The epiglottis is a triangular-shaped cartilage located in the throat at the base of the entrance to the airways.
During normal breathing, it is situated above the soft palate and facilitates air movement.
When eating, the epiglottis moves upwards and backwards to allow swallowing and to prevent food from entering the airways.
To allow for such movement, the lower surface of the epiglottis has a loosely attached elastic mucosa (subepiglottic mucosa).
Epiglottic entrapment occurs when the subepiglottic mucosa becomes positioned above the epiglottis, restricting movement, Alex Gillen writes in the latest issue of Equine Disease Quarterly.
Gillen, a lecturer in equine surgery at the Phillip Leverhulme Equine Hospital, part of the University of Liverpool, says the most common presenting sign in cases of epiglottic entrapment is abnormal respiratory noise.
The abnormally positioned subepiglottic mucosa creates a slightly narrowed airway, as well as increased air turbulence, which creates a harsh respiratory noise.
Horses in a higher plane of work, racehorses for example, can also present with exercise intolerance.
In horses performing at high speeds, even mild narrowing of the airway can result in decreased athletic performance.
Coughing and nasal discharge occur in some cases, as an abnormally functional epiglottis can contribute to the disruption of airflow and slightly interfere with the swallowing process.
As none of these changes indicate a specific cause of disease, transnasal endoscopy is often used to further investigate horses exhibiting these clinical signs.
This procedure is commonly done in many cases with suspected upper airway disease and involves the passage of a small, flexible camera up the horse’s nose to visualize the airway.
Most horses tolerate this intervention well with minimal restraint or sedation.
The majority of cases have persistent epiglottic entrapment; however, a small number of horses experience intermittent epiglottic entrapment, which is relieved when the horse swallows.
The membrane entrapping the epiglottis can vary in thickness and can become ulcerated.
In addition to endoscopic evaluation, a radiograph of the laryngeal region can also be obtained to assess the patient for epiglottic hypoplasia (a smaller than normal epiglottis) as this can be an uncommon cause of epiglottic entrapment.
Surgery is the most common treatment option for this condition. An incision is made through the abnormally positioned subepiglottic mucosa to release the entrapped epiglottis.
The procedure can be performed either under sedation and local anesthesia or under general anesthesia and typically takes less than 30 minutes.
There are several surgical methods available, namely use of a transnasal endoscopically guided laser, transendoscopic electrosurgical instrument, or transnasal or transoral curved surgical knife.
Surgical excision can also be performed via an incision into the airway via the pharynx or larynx, however, these methods will result in an external scar and can contribute to surgical site complications.
These procedures are therefore typically reserved for cases with additional complications.
The potential complications of surgical intervention include thermal trauma to the epiglottis, adhesions, and cicatrix (scar) formation.
To reduce the risk of this occurring, horses should receive systemic and topical anti-inflammatory medications.
Dorsal displacement of the soft palate can occur regardless of the treatment method employed, particularly when epiglottic hypoplasia is present.
Local inflammation is common following surgical correction of epiglottic entrapment. Horses should, therefore, receive transnasal endoscopic evaluation each week following surgery until the larynx has a normal appearance.
Throat sprays containing anti-inflammatory agents are also strongly recommended.
In order to reduce inflammation in the laryngeal region; horses require a period of rest following surgery.
Depending on the severity of the condition and the treatment method employed, horses can return to work 3-8 weeks post-operatively, providing transnasal endoscopic evaluation is normal.
Reoccurrence is not uncommon and can be treated by surgical excision of the excess subepiglottic mucosa.
The majority of horses with epiglottic entrapment without epiglottic hypoplasia are able to return to their original level of activity.
Equine Disease Quarterly is funded by underwriters at Lloyd’s, London.