Roarers - surgery for recurrent laryngeal neuropathy – impact and outcomes
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By 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.
Treatment of RLN
Laryngoplasty (tie-back) being performed in standing sedated horses.
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 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.
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.
During exercise, RLN is graded from A to D, depending on how much the left side of the larynx can open.
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.
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.
Advancements in laryngoplasty (‘tie-back’) surgery
Laryngoplasty is indeed one of the most difficult procedures that equine surgeons perform ….
