Roarers - surgery for recurrent laryngeal neuropathy -impact and outcomes

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ROARERS - surgery for recurrent laryngeal neuropathy – impact and outcomes Safia Barakzai BVSc MSc DESTS Dipl.ECVS  Recurrent laryngeal neuropathy (RLN), more commonly known as ‘roaring’, ‘laryngeal paralysis’ and ‘laryngeal hemiplegia’ is a disorder affecting primarily the left recurrent laryngeal nerve in horses >15hh. This nerve supplies the muscles that open and close the left side of the larynx. The right recurrent laryngeal nerve is also now proven to be affected, but only very mildly, thus affected horses very rarely show signs of right-sided dysfunction.   Horses with RLN become unable to fully open (abduct) the left side of their larynx. During exercise they then make abnormal inspiratory noise due to collapse of both the vocal fold(s) and the left arytenoid cartilage (figure 1), and airflow to the lungs can become severely obstructed in advanced cases. There is a proven genetic component to RLN, but in many cases the disease progresses over months or years. The age at which clinical signs become apparent is highly variable. Foals can show endoscopic and pathologic evidence of RLN, but some horses do not develop clinical disease until >10 years old.  Severity of disease can be reasonably estimated using endoscopy in the resting horse (grades 1-4), but the gold standard for assessing this disease is endoscopy during exercise, when the high negative pressure—generated when breathing—test the affected laryngeal muscle, which is trying its best to resist the ‘suction’ effect of inspiration (Fig. 1). During exercise, RLN is graded from A to D, depending on how much the left side of the larynx can open (Table 1).   Figure 1: Horse undergoing exercising endoscopy to ascertain how the left arytenoid performs when the airway is under pressure. Inset photos show resting (top) and then exercising endoscopy (bottom) of a larynx with grade D arytenoid collapse (green arrow) with additional deformation of the arytenoid cartilage shape and bilateral vocal fold collapse (red arrows). Laryngeal grade at exerciseDefinitionAppearance of larynx endoscopicallyAFull abduction of the arytenoid cartilages during inspiration BPartial abduction of the affected arytenoid cartilages (between full and the resting position) CAbduction held at the resting position DCollapse into the contralateral half of the rima glottidis during inspiration Table 1: Grades A-D of laryngeal abduction during exercise. Figures c/o F. Rossignol. Treatment of RLNTraditionally, left-sided ventriculocordectomy (‘Hobday’/ventriculectomy plus vocal-cordectomy surgery) and laryngoplasty (‘tie-back’) surgeries have been used to treat the disorder, depending on which structures are collapsing and how severely. The intended use of the horse, the budget available and other concerns of the owner/trainer also come into play. New techniques of providing a new nerve supply (‘re-innervating’) to the affected muscle are now being trialled in clinical cases. Pacing the muscle with an implanted electronic device has also been attempted in research cases.   VentriculocordectomyVentriculocordectomy is commonly now referred to as a ‘Hobday’ operation; however, the ‘Hobday’ actually only refers to removal of the blind ending sac that constitutes the laryngeal ventricle. Currently, surgeons tend to remove the vocal cord as well as the ventricle, because it is vocal cord collapse that creates the ‘whistling’ noise. It is a relatively straightforward surgery to perform with minimal risks and complications for the patient. In the last 15 years, there has been a shift to performing it in a minimally invasive way, using a diode laser under endoscopic guidance in the standing sedated horse rather than with the conventional method, via an open laryngotomy incision on the underside of the neck with the horse under a general anaesthetic. However, transendoscopic laser surgery is technically difficult with a very steep learning curve for the surgeon. All ventriculocordectomies are not equal (Fig. 2) and for both laser and ‘open surgery’ methods, incomplete resection of the fold can leave behind enough tissue to cause ongoing respiratory noise and/or airway obstruction after surgery.1,2,3   Figure 2: Two horses after ventriculocordectomy surgery. The horse on the left has an excellent left-sided ventriculocordectomy, with complete excision of the vocal fold tissue (black arrow). The right cord is intact, but the right ventricle has been removed (‘Hobday’). The horse on the right has bilaterally incomplete vocalcordectomies, with much of the vocal fold tissue left behind (green arrows).    