Medical Treatment of Arytenoid Chondrosis
Acute inflammation associated with an arytenoid chondrosis can be treated aggressively with intravenous (IV) antimicrobials and antiinflammatory drugs, and may not require surgical intervention. Because it is difficult to get a bacterial culture to direct treatment, broad-spectrum antimicrobials are used. Potassium penicillin (22,000 IU/kg q6h), gentamicin (6.6 mg/kg q24h), phenylbutazone (4.4 mg/kg q12h), and dexamethasone (0.025-0.05 mg/kg q24h) are given intravenously. Because respiratory distress can be induced with any excitement, the horse should be kept in a quiet environment and monitored closely. An emergency tracheotomy kit should be kept stallside. Tracheotomy is reserved for situations in which the animal cannot be maintained in a quiet environment or when respiratory stridor is evident even when the animal is relaxed.
Within a few days dramatic improvement usually occurs with a decrease in the soft tissue swelling. Surgery is still not recommended at this point because many horses will continue to improve for 30 days with further rest and antimicrobial treatment. Horses are discharged with recommendations for oral antimicrobial treatment and 30 days of rest before endoscopic reevaluation to assess the need for further treatment. Horses that do not show dramatic improvement within the first few days on IV antimicrobial treatment, have gross purulent material draining from their arytenoid, or have swelling of the laryngeal saccule are taken to surgery more quickly. Swelling of the saccule indicates accumulation of purulent material abaxial to the arytenoid.
Further treatment is often predicated on the response to medical treatment and the proposed use of the horse. Several horses have gone back to racing after medical treatment alone despite having slightly abnormal looking corniculate processes of their arytenoids. These horses maintain good arytenoid abduction bilaterally. Those horses that have granulation tissue remaining on their arytenoid are best treated by laser excision of the tissue and rest. Several weeks are required for the mucosa to cover the defect before exercise can be resumed. If laryngeal function is still compromised sufficiently to compromise the horse’s athletic purpose, a partial arytenoidec-tomy should be considered. If the horse is intended to return to athletic performance, the clinician should ensure that one arytenoid has full function. If not it is unlikely an arytenoidectomy will be enough to return the horse to full athletic function.
Surgical Treatment of Arytenoid Chondrosis
A temporary tracheotomy must be performed so that the horse can be given anesthetic gas during the surgical procedure of partial arytenoidectomy. If too much laryngeal compromise exists initially, the tracheotomy should be performed with the horse standing to guarantee the horse a patent airway during induction of anesthesia. If a large enough lumen is present that an endotracheal tube can be passed through the larynx after anesthesia is induced, the tracheotomy is performed with the horse under general anesthesia and the endotracheal tube switched to the tracheotomy site once the horse has been anesthetized. This method will allow for a cleaner, smaller tracheotomy. Caution should be exercised so the tracheotomy site is not placed too far cranially. The position of the tracheotomy relative to that of the larynx is deceptive when the horse is under anesthesia and the head extended. If the tracheotomy is placed too far cranially it may become obstructed during recovery from anesthesia.
To perform an arytenoidectomy a standard laryngotomy approach is first made to the larynx. A headlamp is very useful for illumination while the clinician is working within the larynx. Placement of the endoscope through the nares in front of the larynx can also supplement light. Multiple techniques exist for performing partial arytenoidectomy. It is always best to try and salvage a mucosal flap on the axial side of the arytenoid to achieve primary mucosal closure after the arytenoid is removed to minimize the prospect of granulation tissue formation postoperatively. Before performing the arytenoidectomy, the clinician should remove the vocal chord and ventricle. This procedure leaves an opening at the ventral aspect of the arytenoidectomy site for any drainage of submucosal hemorrhage or clot abaxial to the final mucosal flap.
To form the mucosal flap, mucosal incisions are made from dorsal to ventral at the caudal border of the arytenoid and the rostral border, just caudal to the corniculate. These incisions are connected in a horizontal incision along the ventral border of the arytenoid. The mucosa is slowly dissected free from the arytenoid and left attached dorsally. The abaxial border of the arytenoid is then freed of its muscular attachments with primarily blunt dissection to minimize hemorrhage. The muscular process is isolated and transected. The clinician then elevates the arytenoid and frees it completely by cutting the remaining corniculate mucosa rostrally. Any remaining dorsal attachments are also cut and the cricoarytenoid joint capsule is cut caudally. Mucosa is held together to plan closure, and excess mucosa is trimmed. The caudal edge of the mucosal flap is apposed to the laryngeal mucosa in a simple continuous pattern with absorbable suture, with the clinician working dorsal to ventral. The rostral edge of the mucosal flap is apposed similarly to the remaining mucosa that was abaxial to the corniculate, in a parallel line to the caudal edge. The most difficult part of the incision is its very dorsal aspect; it is extremely important to close the dorsal aspect to prevent the formation of granulation tissue. The ventral aspect is left open to drain. Bleeding should be minimal once the mucosal edges are apposed. Any granulating “kissing” lesions on the opposite arytenoid should be debrided at this time. If extensive purulent material exists abaxial to the arytenoid, a mucosal closure is not performed. At the conclusion of surgery the endotracheal tube can be replaced with an equivalent size tracheotomy tube for the horse’s recovery from general anesthesia.
On the morning after surgery another endoscopic examination should be performed. A clear opening to the glottis should exist; if the clinician holds off the tracheotomy tube while watching the horse’s respiratory effort, laryngeal function can be assessed. If laryngeal function is adequate for the horse to breathe easily through its nares, the tracheotomy tube can be removed. The horse should be maintained on perioperative antimicrobials and antiinflammatories for 1 week while being maintained in a stall for 1 month. During this time, the horse can be allowed to graze under hand restraint. The tracheotomy and laryngotomy sites are left open to heal in by second intention. All feeding should take place from the ground to minimize the risk of aspiration. An endoscopic examination should be performed 1 month postoperatively to determine the presence of granulation tissue. Once mucosal healing is complete the horse should receive a 1-month turnout before resuming exercise.
Several potential complications of this surgery exist. The most common complications after an arytenoidectomy are granulation tissue or excessive residual mucosa. The clinician should remove this substance at the first month by videoendoscopic laser excision performed with the horse standing under sedation. If it is not removed in the early stages, the tissue may mineralize and make excision much more difficult later. A more serious, life-threatening complication is aspiration pneumonia. The risk of pneumonia may be dramatically decreased by less traumatic dissection of the arytenoid from the lateral musculature at the time of surgery. Many of these muscle bellies narrow the glottis while the horse swallows, thus playing a protective role. Another complication is postoperative noise. This postoperative respiratory noise most likely originates from vibration of the residual arytenoid/corniculate mucosa. An examination performed with the horse on a treadmill may be beneficial to make this determination. The adjacent aryepiglottic fold that is no longer held abaxially by the arytenoid can be the offending soft tissue that obstructs the airway. This tissue, or any residual arytenoid mucosa, can be identified during an endoscopic examination performed while the horse is exercising on a high-speed treadmill. The tissue should be removed as needed.