EQUINE VETERINARY EDUCATION Equine vet. Educ. (2020) 32 (1) 25-29 doi: 10.1111/eve.12920


Case Report A novel approach for palatal cyst ablation in a horse


M. Sinovich , P. G. Kelly and D. C. Archer* The Philip Leverhulme Equine Hospital, Institute of Veterinary Science, University of Liverpool, Neston, UK *Corresponding author email: darcher@liverpool.ac.uk


Keywords: horse; palatal cyst; tracheostomy; laser; respiratory noise


Summary An 18-month-old Welsh Cob was referred to a university teaching hospital for investigation of abnormal respiratory noise at rest. Video-endoscopy revealed persistent displacement of the soft palate with bilateral 2–3 cm diameter raised areas on either side of the midline. Neither trans-nasal nor oral approaches allowed sufficient visualisation of the caudal soft palate for diagnosis or treatment. Latero-lateral radiographs showed a blunted, thickened caudal edge of the soft palate consistent with a palatal cyst. Two palatal cysts were thermally ablated with a transendoscopic diode laser via temporary tracheotomy. The horse recovered uneventfully and resolution of the displacement was evident on follow-up endoscopy 11 months later. This report documents a novel surgical approach to the caudal aspect of the soft palate.


Introduction


Palatal cysts have previously been reported as a cause of abnormal respiratory noise, increased respiratory effort, and dysphagia secondary to persistent dorsal displacement (DDSP) of the soft palate in the horse (Koch and Tate 1978). Respiratory noise is commonly exacerbated by exercise and is usually noted on both inspiration and expiration (Salz et al. 2013). Cystic structures involving the upper respiratory tract (URT) of equines are most usually found in the subepiglottic tissues. Less frequently they occur in the dorsal nasopharynx and may distort the architecture between the two (Palmer 2003). Dysphagia, persistent coughing and aspiration pneumonia have also been reported as sequelae to subepiglottic cysts (Salz et al. 2013). It has been proposed that there is an association


between these cysts and the embryonic remnants of the thyroglossal and craniopharyngeal ducts (Kelmer et al. 2007), and they are thought to be a congenital defect (Fulton et al. 2012). Acquired cystic structures in the upper respiratory tract have also been reported as sequelae to inflammation and or trauma (Sullivan and Parente 2003). They have also been reported in older horses, as an incidental finding, with no history of upper respiratory tract problems and their aetiology is unknown (Aitken and Parente 2011). Surgical removal by conventional surgical approaches via laryngotomy, pharyngotomy, transoral or transnasal approaches as well as transendoscopic laser ablation has been described (Koch and Tate 1978; Haynes et al. 1990; Tulleners 1991; Blikslager and Tate 2000; Sullivan and Parente 2003; Fulton et al. 2012). Lasers have a number of applications in the horse


including resection of cutaneous masses (McCauley et al. 2002) and within the URT including laryngeal ventriculectomy, cordectomy and resection of subepiglottic tissue causing epiglottic entrapment (Palmer 2003). Transendoscopic laser


surgery of the equine upper respiratory tract has many proposed advantages, especially in racehorses, because of the noninvasive nature of surgery, avoidance of general anaesthesia, and the relatively rapid return to work (Palmer 2003). Removal of subepiglottic cysts have been reported using


conventional surgical approaches via laryngotomy or pharyngotomy incisions, oral approaches, or transendoscopically with an Nd:Yag or diode laser or transendoscopic instruments such as snares (Fulton et al. 2012). This case report describes the use of a retrograde


endoscopic approach via a tracheotomy for further evaluation and treatment of bilateral palatal cysts using a diode laser in a horse.


Case history


An 18-month-old, 346 kg, Welsh Cob gelding was presented to the Philip Leverhulme Equine Hospital for further investigation of respiratory noise at rest. The noise was reported to worsen when the horse was excited and intermittent coughing had been evident when the gelding had been eating. Intermittent nasal discharge containing ingesta had also been noted. The clinical signs had been present since the purchase of the gelding 2 months previously. No pre-purchase examination had been performed. Clinical examination at rest was unremarkable and thoracic auscultation did not reveal any abnormalities. A mild inspiratory and slightly louder expiratory noise was audible during this examination. Endoscopy of the upper respiratory tract was performed


per nasum with the horse standing and under sedation (xylazine, 0.4 mg/kg bwt and butorphanol 0.014 mg/kg bwt intravenously [i.v.]). This revealed persistent DDSP. The epiglottis could not be visualised at any stage even when swallowing was induced. The dorsal border of the soft palate appeared to project dorsally on either side of the midline (Fig 1). No abnormalities of the guttural pouches were evident on endoscopic examination. Latero-lateral radiographic projections were performed


centred on the larynx. These demonstrated an abnormal appearance to the caudal border of the soft palate which had a blunted, bulbous ‘match-head’ appearance, consistent with the appearance of a soft palate cyst (Haynes et al. 1990) (Fig 2). The epiglottis was positioned ventrally relative to the soft palate but appeared to be of normal shape and length. A provisional diagnosis of bilateral palatal cysts was


therefore made. It was not clear how much palatal tissue was on the ventral aspect of the soft palate as they could not be visualised. This led to concern about potentially


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