Sports horses, hunters and other non-racehorses were often previously recommended to have a ventriculocordectomy performed rather than a laryngoplasty, even if they had severe RLN. This decision was often made on the grounds of cost, but also due to fear of complications associated with laryngoplasty (‘tie-back’ surgery). A new study has shown that for horses with severe RLN, a unilateral ventriculocordectomy is actually extremely unlikely to eliminate abnormal noise in severely affected horses, because the left arytenoid cartilage continues to collapse.3  The authors recommended that laryngoplasty plus ventriculocordectomy is a better option than ventriculocordectomy alone for all grade C and D horses if resolution of abnormal respiratory noise and significant improvement of the cross sectional area of the larynx are the aims of surgery.3   Advancements in laryngoplasty (‘tie-back’) surgery Laryngoplasty is indeed one of the most difficult procedures that equine surgeons perform,  and suffice to say that with such an advanced surgery, using a registered specialist veterinary surgeon that has considerable experience in airway surgery will likely minimise the chances of a negative outcome. Laryngoplasty surgery has an unjustified poor reputation in my opinion, but major improvements have occurred in the last few years. The persistently coughing horse with regurgitation of food from its nostrils after laryngoplasty should be a thing of the past. Refinements to the surgical technique of laryngoplasty, better knowledge of the anatomy around the arytenoid cartilage and new surgical methods to deal with dysphagic horses (coughing/nasal discharge) after laryngoplasty surgery all contribute to this.   Laryngoplasty was traditionally performed under general anaesthesia, however Rossignol et al. 4 first described the technique in standing sedated horses in 2015, and most upper airway surgeons now perform laryngoplasty with the horse standing (Fig. 3), as long as the patient is amenable. Results in standing cases have been equivalent to those performed under general anaesthesia.4  Figure 3: Laryngoplasty (tie-back) being performed in standing sedated horses.  Complications after laryngoplastyGradual loss of surgical abduction (opening) of the larynx occurs in 100% of cases to some degree after laryngoplasty. The average post-operative long-term loss of abduction is 1 grade1,2 (out of 5 grades), and this degree does not significantly affect the long-term result. However, in some cases, more profound abductory loss does occur. Although a wider degree of abduction logically creates a larger cross section of the airway, it has been shown that in UK National Hunt horses, there is no significant difference in racing performance of horses that had moderate (Grade 3 of 5) post-operative abduction compared to those with wide (Grades 1 and 2) abduction.5 It would appear that providing stability to the left arytenoid cartilage is the most important factor in removing respiratory noise and improving airway function, and not simply the degree of abduction present.   In the majority of horses, respiratory noise during exercise is significantly improved after surgery, but some ongoing respiratory noise is not uncommon. Until recently, noise was often blamed on ‘failure’ of the tieback surgery. However, the first papers1,2,6 showing results of exercising endoscopy in horses after laryngoplasty have been eye opening and indicate that other noise-causing abnormalities are often present in horses after laryngoplasty.  These include right vocal fold collapse, soft palate issues and ary-epiglottic fold collapse.  