By Andrea Cannon, DVM For The Education Center
Originally published in Veterinary Practice News, November 2016 – Download as a PDF
Infundibular keratinizing acanthomas, or keratoacanthomas, are benign neoplasms that are believed to arise from the hair follicle.
Keratoacanthomas are characterized by peripheral proliferation of basaloid epithelial cells with differentiation to squamous epithelium resembling the normal follicular infundibulum / isthmus. They are encapsulated and extend into the panniculus.
In people, a genetic basis for keratoacanthomas has been documented. In dogs, these neoplasms are most commonly seen in Norwegian elkhounds and keeshonds, which may indicate a genetic basis as well. They also have been described in German shepherd dogs, Old English sheepdogs and sporadically in other breeds.
Infundibular keratinizing acanthomas typically involve the trunk, neck and limbs.
Infundibular keratinizing acanthomas (Figure 1) typically involve the trunk, neck and limbs. Although benign, when numerous they cause discomfort and may become infected.
A preliminary diagnosis may be made on clinical examination. Infundibular keratinizing acanthomas are firm to fluctuant, well-circumscribed dermal nodules that vary in size from a half-centimeter to 4 or 5 centimeters. The central pore often is filled with a hard keratinized plug.
A definitive diagnosis is made by submitting an excised nodule for histopathology. Recommended therapies are surgical excision, cryotherapy, electrotherapy and benign neglect. Oral retinoids have been used successfully in some dogs.
When numerous infundibular keratinizing acanthomas are present, surgical excision using a scalpel is not practical as it requires longer anesthesia, wide excisions and sutures.
Here is how an Aesculight CO2 laser may be used to excise numerous infundibular keratinizing acanthomas.
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- Figure 1. A keratinizing acanthoma (pre-op view)
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- Figure 2. Gentle tension is applied and the laser is used to separate the lesion from normal tissue. Note that the incision is kept close to the acanthoma, leaving a smaller defect than would be possible with a scalpel blade.
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- Figure 3. The defect may be sutured after removal or left to heal by secondary intention.
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- Figure 4. The acanthoma is removed intact.
Anesthesia and Pain Management
Start with mild sedation with Dexdomitor and butorphanol and lidocaine SQ for pain control.
Laser Settings
The CO2 laser is set at 12-15 W in the continuous wave mode with a 0.8-millimeter focal spot size. I use higher wattage settings with continuous wave to provide a quicker procedure.
There is more peripheral thermal damage with the continuous wave mode, which may damage any reremaining progenitor cells and help prevent relapse. The surgeon, however, may choose to operate in the pulsed wave mode to ensure minimal thermal damage.
Procedure
First, the laser is used to incise the skin around the base of the acanthoma nodule. The laser incision should be kept maximally close to the base of the lesion.
After the incision is completed, the base or capsule of the infundibular keratinizing acanthoma may be grasped with thumb forceps and elevated to provide gentle tension, thus facilitating excision (Figure 2).
Once the lesion is elevated, the laser is utilized to dissect the infundibular keratinizing acanthoma from the surrounding normal tissue. The surgeon should continue applying gentle tension, while pulling the nodule outward, until the base can be undermined and the acanthoma can be removed intact (Figure 4). The remaining skin defect may be sutured or left to heal by secondary intention.
The CO2 laser permits a conservative excision, and the defect is typically small (Figure 3).
Another benefit of laser surgery is the lack of bleeding at the surgical site, which facilitates the procedure and allows for a more precise incision.
Post-operative pain medications may be prescribed, but typically they are not necessary. Antibiotics are not routinely prescribed.
Dr. Andrea Cannon is a 1993 graduate of the University of California, Davis, where she did her residency in dermatology. She owns Animal Dermatology and Allergy in Rocklin, Calif., and also practices in Modesto, Calif., Fresno, Calif., and Boise, Idaho.
More Reading
- Miller WH, Griffin CE, Campbell KL. “Muller and Kirk’s Small Animal Dermatology, 7th edition.” Saunders-Elsevier, 2013.
- Gross TL, Ihrke, PJ, Walder EJ, Affolter VK. “Skin Diseases of the Dog and Cat: Clinical and Histopathologic Diagnosis, 2nd Edition.” Blackwell Science Ltd., 2005.
This Education Center article was underwritten by Aesculight of Bothell, Wash., the manufacturer of the only American-made CO2 laser.
