CO₂ laser excision of a CHP

By María Suárez, DVM, PhD, CVA and Anya Glazkova, PhD. For The Education Center

Originally published in Veterinary Practice News, February 2015 – Download as a PDF

Canine hemangiopericytoma (CHP) is a malignant neoplasm found in cutaneous and subcutaneous tissues. Histologically, CHP is characterized by perivascular formation of spindle-shaped cells arranged in distinctive whorl patterns.^[1,2]

These tumors are most common in extremities, although other locations have also been reported. CHP usually affects middle-aged and older dogs, and large breeds appear to be more prone.^[2] Differential diagnosis includes cutaneous fibrous histiocytomas, schwannomas, fibrosarcomas and other spindle cell tumors.^[1]

Typically, the treatment for CHP is an excision with wide and deep safety margins. Occasionally, more radical surgery, such as limb amputation, is required. However, because the necessary margin extent is commonly underestimated, tumors tend to recur (with a 26 percent to 60 percent rate) and re-growth is typically more aggressive.^[1]

Factors that affect the possibility of complete excision include the surgeon’s skill; histological grade; and the tumor’s infiltrative nature, size and location. The surgical modality (scalpel, electrosurgery or laser) can also influence the outcome of the tumor removal.

For the CHP case described in this article, we used our Aesculight surgical CO₂ laser. CO₂ laser surgery has become a well established treatment modality in veterinary medicine.^[3] The laser’s wavelength of 10,600 nm is very well absorbed by water, its main chromophore. This unique wavelength allows for efficient cutting, ablation and coagulation of soft tissue, which is rich with water.

Moreover, the laser is an excellent coagulator—it achieves hemostasis by coagulating small (sub 0.5 mm) blood and lymphatic vessels. This translates into better visualization and higher precision of tissue cutting and removal.^[4,5] In addition, sealed lymphatics ensure less swelling post-operatively.

Clinical literature suggests that sealing blood and lymphatic vessels with laser energy can help to prevent the spreading of tumor cells.^[5,6] Holt and Mann^[6(p.581)] indicate that the non-contact operating mode of the CO₂ laser, along with its unique ability to create a “vaporized barrier” between the excised tumor and the tumor bed, reduces the intraoperative wound contamination by tumor cells. The laser also seals nerve endings, which ensures less pain and a more comfortable recovery for the patient.^[5]

The laser-tissue interaction and the degree of thermal necrosis are well controlled through use of proper laser settings, such as power density, continuous wave or pulsed mode, pulse durations and exposure times. The zone of thermal damage may be as small as 50 μm thick.^[2] Also, the non-contact cutting/ablation ensures no mechanical trauma to the tissue.

Case

Chiko, a 9-year-old intact male Ibizan dog, was presented with a 1.1 cm tumor on the left forelimb. The tumor appeared as a raised, poorly demarcated, painless mass. The referring veterinarian had removed a tumor at the same site 18 months earlier with a scalpel. Pathology of the initial specimen indicated a low to intermediate grade soft tissue sarcoma. No other treatments were done after the first surgery.

The fine needle aspirate biopsy results appeared to suggest fibrosarcoma. The owners did not want to have the limb amputated. It was decided to use the CO₂ laser both for its surgical advantages and for the possibility of tissue ablation in palliative procedures.

It should be noted that the histopathological analysis of the laser-excised tumor specimen ruled out our initial diagnosis of fibrosarcoma, and the definitive diagnosis of hemangiopericytoma was made.

Anesthesia

The patient was pre-medicated with medetomidine 0.005 mg/kg IM, methadone 0.3mg/kg IM, carprofen 2 mg/kg IM. Induction with propofol. General anesthesia maintained with isofluorane via endotracheal tube.

Laser Equipment

Thirty-watt Aesculight surgical CO₂ laser with a flexible hollow waveguide and tipless adjustable handpiece (shown in Figures 1, 3, 6 and 7)

LASER SETTINGS

Incision:	Resection:	Tumor bed ablation:
Spot size: 0.4 mm Power: 12 watts Laser mode: continuous wave (CW)	Spot size: 0.4 mm Power: 8-10 watts Laser mode: CW	Spot size: 1.4 mm Power: 4 watts Laser mode: CW

Technique

To ensure complete removal of all malignant cells, the initial surgical incision included the safety margins of apparently healthy tissue—1 cm laterally and distally and 2 cm proximally from the mass (see Figure 1). The laser handpiece was held perpendicular to the target tissue (shown in Figures 1, 3, 6 and 7). Once adequate edges were produced, traction tension was applied to the tumor to facilitate cutting.

The laser settings were changed to 8-10 watts of continuous wave for dissection. The laser provided good coagulation for smaller blood and lymphatic vessels, but larger blood vessels had to be carefully clamped and ligated (Figure 2). Between laser passes, any char was removed with a sterile saline-soaked gauze pad to avoid unnecessary thermal damage.

In the course of the procedure, we discovered that the tumor had infiltrated between the tendons (Figure 4), and had almost reached the dorsal part of the limb all the way from the palmar surface. The laser facilitated the dissection by decreasing the bleeding, which is typically quite severe in this area and is exacerbated by the tumor.

