Thyroidectomy in Horses

Diseased thyroids can cause respiratory distress, limited head and neck movement, and unsightly lumps in affected horses’ throat areas. In such cases veterinarians usually remove the thyroid under general anesthesia, but researchers recently developed a thyroidectomy technique for use in standing horses with simple sedation and local anesthesia. The results, they say, are a win-win for everyone.

“Our technique minimizes risk to the patient, reduces costs to the client, and limits complications arising from the procedure,” said Marco Marcatili, DVM, PhD, MRCVS, of the University of Glasgow School of Veterinary Medicine’s Weipers Centre Equine Hospital, in Scotland, and Pool House Equine Clinic in Lichfield, U.K.

Specifically, the researchers noted a marked reduction in the risk of recurrent laryngeal nerve neuropathy (RLNN, also known as “roaring”) after standing thyroidectomy compared to traditional thyroidectomy with the horse lying down under general anesthesia.

Furthermore, as with other surgical interventions that can now be performed standing—including enucleation (eye removal), tear-duct surgery, fracture repair, medial patellar ligament splitting (to treat upward fixation of the patella), larynx surgery, and even some forms of colic surgery—the sedation and local anesthesia keep risks low compared to general anesthesia.

“Potentially fatal complications of general anesthesia are more common in horses than in small animals and humans,” Marcatili said.

Marcatili and colleagues performed standing thyroidectomy on 10 horses that had presented to their clinics with enlarged thyroids. The patients represented a variety of breeds, including ponies, Arabians, saddle horses, and a Clydesdale cross, and ranged in age from 7 to 26. Two of the horses had thyroid enlargement on both sides of the neck. The surgeons sedated the horses and used local anesthesia in the throat region to remove the thyroid masses. Horses remained on stall rest for 10 to 14 days post-surgery until the sutures could be removed.

The research team did not identify any serious complications during surgery, bleeding was minimal, and mass removal was complete, Marcatili said. None of the horses developed RLNN, compared to a rate of up to 50% in horses undergoing traditional thyroidectomy. Additionally, all the horses went back to or exceeded their previous level of exercise.

The reduced RLNN rate could be due to surgeons’ improved access to the affected structures in standing horses, he said. Or it might be because the structures fell into their natural position—an advantage researchers have also noted in other standing surgeries.

Despite these advantages, the standing surgery does have its limitations. “Performing this procedure under standing sedation still requires a team of experienced nursing staff and competent handlers, and the temperament of some horses may mean they are unsuitable candidates for standing procedures,” Marcatili said.

“The technique has been validated by the present study,” he continued. “We feel that the technique should be considered a treatment option for clinical cases, but as is the case for the procedure performed under general anesthesia, it should only be undertaken by a trained surgeon.”

The study, “Standing thyroidectomy in 10 horses,” was published in Veterinary Surgery.