What is Subepiglottic Cyst ?
Although cysts are found in all breeds of horses, they are most commonly seen in Standardbreds and Thoroughbreds of all ages. Most cysts are believed to originate from the tissue remnants of the embryonic thyroglossal duct, and are likely to be present from birth. Depending on where they originate in that region, they can also be called soft palate or dorsal pharyngeal cysts. Here, they can stay undetected until an affected horse matures and begins exercise training. As the cyst grows larger, your horse will be less likely to be tolerant of exercise, and may develop chronic conditions of coughing or choking.
Subepiglottic cysts are round masses that form near the entrance to the pharynx, or the cavity that connects the mouth and nose to the esophagus. These cysts are thin walled structures filled with fluid, and can be large enough to push the soft palate upwards. A common sign of these cysts is persistent respiratory noise, although larger cysts can cause more serious problems involving breathing and swallowing, and may need to be removed for the safety of your horse. Surgical removal can be done a number of ways, and usually leads to a complete recovery.
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Symptoms of Subepiglottic Cyst in Horses
While a subepiglottic cyst can have little effect on your horse, larger cysts can cause problems as the pharynx becomes obstructed. Symptoms of a subepiglottic cyst include:
- Respiratory noise, often during exercise
- Exercise intolerance
- Choking up at exercise
- Chronic coughing
- Chronic choking
- Difficulty swallowing
- Airway obstruction
- Presence of smooth walled cysts filled with fluid at the entrance of the pharynx, ranging in diameter from 1 to 5 cm
Additional signs seen in foals include:
- A reflux of milk from the nose within the first few days of birth
- Nasal discharge
- Aspiration pneumonia
The types of subepiglottic cysts are named for their locations.
- Subepiglottic cysts – These are cysts found in the subepiglottic tissues, and are developed from embryonic remnants of the thyroglossal duct
- Soft palate cysts – These are cysts found within the soft palate; larger cysts can push the soft palate upwards
- Dorsal pharyngeal cysts – These cysts are found in the dorsal nasopharynx region, and are developed from craniopharyngeal ducts
Causes of Subepiglottic Cyst in Horses
Causes of the formation of a subepiglottic cyst include:
- The remnants of the embryological thyroglossal duct, a developmental connection between the area where the thyroid gland originates and its final placement
- The remnants of the embryological craniopharyngeal duct, the area where the pituitary gland eventually forms
- A result of a dilation of the mucous glands
Diagnosis of Subepiglottic Cyst in Horses
Diagnosis is primarily through the identification of the cyst. This is accomplished with an oral examination, and an endoscopic exam of the pharynx and upper respiratory tract, often under general anesthesia. The cyst will appear as a smooth walled mass containing a yellow fluid. Sometimes, the cyst can be loosely attached and can disappear under the soft palate. In other cases, horses can have a concurrent case of soft palate displacement. Both situations can hinder the visual identification of a subepiglottic cyst. X-rays can therefore be used to help identify the location and size of the mass.
Treatment of Subepiglottic Cyst in Horses
Treatment is generally a surgical removal of the cyst. A rupture of the cyst can decompress the mass, but often the cyst will recur. Care must also be taken to remove the entire cystic lining to prevent the cyst from redeveloping.
Removal options include a laryngectomy or pharyngotomy, though these methods carry a risk of tissue damage, bleeding, and a long recovery time. Other methods that have less surgical stress and a shorter recovery time include an oral endoscopy with the aid of a transendoscopic laser, or an electrocautery snare which uses a stainless steel wire to amputate the cyst.
Surgical removal in foals should include removal of the surrounding aryepiglottic and glossoepiglottic mucosa tissues to prevent a cyst recurrence. Following any of the surgical procedures, rest is recommended for 4 to 6 weeks.
Recovery of Subepiglottic Cyst in Horses
Recovery of a subepiglottic cyst is favorable when the cyst is surgically removed. Your veterinarian may send home medications to administer or instructions for the care of your horse after any surgery. Healing time is quick, and your horse can return to work within 1 to 2 weeks, with a full return to athletic activities following that. Recurrence of the cyst is unlikely if the entire cyst and related tissues are removed, but be sure to alert your veterinarian to any returning symptoms.