneous horns are typically found in sun-exposed areas, including the face, ears, and hands.² Thus, sun exposure is considered to be the major risk factor for their development. These lesions can arise from actinic keratoses and squamous cell carcinomas, and because of this, lighter-skinned individuals are at a greater risk than are individuals with darker skin.² The incidence of cutaneous horns is equal in males and females; however, males have been noted to have a slightly higher incidence of premalignant lesions than age-matched females.³ Also, it is important to note that the risk of cutaneous horn development increases with age, and lesions are most commonly seen in patients who are in their 60s and 70s.³ Although more common in certain individuals, overall, cutaneous horns are considered to be fairly rare.

There are several potential etiologies leading to the development of a cutaneous horn, but common to all is the hyperkeratosis that results from an underlying hyper-proliferative lesion. The specific etiology can be determined by examining the base of the horn. Malignant conditions, such as squamous cell carcinoma, as well as premalignant conditions, such as actinic keratosis, can cause a cutaneous horn to form.^4,5 However, not all cutaneous horns are derived from premalignant or malignant lesions. There are also many benign lesions from which cutaneous horns can arise, some of which include: epidermal nevi, seborrheic keratosis, human papilloma virus-associated verruca vulgaris, molluscum contagiosum, cutaneous leishmaniasis and hypertrophic lichen planus.^6-8 In addition to these associations, there have also been some rare case reports that have documented cornu cutaneum arising from angiokeratomas, psoriasis, discoid lupus, and Kaposi sarcoma. Cutaneous horns are most commonly associated with benign conditions; however, underlying premalignant or malignant lesions have been identified in approximately one-third of cases^.2,8-9 

When diagnosing a cutaneous horn, a shave biopsy is the initial step. The biopsy is necessary to identify the underlying etiology that is resulting in horn formation. The biopsy is taken at the base of the horn, and it is crucial that the biopsy goes deep enough to capture the cells in the basal layer of the epithelium so that they can be visualized under microscopy. Characteristic findings observed on histologic examination of cutaneous horns include visualization of keratin derived from the epidermal layer (including a granular layer), compact hyperkeratosis, and associated acanthosi towards the base of the specimen.^2,4,6 Because cutaneous horns can arise from a variety of lesions, the histologic findings at the base of the lesion will be unique to each underlying disease process.² Variations from the typical cutaneous horn histologic findings exist and may include the observation of epidermal hyperplasia without atypia, as well as the presence of deep red granules instead of a granular layer, as in the case of a trichilemmal horn.¹⁰

Treatment for cutaneous horns includes complete excision of the lesion with clear margins, followed by cauterization of the base. Depending on the size of the defect, a skin graft may be required to assist with primary closure. Depending on the etiology of the cutaneous horn, additional treatments may be required, particularly if the underlying lesion is malignant. Depending on the size and location, squamous cell carcinomas with overlying cutaneous horns can be treated by wide local excision or MOHS surgery. Although the removal of the cutaneous horn is important for comfort and cosmetic purposes, the main goal should be identification and appropriate treatment of the underlying disease.²

Our patient described in this vignette was diagnosed with a cutaneous horn based on his clinical examination. He underwent a shave biopsy with subsequent surgical excision of the horn. The histologic results of the biopsy suggested that the horn was due to a malignancy squamous cell carcinoma. The patient was referred for MOHS surgery for definitive treatment of the squamous cell carcinoma. He was extremely satisfied with the horn removal and has not reported any recurrences.

Yelena Dokic, BSA, is a medical student, Joan Fernandez, BS, is a medical student, and Christopher Rizk, MD, is a dermatology resident at the Baylor College of Medicine in Houston.

References

1. Bondeson J. Everard Home, John Hunter, and cutaneous horns: a historical review. Am J Dermatopathol. 2001;23:362-369.
2. Phulari RG, Rathore R, Talegaon TP, Shah A. Cutaneous horn: A mask to underlying malignancy. J Oral Maxillofac Pathol. 2018;22(Suppl 1):S87-S90.
3. Yu RC, Pryce DW, Macfarlane AW, Stewart TW. A histopathological study of 643 cutaneous horns. Br J Dermatol. 1991;124:449-452.
4. Kusumesh R, Ambastha A, Bhadrapriya, Singh S. Well-differentiated ­squamous cell carcinoma presenting as branched eyelid cutaneous horn: a case report with review of literature. Ind Dermatol Online J. 2017;8:261-263.
5. Park H, Kim W, Kim H, Yeo H. Cutaneous horn in premalignant and malignant conditions. Arch Craniofac Surg. 2016;17:25-27.
6. Bains A, Bagga N, Vedant D, Bhardwaj A, Nalwa A. A case of cutaneous horn arising in verrucous epidermal nevus. Ind J Dermatol Venereol Leprol. 2018 Mar 12.
7. Chen S, Zhou Y, Xia X, Song W. Cutaneous horn masquerading as a seborrheic keratosis. Am J Ophthalmol Case Rep. 201631;4:64-66.
8. Karthikeyan K. Penile cutaneous horn: An enigma-newer insights and perspectives. Indian J Sex Transm Dis. 2015;36:26-29.
9. Kost DM, Smart DR, Jones WB, Bain M. A perforating pilomatricomal horn on the arm of an 11-year-old girl. Dermatol Online J. 2014;16;20:22371.
10. Haro R, González-Guerra E, Fariña MC, Martín-Moreno L, Requena L. Trichilemmal horn: a new case and review of the literature. Actas Dermosifiliogr. 2009;100:65-68.