Laryngeal hemiplegia is a prevalent upper respiratory dysfunction that limits the performance of large horses (2,3). Immobility of the arytenoid cartilage causes inspiratory obstruction. Horses with laryngeal hemiplegia show excessive inspiratory noise, hypercapnia, hypoxemia, and metabolic acidosis, leading to reduced athletic ability, although the etiology is not fully understood (5,7,12). In a previous report, of 375 horses with laryngeal paralysis, 94% had recurrent laryngeal neuropathy (3). The disease is characterized by degenerative changes in the recurrent laryngeal nerve, causing paralysis of the laryngeal abductor and cricoarytenoideus dorsalis muscles. Muscle paralysis results in immobility of the arytenoid cartilage and the vocal cords (5,7), causing a decrease in the diameter of the rima glottis; this condition is progressive and incurable (4).

Horses with this condition are usually surgically treated, preferably using laryngoplasty (7,10,15). The goal of treatment is to reduce respiratory noise and improve performance by increasing the diameter of the rima glottis, thereby increasing inspiratory flow. Arytenoidectomy can be applied for failed laryngoplasty (5,6,8,11); however, because total arytenoidectomy complications are fatal to patients (13), subtotal arytenoidectomy or partial arytenoidectomy is usually performed. Subtotal arytenoidectomy involves the removal of the arytenoid cartilage, leaving the corniculate process and the muscular process, while partial arytenoidectomy, which has better outcomes, leaves only the muscular process (5,8).

This case report describes a partial arytenoidectomy of a horse with laryngeal hemiplegia that was treated unsuccessfully with laryngoplasty.

A 3-year-old Thoroughbred gelding presented with left laryngeal hemiplegia and a history of failed prosthetic laryngoplasty (tie-back surgery); the horse underwent laryngoplasty 2-month ago and the failure was confirmed a month ago. Resting endoscopy revealed no abduction of the left arytenoid cartilage and no inflammatory changes in the larynx or surrounding structures (Fig. 1). Blood tests revealed no significant findings. Partial arytenoidectomy was chosen considering the failure of a previous prosthetic laryngoplasty.

Figure 1. Endoscopic view of the larynx. Resting endoscopy shows no abduction of the left arytenoids cartilage (arrow) and no inflammatory changes of the larynx. R, the right side.

The horse was sedated with detomidine hydrochloride (0.02 mg/kg IV Detomidine; Provet Veterinary Products) and butorphanol tartrate (0.02 mg/kg IV Butophan; Myoungmoon Pharm. Co., Ltd). Penicillin G (12,500 IU/kg IM PPS; Daesung Microbiological Lab. Co., Ltd) and flunixin meglumine (1.1 mg/kg IV, Fotis; Dong bang. Co., Ltd) were administered preoperatively. The horse was administered diazepam (0.03 mg/kg IV Diazepam. Inj; Samjin Pharm. Co., Ltd.) and ketamine hydrochloride (2 mg/kg IV Ketamine. Inj; Yuhan) for anesthesia induction and an orotracheal tube was intubated. General anesthesia was maintained with isoflurane (Ifran; Hana Pharm. Co., Ltd.) alongside 100% oxygen supply.

The horse was positioned in a dorsal recumbent position. Temporary tracheostomy was performed to secure the airway, and a 10-cm skin incision was made at two-thirds of the middle section of the neck. Paired muscles were separated using Metzenbaum scissors to expose the trachea. The annular ligament between the ring cartilages was removed partially (< 50% of the diameter of the trachea). As the orotracheal tube was extubated, a silicone tracheostomy tube was intubated at the tracheostomy site (Fig. 2). After an endoscope was placed through the left nostril to visualize the surgical area, laryngotomy was performed to approach the arytenoid cartilage ventrally. A skin incision was made from the keel of the thyroid cartilage to the cricoid cartilage in the midline of the larynx using a No. 10 scalpel blade. The ventral aspect of the larynx was exposed through blunt dissection of the paired muscles using Metzenbaum scissors. The cricothyroid ligament and cricoid cartilage were incised. Blood control was done using dry or diluted epinephrine-soaked gauze and suction. Through the incision site, Allis tissue forceps were used to grasp the ventral aspect of the left arytenoid cartilage. A No. 20 scalpel blade was used to cut the arytenoid cartilage and mucosa to separate the muscular process from the other part of the arytenoid cartilage (Fig. 3A). After cutting the arytenoid cartilage with a scalpel, Allis tissue forceps were used to retract the cartilage rostromedially to detach the surrounding muscle. The left arytenoid cartilage and accompanying mucosa were removed (Fig. 3A), while the muscular process remained intact. Metzenbaum scissors were used to trim the surgical area. The mucosal defects were unsutured. The tracheotomy and laryngotomy incision sites remained open (Fig. 4). In the recovery room, the stainless tracheostomy tube was replaced with a silicone tracheostomy tube after the horse started to breathe spontaneously. The horse had a smooth recovery.

Figure 2. Tracheostomy tube intubation in the mid-cervical area of the neck.