True surgical failure (i.e., an unstable and non-abducted cartilage) is definitely associated with noise but is fairly rare. The conclusion of these three studies was that a) exercising endoscopy is absolutely key to investigate such cases and b) in many cases, post-operative noise can be improved further with a relatively simple standing surgery rather than having to repeat the tie-back. Preliminary results of an ongoing study funded by the Horserace Betting Levy Board correlating sound recordings of horses after laryngoplasty with grade of abduction after laryngoplasty shore up these findings.7    Dysphagia (difficulty swallowing food) and coughing are uncommon after laryngoplasty, but occasionally horses can be severely affected; and the cough becomes so bad that it does affect the horse’s quality of life (approx. 3.5% of cases).8  In mild cases that only cough during exercise, withholding feed from horses for several hours prior to exercise can be a simple way to successfully manage them. In the past, the only way to manage a severely coughing horse after laryngoplasty was to surgically remove the sutures that hold the larynx open.  This should be left as long as possible after the initial surgery to allow adhesions to form and keep the abducted arytenoid in an open position. Suture removal is reported to fully resolve coughing in two thirds of cases.8 Once the suture is removed, 50% of cases will experience significant loss of abduction of the left arytenoid cartilage8 (i.e., any benefit of the laryngoplasty may be lost). A new alternative to suture removal is to surgically section any adhesions that have formed around the suture which may have ‘adhered’ the cranial oesophageal diverticulum to the other tissues around the suture, causing distortion of this top part of the oesphagus. Because the suture is not removed, the left arytenoid stays in the open position. This method certainly does relieve clinical signs of coughing in some cases, but it is not known yet whether this is a useful long-term resolution or whether new adhesions will form over time. The simple recent anatomic description of the cranial oesophageal diverticulum9 is probably the most groundbreaking revelation, which has decreased the incidence of post-operative coughing after tie-back surgery. With surgeon education about the anatomy of the upper oesophageal diverticulum, it is easy to avoid this structure and thus drastically reduce risks of both post-operative dysphagia/coughing and surgical site infection. Another new and exciting minimally invasive solution for horses that cough after laryngoplasty has also recently been described by Professor Ducharme from Cornell University. It is suitable for horses that have a ventral glottic defect (i.e., the left and right arytenoids meet during a swallow), but food may enter the trachea through the gap where the vocal cordectomy(ies) has been performed. The procedure involves bulking of this area with a solid ‘filler’ material, injected under endoscopic guidance, and has shown very promising outcomes in the first cases. Results have not been published at the present time.   Treatments that restore function of the weakened laryngeal muscleSeveral research groups  are searching for a more physiologic method of restoring function of the muscle that controls laryngeal opening (crico-arytenoideus dorsalis muscle, or CAD). In the past, grafts consisting of a piece of strap muscle, and the nerve that supplies it has been implanted in the affected CAD.10 This technique works well in theory but is very technically challenging, and it seemed that only a few surgeons worldwide had success with it. Using an electronic pacemaker implanted in the horse’s neck (functional electrical stimulation, or FES) to stimulate the abductor branch of the recurrent laryngeal nerve has been shown to be successful in small numbers of experimental cases.11-13 There appear to be unresolved issues with high cost and with keeping the electrodes in place. For racehorses, the pacer could potentially be interfered with externally and used to manipulate racing performance, thus approval from regulatory bodies seems unlikely. These factors have prevented these implants being used in clinical cases, in the UK at least.   