Canine fibroadnexal hamartomas treated by CO₂ laser excision

By David D. Duclos, DVM, Dipl. ACVD For The Education Center
Originally published in Veterinary Practice News, June 2015 – Download as a PDF

Opinions differ on the origin of fibroadnexal hamartomas. Some authors think they result from a response to trauma while others think they may originate as a primary malformation of follicular structures.

These lesions occur in large-breed dogs, most often on the distal extremities around pressure points and interdigital spaces. The lesions are typically solitary, firm and well circumscribed. In this dog, the lesions were multiple and not well circumscribed.

Patient

An 11-year-old female spayed Weimaraner dog was presented with large tumors that involved the two central digits (III and IV) of the right front paw (Figure 1). The tumors had been present for over a year and were getting larger. The dog would chew at them and make them bleed.

The lesions consisted of mostly alopecic masses. The growths covered the top of the distal digits and extended partially around the sides. One mass was so large that the claws were partially covered. The surface of the lesions had polypoid masses with surfaces that varied from smooth to verrucous. Some hair was present in very sparse amounts.

Diagnosis and Treatment Plan

A 6 mm punch biopsy of one of the lesions was taken to rule out the possibility of viral or infectious disease. The biopsy revealed papillary, polypoid epidermal hyperplasia with hyperkeratosis, dermal fibrosis and adnexal hyperplasia, with no evidence of viral cytopathology or exogenous foreign body.

The treatment plan was to surgically remove the lesions with possible removal of the claws in these two digits. The plan was to use CO₂ laser and attempt to save the claws by removing only the tumor and leaving as much of the normal skin as possible to allow closure of the surgical site.

Anesthesia

Anesthesia consisted of propofol induction and sevoflurane for the surgical procedure.

Procedure

The tumors were excised with our Aesculight CO₂ laser using a 0.25 mm spot size tip (the smallest one available) with continuous wave mode at 30 watts. The excision required very high fluence (small laser spot size at high wattage) to cut through the dense tissue that consisted of primarily keratin and collagen, tissues with low water content.

The use of such high fluence enabled quick removal of the tumor and easy visualization of normal underlying structures. The procedure was performed using the following technique:

Excision of the main portion of the mass.

The surgeon made the initial cut counterclockwise toward the digital pad along the visible junction line of the hamartoma and normal tissue. Once the mass was completely circumscribed, a few more laser passes were performed to deepen the incision (see Figures 2, 5 and 6).

Traction tension was applied to facilitate cutting (Figures 3 and 7).

The mass was then undermined completely and removed (shown in Figure 8).

Touch-up excision and ablation.

Once most of the tumor was initially excised, the laser setting was changed to the C3 pulse mode set at 20 watts, and the final removal of abnormal tissue was done on pulse mode P6, set at 8 watts. Using these modes still provided good cutting and ablation but with the pulse mode, we were able to keep the zone of collateral tissue damage to a minimum.

The surgeon excised more abnormal tissue to ensure the complete removal of the mass (Figures 4 and 8). At one point, when hemorrhage occurred the surgeon defocused the laser energy (by increasing the distance between the handpiece and the target tissue). This ensured efficient hemostasis and the surgery continued with excellent visualization of the anatomical structures.

Wound Closure

The tumor on digit IV was 2x2x3 cm and the tumor on digit III was 2x3x6 cm. The tumors had not progressed into the claw folds so it was decided to save the claws and to close the surgical sites. The surgical wounds were closed with 0-Dexon and 3-0 monofilament nylon suture.

The skin was sutured completely on digit III, and on digit IV the skin was closed with a 2-3 mm space in part of the closure (see Figure 9).

Post-op Care

Post-op care involved pain control with deracoxib; systemic antibiotic consisted of cephalexin for the three-week healing period. The dog was kept in an E-collar to prevent self-induced damage to the bandage. The bandage was to be covered with a waterproof covering to keep dry when going outside. Exercise was restricted to short daily walks on leash only.

Follow-up Exam

The paw was kept wrapped during healing, which took three and a half weeks (Figures 10 and 11). The surgical sites had regrown hair and the paw looked completely normal (as shows Figure 12; the photo was taken six months after the surgery).

The dog experienced no further problems with her paws and lived for three more years before dying from congestive heart disease.

Conclusion

Because of the superior ability to control the fluence by changing spot sizes, power setting and the ability to change from continuous wave mode to pulse modes, the surgeon has excellent control to remove abnormal tissue and to prevent unnecessary damage to healthy adjacent structures.

Moreover, because the CO₂ laser coagulates small capillaries (less than 0.5 mm in diameter) in the surgical field, the surgeon has greater control thanks to better visibility in a bloodless surgical field.

Dr. Duclos is a small-animal practitioner from Lynnwood, Wash., where he has been the owner and clinical dermatologist at the Animal Skin and Allergy Clinic since 1991. He completed his residency in veterinary dermatology at the University of Pennsylvania. He also teaches veterinary students from WSU and from Western University of Health Sciences’ Veterinary School in Pomona, Calif.

All Images Courtesy of Dr. Duclos

This Education Center article was underwritten by Aesculight of Bothell, Wash., manufacturer of the only American-made CO₂ laser.