Dissection was performed meticulously around flexor tendons to free them from the infiltrating mass without damage (Figure 8). Tendons and ligaments are poorly vascularized and their healing can be challenging if the blood supply is compromised.

Unfortunately, the tumor had infiltrated underneath the distal pad as well, and complete excision could not be expected without limb amputation. Therefore, we ablated the tumor bed by using the 4 watt CW laser setting with the largest laser beam spot size of 1.4 mm. The adjustable handpiece made changing the spot size very quick.

Wound Closure and Dressing

The amount of tissue excised with the tumor was too significant to allow for suturing. The sutures were only placed at the 12 and 6 o’clock positions to avoid tension and distal compression (Figure 10). The surgical dressing was placed to protect the wound and promote healing. A sterile hydrogel, Askina Gel, was applied as an abundant contact layer, which allowed for the optimal level of hydration at the wound site. This not only facilitated the granulation process but also prevented the drying of tendons. The potential risks of drying are tendon retraction and infection.

Comments

We decided not to perform a skin graft for two main reasons: at first, there was not enough tissue to support the graft (tendons stripped of their overlying connective tissue do not provide a satisfactory skin graft support)^[7]; and by the time enough tissue formed to support the graft, Chiko had been recovering so well that we decided to spare him unnecessary pain and the risks of general anesthesia.

Post-Operative Care

The patient was released from the clinic 24 hours after the procedure with the medical dressing (Askina Gel covered with sterile cotton gauze held with a cohesive bandage). The dressing was changed twice a week. The owners were instructed to give the dog antibiotics (amoxicillin/clavulcanic acid 15 mg/kg) twice a day for the first three weeks following the surgery. They were advised to make sure Chiko did not disturb the bandages or re-injure himself. This did not turn out to be an issue and no e-collar was required.

Follow-Up Exams

He was brought in for follow-up examinations at four days post-operatively (Figure 11), then twice a week for the next seven weeks. The owners were very apprehensive and did not want to see or manipulate the wound at home and preferred to visit the hospital instead (Figures 12-15).

The follow-up examinations showed that there was no tendon retraction or loss of ROM in the carpus. The patient was leading a normal life and did not disturb or even pay attention to the bandages. The 5.5 week post-operative visit showed that the wound was completely filled with only 2 x 1 cm area left to epithelialize (Figure 15). At eight weeks after the surgery, the site healed completely (Figure 16).

We will perform re-checks every 3 months to monitor the surgical site. Chiko was prescribed metronomic chemotherapy, starting week seven after the surgery. Since the tumor was infiltrating and aggressive, and no clean margins could be obtained, we expect recurrence. This could have happened as soon as two months after the surgery (but it has not happened) and is very likely in less than a year.

Conclusions

Our laser enabled us to excise the tumor with maximum accuracy. Due to its hemostatic ability it provided excellent visibility of the operating site. The bactericidal properties of the laser and the non-contact cutting/ablation allowed us to avoid post-operative inflammation or infection.

The patient was fully weight bearing and appeared to be pain free since Day One after the surgery. He has shown good recovery and the wound has healed nicely. The pet owners are very happy with the outcome and the course of recovery, and are grateful that the CO₂ laser surgery enabled us to avoid the limb amputation, at least for now. We have been monitoring the patient regularly and will continue to see him every three months.

4 1/2 month checkup

References

1. Pérez J, Bautista MJ, Rollón E, de Lara FC, Carrasco L, Martin de las Mulas J. Immunohistochemical characterization of hemangiopericytomas and other spindle cell tumors in the dog. Vet Pathol. 1996;33(4):391-7.
2. Connery NA, Bellenger CR. Surgical management of haemangiopericytoma involving the biceps femoris muscle in four dogs. J Small Anim Pract. 2002;43(11):497-500.
3. Palmer SE. Treatment of common cutaneous tumors using the carbon dioxide laser. Clin Tech in Equine Pract. 2002;1(1):43-50.
4. Wilder-Smith P, Arrastia A-M, Liaw L-H, Berns M: Incision properties and thermal effects of three CO₂ lasers in soft tissue. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1995;79:685–91.
5. Berger N, Eeg PH. Veterinary laser surgery a practical guide. Iowa: Blackwell Publishing, 2006.
6. Holt TL, Mann FA. Soft tissue application of lasers. Vet Clin Small Anim. 2002;32:569–99.
7. Hedlund CS. Surgery of the integumentary system. In: Fossum TW, ed. Small animal surgery, 3rd ed, St. Louis, MO: Elseveir/Mosby, 2007;159-259.

Acknowledgements: The authors thank UCM students, residents and especially Dr. Pedro Urrutia and Dr. Olga García Sastre for the clinical photographs of the case.

María Suárez, DVM, Ph.D., CVA, works as a small animal surgeon and clinical instructor at the Veterinary Teaching Hospital of the Complutense University in Madrid, Spain. She is a partner in an integrative medicine practice, Integra CV, in Majadahonda in Madrid. Dr. Suárez works with both surgical CO₂ and therapeutic lasers daily.

Anya Glazkova, Ph.D., is a recent graduate of the University of Washington in Seattle. She helps conduct laser surgery educational programs at Aesculight and LightScalpel LLC.

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