Rapidly enlarging conical lesion on the plantar surface

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Rapidly enlarging conical lesion on the plantar surface
Rapidly enlarging conical lesion on the plantar surface

The lesion was a cutaneous horn, or cornu cutaneum, a cohesive, keratotic, protuberant mass arising from the strateum corneum, or “horny layer.” Cutaneous horns are composed of compacted keratin, somewhat similar to nails and hair. They typically develop on areas that have been damaged by sun exposure or burns. The upper part of the face is most commonly affected. Other locations include the nose, scalp, ears, lips, chest, neck, shoulder, and backs of the hands. Development on the sole, as seen in our patient, is very unusual.

The term “cutaneous horn” refers to a reaction pattern of the epidermis, similar to a corn or callus. It is not a specific histologic diagnosis because different types of lesions are seen at the base of the conical hyperkeratosis. The most common is a seborrheic keratosis, but warts, epidermal nevi, actinic keratoses, arsenical keratoses, or squamous cell carcinoma are also seen. Rarely, trichilemmoma or basal cell carcinoma is seen.

The underlying condition is the most important factor when diagnosing a cutaneous horn. While more than 60% of cutaneous horns are benign, they can be associated with malignant or premalignant lesions. Association with skin cancer is highest in older patients and those with a past history of malignancy.

Cutaneous horns vary in size from a few millimeters to several centimeters. Large growths are more commonly derived from a malignancy, and a surgical section that includes the entire base of the lesion is required for accurate diagnosis. Biopsy of pedal lesions may be painful because of the location and limited flexibility of the dermal tissue. Lidocaine with epinephrine should be slowly injected, and numbing solution should be used to expand the dermal layer, allowing for easy removal of the structure without entering the subcutaneous tissues. Leaving the bulk of the dermal tissues intact ensures faster healing and reduces ambulatory limitations.

At the base of our patient's hyperkeratotic growth was a wart. Following deep shave excision, the lesion has not returned.

Dr. Burkhart is clinical professor of dermatology at the University of Toledo College of Medicine in Ohio and clinical assistant professor of dermatology at Ohio University College of Osteopathic Medicine, in Athens.

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