Removal of a rapidly enlarging subcutaneous mass with CO₂ laser

By Jon Plant, DVM, DACVD For The Education Center
Originally Published In Veterinary Practice News, April 2020 – Download as a PDF

In dogs, fibrosarcomas, peripheral nerve sheath tumors, and hemangiopericytomas are collectively classified as soft tissue sarcomas (STSs). Firm tumors often arise under the skin of the head, neck, or extremities, and may develop slowly or rapidly. The tumors often exfoliate sufficiently with fine-needle aspiration or biopsy to yield a diagnostic sample. Tru-Cut, punch, or incisional biopsy may also be used to establish a diagnosis. Although most STSs do not quickly metastasize, they can be locally invasive along facial planes. Together with their predilection for the extremities, this can make complete excision difficult.

Therapy consists of surgical excision. If histopathology shows the tumor was not completely excised, more aggressive surgical excision, radiation therapy, or chemotherapy may be indicated. However, one study found the prognosis for dogs with masses below the stifle or elbow was favorable, even with marginal excision. Radiation therapy has a low complete response rate as a sole therapy, but a high long-term control rate when combined with surgery. Chemotherapy with doxorubicin-based protocols may be considered for high-grade tumors. Low-dose metronomic chemotherapy has also been described in dogs with incompletely resected STSs.

Case

A 12-year-old, 27-kg neutered male, flat-coated retriever mix was presented for a subcutaneous mass cranial to the right tarsus. The 4-cm diameter subcutaneous mass had rapidly enlarged since it was noted several days earlier. Cytology from a fine-needle biopsy revealed low numbers of atypical spindle cells, suggestive of STS. The dog was receiving carprofen once daily for chronic osteoarthritis and displayed hindlimb weakness.

Mass removal

The mass was noticeably larger when the dog returned for excision four days after the initial presentation (Figure 1). The dog was premedicated with acepromazine, butorphanol, carprofen, and maropitant. General anesthesia was induced with propofol and maintained with isoflurane.

The branches of the lateral saphenous vein were identified so as to be avoided. An elliptical incision was made over the lateral aspect of the mass using a surgical flexible hollow waveguide CO₂ laser (VetScalpel by Aesculight, Bothell, Wash.) set to 10 watts, in the continuous wave mode, and with an adjustable handpiece set to 0.25-mm focal spot size (Figure 2). The power setting was kept relatively low in this case because the skin in the area was thin. The grossly encapsulated mass was readily separated from the overlying dermis with a blunt instrument and laser dissection (Figure 3). The deep attachments were severed with laser dissection while placing traction on the mass measuring 4 x 5 x 2 cm (Figures 4 and 5). Saline-soaked gauze was used as a backstop. Visible remnants of the deep attachment were ablated with the power set to 6 watts continuous, the focal spot size adjusted to 0.4 mm, and laser tip-to-tissue distance increased to defocus the beam. Hemorrhage was well controlled with this technique.

The subcutaneous tissue was apposed with 4-0 polydioxanone in a continuous pattern and the skin closed with 3-0 polypropylene in a cruciate pattern (Figure 6). A modified Robert Jones bandage was placed on the leg. The dog was discharged the same day with instructions for confinement and limited activity. Oral carprofen was resumed the following day.

Outcome

Histopathology of the mass confirmed a Grade 1, moderately well-differentiated STS. Proliferative spindle cells extended to the margin of the submitted specimen, suggesting incomplete excision. However, the deepest aspects of the tumor were ablated with the laser in thin layers, so the full extent of the tumor excision was uncertain. The owner declined more aggressive surgery or referral to a veterinary oncologist for radiation therapy or chemotherapy.

The bandage was changed every two to three days for two weeks and the incision remained clean and dry. Sutures were removed after three weeks. Healing was uneventful, with minimal swelling or discomfort. Upon reexamination at three months (Figure 7) and four months postsurgery, the mass has not recurred.

The primary benefits of utilizing CO₂ laser surgery in this case were:

1. hemorrhage control
2. pinpoint ablation of grossly abnormal tissue, and
3. minimal postoperative pain or swelling.

Jon Plant, DVM, DACVD, was an early adopter of the flexible hollow waveguide CO₂ laser in veterinary medicine. After 15 years of dermatology referral practice in Southern California, he taught at the Oregon State University, College of Veterinary Medicine, served as a dermatology consultant for Banfield Pet Hospitals and Dechra, founded SkinVet Clinic (skinvetclinic.com) in Oregon, and developed RESPIT allergen immunotherapy. He is a graduate of Reed College and Oregon State University.

References

1. Elmslie RE, Glawe P, Dow SW. Metronomic therapy with cyclophosphamide and piroxicam effectively delays tumor recurrence in dogs with incompletely resected soft tissue sarcomas. J Vet Intern Med. 2008; 22:1373–1379.
2. Forrest LJ, Chun R, Adams WM, et al. Postoperative radiotherapy for canine soft tissue sarcoma. J Vet Intern Med. 2000; 14:578–582.
3. Kuntz CA, Dernell WS, Powers BE, et al. Prognostic factors for surgical treatment of soft-tissue sarcomas in dogs: 75 cases (1986–1996). J Am Vet Med Assoc. 1997; 211:1147–1151.
4. Stefanello D, Morello E, Roccabianca P, et al. Marginal excision of low-grade spindle cell sarcoma of canine extremities: 35 dogs (1996–2006). Vet Surg. 2008; 37:461–465.

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