Direct re-innervation of the diseased CAD muscle with a cervical nerve implant14 has shown good preliminary results in clinical cases, particularly those with less severe RLN. When re-innervation and electrical pacing are combined, results are thought to be more reliable (J Perkins personal communication), and this is probably the best bet for the future. As for any novel surgical technique, questions still remain for the success rate of re-innervation procedures, including the degree of abduction that can be obtained (usually only partial abduction is achieved) and the loss of muscle mass is likely to occur when the horse is rested for any period of time, because higher speed exercise is required to ‘pace’ the cervical nerve.   In summary, our assessment and understanding of current treatments for RLN is ongoing. Refinements to surgeries, including understanding why complications/failures occur and how best to treat them are evolving fast. In the near future, more functional treatments will hopefully become more affordable and available, but like all new surgical techniques, long-term results in large numbers of clinical cases need to be evaluated before the true ‘success’ rate is known.  ReferencesDavidson, E.J., Martin, B.B., Rieger, R.H., Parente E.J. (2009)  Exercising videoendoscopic evaluation of 45 horses with respiratory noise and/or poor performance after laryngoplasty. Vet. Surg 39, 942-948.Barnett, T.P., Dixon, P.M., Parkin, T.D.H. and Barakzai, S.Z. (2011) Long-term exercising video-endoscopic examination of the upper airway following laryngoplasty surgery: A prospective cross-sectional study of 41 horses. Equine Vet J. 45,,593Barakzai S.Z., Wells, J., Parkin, T. Cramp, P. (2019) Overground endoscopic findings and respiratory sound analysis in horses with recurrent laryngeal neuropathy after unilateral laser ventriculocordectomy. Equine Vet J. 51, 185-191 Rossignol F, Vitte A, Boening J, Maher M, Lechartier A, Brandenberger O, Martin-Flores M, Lang H, Walker W, Ducharme N. (2015) Laryngoplasty in standing horses Vet Surg 44 341-347 Barakzai, S.Z., Boden, L.A. and Dixon, P.M. (2009b) Postoperative race performance is not correlated with degree of surgical abduction after laryngoplasty in National Hunt Thoroughbred racehorses. Vet. Surg. 38, 934-940. Leutton, J.L. and Lumsden, J.M. (2015) Dynamic respiratory endoscopic findings pre and post-laryngoplasty in Thoroughbreds. Equine vet. J. 47, 531-6Barakzai S.Z., Parkin, T. Cramp, P. Ongoing HBLB research study.  Correlation of arytenoid abduction and other exercising endoscopic findings with respiratory noise in horses after laryngoplasty.   Fitzharris LE, Lane JG, Allen KJ. (2019) Outcomes of horses treated with removal of a laryngoplasty prosthesis. Veterinary Surgery. 48, 465-72. Brandenberger O, Pamela H, Robert C, Martens A, Vlaminck L, Wiemer P, Barankova K, Van Bergen T, Brunsting J, Ducharme N, Rossignol F (2016) Anatomical description of the boundary of the proximal equine esophagus and its surgical implications on prosthetic laryngoplasty in horses. Veterinary Surgery 45:6 E1-E22. Fulton, I.C., Anderson, B.A., Stick, J.A., Robertson, J.T. (2012). Larynx. In: Equine Surgery. Eds. Auer, J. and Stick, J.A. Pub. Elservier, St Louis, Missouri. Pp 592-623.Ducharme NG, Cheetham J, Sanders I, Hermanson JW, Hackett RP, Soderholm LV, Mitchell LM. (2010) Considerations for pacing of the cricoarytenoid dorsalis muscle by neuroprosthesis in horses. Equine Vet J. 42(6):534-40. Cheetham J, Perkins JD, Jarvis JC, Cercone M, Maw M, Hermanson JW, Mitchell LM, Piercy RJ, Ducharme NG. (2015) Effects of Functional Electrical Stimulation on Denervated Laryngeal Muscle in a Large Animal Model. Artif Organs. 39:876-85. Cheetham J, Regner A, Jarvis JC, Priest D, Sanders I, Soderholm LV, Mitchell LM, Ducharme NG. (2011) Functional electrical stimulation of intrinsic laryngeal muscles under varying loads in exercising horses. PLoS One. 2011;6(8):e24258. doi: 10.1371/journal.pone.0024258. Rossignol F, Brandenberger O, Perkins JD, Marie JP, Mespoulhès-Rivière C, Ducharme NG. (2018) Modified first or second cervical nerve transplantation technique for the treatment of recurrent laryngeal neuropathy in horses. Equine Vet J.  50,457-464. 

