Surgery

Standing Sedation Safe for Removing Melanomas

By Adam Marcus

Resection of melanomas, including large lesions, can be safely accomplished on standing horses under appropriate sedation, according to veterinary researchers in France who have been performing the procedure at their facility.

In a new paper, the researchers described the approach in 20 horses that underwent standing resection of large melanomas. The researchers reported their findings in Veterinary Surgery and presented them at the 2023 annual congress of the French Equine Veterinary Association.

“I believe most equine surgeons could perform this technique of excision of extensive perianal melanomas,” said Mickaël P. Robert, MSc, DECVS, an equine surgeon at the Center Hospitalier Vétérinaire Equin de Livet, in Livarot-Pays-d’Auge, who led the study. “A good knowledge of the local anatomy is of course a prerequisite. Having a diode laser unit is probably beneficial for hemostasis, but not mandatory.”

Melanoma is the second most common form of cancer in horses, behind sarcoids, accounting for as many as 15% of malignancies in the species. Gray animals are particularly vulnerable to the disease; estimates suggest up to 80% of gray horses may develop melanocytic tumors.

Conventional treatment for melanomas in horses has involved the use of chemotherapeutic agents. Surgery has been considered too complicated, ineffective and possibly even responsible for promoting metastasis. However, as the latest article indicates, the operative approach has a high rate of success and a moderate risk for complications.

The 20 horses (median age, 15 years) in the study underwent resection of tumors at least 4 cm with standing sedation and epidural anesthesia. In 14 animals, surgeons were able to fully resect the anal margin of the tumors; deep perirectal dissection of the masses was required in 16 cases. Horses spent a median of 6.5 days in the hospital.

In terms of safety, 8 horses required additional injections of local anesthetic, and 1 animal experienced profuse bleeding during and after surgery, which required additional measures to control, Dr. Robert’s group reported.

One horse exhibited signs of colic in the hospital during recovery, while 10 other animals required manual evacuation of the rectum to facilitate fecal output.

After discharge, 4 horses developed mild signs of colic and 3 experienced problems with wound healing, 1 with partial dehiscence and 2 with hypergranulation. The rest of the animals recovered without incident within 12 weeks (1 animal that did poorly during surgery was euthanized after developing ataxia).

Six of the horses developed new melanomas, 1 of which appeared in the perianal region, over a median follow-up period of nearly 1 year, according to the researchers.

“We follow most of the horses in the article regularly,” Dr. Robert said. “So far we cannot prevent the development of new melanomas, we can only treat the preexisting ones and the ones that will appear at a later stage.”

Dr. Robert said equine veterinarians should consider the standing approach for horses with perianal melanomas, “especially if the masses are believed to grow quickly, if the horse is young, if the masses are infected or necrotic, if the horse displays functional deficits, or just to prevent additional complications.”

He and his colleagues have had success using the technique in animals with smaller lesions, too. “The procedure is then much easier, faster, less invasive and, of course less painful in the postoperative period. When the melanomas are reaching big sizes, like in our article, this technique is then probably the only solution to improve these horses’ comfort, and basically to allow them to pass feces in a normal way without obstruction.” MeV

Related: Should Horses Be Fasted Before Elective Procedures? looks at research on feeding hay before and after anesthesia.

For more information:
Robert MP, Buyck C, Tricaud C, et al. Radical surgical excision of extensive perianal melanomas on standing horses: Twenty cases. Vet Surg. 2024 Nov 20. doi: 10.1111/vsu.14192. Online ahead of print. https://onlinelibrary.wiley.com/doi/abs/10.1111/vsu.14192