What does the epiglottis do in the unaffected horse when eating and swallowing?
When the horse is not swallowing, the muscles in the esophagus (tube leading to the stomach) contract and move the epiglottis up. This action allows air to flow into the trachea and down to the lungs. When the horse takes a bite of food and the food reaches the pharynx (back of the throat), the swallowing reflex begins. The upper portion of the horse’s airway (the larynx) moves up and tips the epiglottis over the trachea (windpipe) opening (glottis). The action of the epiglottis moving over the opening prevents food from entering the airway. Once the swallowing reflex is initiated, the esophageal opening (sphincter) relaxes and the food enters the esophagus. Once the food is swallowed, moves into the esophagus, the larynx moves downward and reopens the airway.
What is the Soft Palate?
The soft palate is an extension of the hard palate that divides the oral cavity and the nasal cavity. If you move your tongue to the roof of your mouth, you can feel the hard palate. Then move your tongue further back and the roof of your mouth becomes soft. The softer portion of the roof is called the soft palate. The function of the soft palate is to form a seal with the base of the epiglottis.
What is the Epiglottis?
The epiglottis is a triangular shaped tissue that flips up to protect the airway during swallowing. This action prevents food from entering the trachea (windpipe) and move into the lungs. The first photos demonstrate the soft palate, epiglottis and their relationship with the airway. When the horse exercises, the soft palate moves down and the airway opens up to increase the air flow into the lungs. The epiglottis sits firmly on top of the soft palate maintaining that seal between the oral and nasal cavities and allowing the horse to breathe entirely through its nose. Again, if you were to move your tongue to the back of your mouth, touch the soft roof, the epiglottis would be sitting above the soft palate.
The airway is in blue, the horse’s tongue is red, and the esophagus is green.
Normal soft palate – these views are looking straight down the horse’s airway via an endoscope, the colored line diagram (above these two photos) visualizes the airway from the side.
What is the Dorsally Displaced Soft Palate (DDSP) and what are the signs?
During exercise, the soft palate moves up and covers the epiglottis, this motion results in preventing the seal between the oral and nasal cavity. As you can see in the photo below, the soft palate blocks the tracheal opening and decreases the volume of air the horse can take in. When the soft palate covers the epiglottis, the horse exhibits a gurgling noise during exercise. This unusual noise is commonly heard when the horse exhales. Horses with a DDSP will have decreased speed and in some instances will stop and struggle to breathe. Fortunately, during eating and swallowing, the soft palate and epiglottis return to their normal position.
Endoscopic view of a dorsally displaced soft palate
How can the Dorsally Displaced Soft Palate be diagnosed?
The Arizona Equine Medical and Surgical Centre veterinarians can diagnose dorsal displacement of the soft palate via standing endoscopic examination of the upper airway. The appearance as seen in the above photos is typical with the epiglottis lying on top of the soft palate. During this examination the horse is not sedated, a sedated horse will displace its soft palate and it can remain displaced for some time.
What is the treatment for DDSP?
There are many different surgical procedures that have been used to try and correct DDSP. They are principally designed to try and either ‘stiffen’ up the flabby soft palate or epiglottis or recreate the seal between the epiglottis and soft palate and the Arizona Equine surgeons work with the clients to determine the optimal option for their horse.
Palatoplasty – ‘Stiffening’ of the soft palate (palatoplasty) This is a procedure in which a thin edge of the back of the soft palate is removed surgically or with a laser. This is thought to stiffen the soft palate and make it less likely to come up above the epiglottis.
Myectomy – Many horses will be improved by cutting a segment out of the muscles that pull the larynx back. These are the “strap” muscles that run along the bottom of the neck from the chest to the head. This allows the larynx to stay forward and form a better seal with the soft palate. A slight downside to this surgery is that removing part of the muscles leaves a divot that is visible externally.
Laryngeal advancement (Tie Forward) This surgery involves permanently fixing the larynx forward via two sutures placed either side of the larynx. The sutures are tied to a small bone (basihyoid) which lies in front of the larynx. The goal of this method is to decrease the distance between the epiglottis and the opening of the larynx. When the distance between epiglottis and laryngeal opening is decreased, the soft palate is less likely to displace on top of the epiglottis.
Prognosis: Interestingly enough, studies have shown all three of the above procedures to work in about 70% of the cases when done individually. Some surgeons feel that combining two of the procedures may give a higher success rate.
The patients are typically sent home with antibiotics and anti-inflammatories (butazolidin/banamine) and rest. The Arizona Equine surgeons, Dr. Scott Taylor and Dr. Rick Howard are highly qualified and ready to help owners with their horses.