By Safia Barakzai

Recurrent laryngeal neuropathy (RLN), more commonly known as “roaring”, “laryngeal paralysis” and “laryngeal hemiplegia” is a disorder affecting primarily the left recurrent laryngeal nerve in horses >15hh. This nerve supplies the muscles that open and close the left side of the larynx. The right recurrent laryngeal nerve is also now proven to be affected, but only very mildly, thus affected horses very rarely show signs of right-sided dysfunction. Horses with RLN become unable to fully open (abduct) the left side of their larynx. During exercise they then make abnormal inspiratory noise due to collapse of both the vocal fold(s) and the left arytenoid cartilage (Fig. 1), and airflow to the lungs can become severely obstructed in advanced cases. There is a proven genetic component to RLN, but in many cases the disease progresses over months or years. The age at which clinical signs become apparent is highly variable. Foals can show endoscopic and pathologic evidence of RLN, but some horses do not develop clinical disease until >10 years old. Severity of disease can be reasonably estimated using endoscopy in the resting horse (grades 1-4), but the gold standard for assessing this disease is endoscopy during exercise, when the high negative pressure—generated when breathing—test the affected laryngeal muscle, which is trying its best to resist the “suctio”’ effect of inspiration (Fig. 1).

Horse undergoing exercising endoscopy to ascertain how the left arytenoid performs when the airway is under pressure. Inset photos show resting (top) and then exercising endoscopy (bottom) of a larynx with grade D arytenoid collapse (green arrow) with additional deformation of the arytenoid cartilage shape and bilateral vocal fold collapse (red arrows).

Horse undergoing exercising endoscopy to ascertain how the left arytenoid performs when the airway is under pressure. Inset photos show resting (top) and then exercising endoscopy (bottom) of a larynx with grade D arytenoid collapse (green arrow) with additional deformation of the arytenoid cartilage shape and bilateral vocal fold collapse (red arrows).

During exercise, RLN is graded from A to D, depending on how much the left side of the larynx can open (Table 1).

• Treatment of RLN

TABLE 1: Grades A-D of laryngeal abduction during exercise. Figures c/o F. Rossignol.

TABLE 1: Grades A-D of laryngeal abduction during exercise. Figures c/o F. Rossignol.

Traditionally, left-sided ventriculocordectomy (“Hobday”/ ventriculectomy plus vocal-cordectomy surgery) and laryngoplasty (“tie-back”) surgeries have been used to treat the disorder, depending on which structures are collapsing and how severely. The intended use of the horse, the budget available and other concerns of the owner/trainer also come into play. New techniques of providing a new nerve supply (“re-innervating”) to the affected muscle are now being trialled in clinical cases. Pacing the muscle with an implanted electronic device has also been attempted in research cases.

• Ventriculocordectomy

Ventriculocordectomy is commonly now referred to as a “Hobday” operation; however, the “Hobday” actually only refers to removal of the blind ending sac that constitutes the laryngeal ventricle. Currently, surgeons tend to remove the vocal cord as well as the ventricle, because it is vocal cord collapse that creates the “whistling” noise. It is a relatively straightforward surgery to perform with minimal risks and complications for the patient. In the last 15 years, there has been a shift to performing it in a minimally invasive way, using a diode laser under endoscopic guidance in the standing sedated horse rather than with the conventional method, via an open laryngotomy incision on the underside of the neck with the horse under a general anesthetic. However, transendoscopic laser surgery is technically difficult with a very steep learning curve for the surgeon. All ventriculocordectomies are not equal (Fig. 2) and for both laser and ‘open surgery’ methods, incomplete resection of the fold can leave behind enough tissue to cause ongoing respiratory noise and/or airway obstruction after surgery.

Two horses after ventriculocordectomy surgery. The horse on the left has an excellent left-sided ventriculocordectomy, with complete excision of the vocal fold tissue (black arrow). The right cord is intact, but the right ventricle has been removed (‘Hobday’). The horse on the right has bilaterally incomplete vocalcordectomies, with much of the vocal fold tissue left behind (green arrows).

Two horses after ventriculocordectomy surgery. The horse on the left has an excellent left-sided ventriculocordectomy, with complete excision of the vocal fold tissue (black arrow). The right cord is intact, but the right ventricle has been removed (‘Hobday’). The horse on the right has bilaterally incomplete vocalcordectomies, with much of the vocal fold tissue left behind (green arrows).

Sports horses, hunters and other non-racehorses were often previously recommended to have a ventriculocordectomy performed rather than a laryngoplasty, even if they had severe RLN. This decision was often made on the grounds of cost, but also due to fear of complications associated with laryngoplasty (‘tie-back’ surgery). A new study has shown that for horses with severe RLN, a unilateral ventriculocordectomy is actually extremely unlikely to eliminate abnormal noise in severely affected horses, because the left arytenoid cartilage continues to collapse.3 The authors recommended that laryngoplasty plus ventriculocordectomy is a better option than ventriculocordectomy alone for all grade C and D horses if resolution of abnormal respiratory noise and significant improvement of the cross sectional area of the larynx are the aims of surgery.3

Advancements in laryngoplasty (‘tie-back’) surgery

Laryngoplasty is indeed one of the most difficult procedures that equine surgeons perform, and suffice to say that with such an advanced surgery, using a registered specialist veterinary surgeon that has considerable experience in airway surgery will likely minimise the chances of a negative outcome. Laryngoplasty surgery has an unjustified poor reputation in my opinion, …

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