Figure 3. Endoscopic view of the larynx. (A) Endoscopic view of the larynx during partial arytenoidectomy. Allis forceps were used to retract the left arytenoid cartilage. (B) Endoscopic view of the larynx on postoperative day 1. Endoscopy shows redundant mucosa of the arytenoid cartilage and swollen tissues of the surgical site. (C-E) Endoscopic view of the larynx at postoperative day 12. Rongeur forceps were used to trim and remove the redundant mucosa of the corniculate process of the arytenoid cartilage (asterisk). (F) Endoscopic view of the larynx at 2 months postoperatively. R, the right side.

Figure 4. Stainless tracheostomy tube (lower) and laryngotomy site (upper).

The horse was administered penicillin G (12,500 IU/kg IM. once daily for 3 weeks), gentamicin sulfate (6.6 mg/kg IV once daily for 3 weeks, Samu gentamicin injection; Samu median Co., Ltd.), flunixin meglumine (1.1 mg/kg IV once daily for 3 weeks), dexamethasone sodium phosphate (2.2 mg/kg IM once daily for 4 days, Dexason; Handong Co., Ltd.), and famotidine (1.8 mg/kg PO once daily for 3 weeks, Famotidine tap; Korea Nelson Pharm Co. Ltd.). Dexamethasone sodium phosphate was tapered down daily and was discontinued on postoperative day 4. The incision area was cleaned with a gauze soaked in normal saline, before applying antibiotic ointment (Banepo ointment; Daehan Pharm Co. Ltd.). The horse was fed on the ground on postoperative day 1. A stainless tracheostomy tube was removed on postoperative day 3. The horse showed no complications such as dysphagia or dyspnea. On postoperative day 12, resting-endoscopy showed the remaining mucosa of the corniculate process and granulation tissue at the surgical site (Fig. 3C). Rongeur forceps were used to remove the remaining tissues through the previous incision site under sedation with detomidine hydrochloride (0.02 mg/kg IV) and butorphanol tartrate (0.02 mg/kg IV) (Fig. 3D, E). The horse was discharged 1 month postoperatively and, the owner reported that the surgical site had healed with no evidence of granulation tissue 2 months postoperatively (Fig. 3F). The horse returned to training and racing 3 and 7 months postoperatively, respectively.

This is the first case report of a partial arytenoidectomy in a horse in South Korea. In horses, partial arytenoidectomy is considered a viable option for laryngeal disorders such as laryngeal hemiplegia and arytenoid chondropathy. In previous reports, partial arytenoidectomy was found to restore the upper airway function close to normal (8) and showed a similar postoperative efficacy and return to race rate as that of prosthetic laryngoplasty (10,15). In the current case, the horse underwent partial arytenoidectomy, with no significant postoperative complications, and returned to training within 3 months postoperatively. This indicates that partial arytenoidectomy could be beneficial for horses with failed laryngoplasty.

Airway contamination is one of the most serious complications faced by clinicians. Clinical signs such as dysphagia and dyspnea have been described in horses after partial arytenoidectomy (6,13). Speirs reported that 36% of horses showed dysphagia after partial arytenoidectomy (13); however, horses showing severe dysphagia after partial arytenoidectomy have been reported less frequently in recent studies (1,6,8,10,15). Recently, Radcliffe, et al. (10) reported airway contamination in horses 3 months after partial arytenoidectomy and laryngoplasty; the apparent inflammatory changes in tracheobronchial fluid indicated that both surgeries caused airway contamination. In the current case, the horse was encouraged to eat on the ground, which may have assisted its return to racing without significant complications. Accordingly, feeding on the ground is necessary for horses undergoing partial arytenoidectomy to prevent airway contamination.

Mucosal closure during partial arytenoidectomy is technically challenging and time-consuming. In the present case, the mucosal defects remained unsutured and the horse underwent re-surgery due to redundant mucosa of the corniculate process and granulation tissue on postoperative day 12. However, the surgical site reportedly recovered well without granulation tissue 2 months after surgery, and the horse returned to racing within 7 months. A previous study showed that among 76 horses that underwent partial arytenoidectomy with mucosal closure, 13 (17%) underwent re-surgery for granulation tissue at the surgical site (9). Likewise, of 14 horses after partial arytenoidectomy without mucosal closure, 3 (21.4%) had granulation tissue at the surgical site (6). Although granulation tissue at the surgical site is presumed to be caused by dehiscence or suture, no exact cause has been reported. Moreover, Tulleners, et al. reported that the primary closure could not prevent swelling or granulation of the surgical site (14). Besides, horses that have undergone partial arytenoidectomy with or without mucosal closure reportedly have similar return to racing rates (1,9). Therefore, partial arytenoidectomy without mucosal closure may be beneficial for both clinicians and horses.

In this case, partial arytenoidectomy was performed in a horse with a history of failed laryngoplasty. The horse returned to racing 7 months after partial arytenoidectomy with no significant complications. This case suggests that partial arytenoidectomy could be useful in horses with a history of failed laryngoplasty.

The authors have no conflicting interests.