Epiglottic entrapment (EE) is a common upper respiratory tract disorder affecting athletic horses, particularly Thoroughbreds and Standardbreds.
Overview and Clinical Importance
Epiglottic entrapment (EE) is a common upper respiratory tract disorder affecting athletic horses, particularly Thoroughbreds and Standardbreds. In this condition, the aryepiglottic fold (subepiglottic tissue) becomes abnormally positioned and envelops the dorsal surface of the epiglottis, obscuring its normal serrated margins and vascular pattern. The condition has a reported incidence of 0.9-5% in racehorses and represents a significant cause of poor performance and abnormal respiratory noise during exercise.
Understanding epiglottic entrapment is essential for the NAVLE because it tests knowledge of equine upper airway anatomy, diagnostic endoscopy interpretation, and surgical treatment options commonly encountered in equine practice.
High-YieldOn endoscopy, epiglottic entrapment shows loss of the normal serrated margins and vascular pattern of the epiglottis, replaced by smooth mucosa of the entrapping membrane. The general triangular shape of the epiglottis remains visible, unlike dorsal displacement of the soft palate (DDSP) where no epiglottic outline is seen.
| Factor |
Mechanism |
| Epiglottic hypoplasia |
Underdeveloped epiglottic cartilage allows subepiglottic tissue to more easily fold over the smaller epiglottis |
| Excess aryepiglottic tissue |
Redundant or hypertrophied mucosal tissue increases likelihood of entrapment |
| Inflammation/edema |
Upper respiratory tract inflammation causes swelling of aryepiglottic tissue |
| Subepiglottic cysts |
Space-occupying lesions can alter tissue position and predispose to entrapment |
| Epiglottitis |
Inflammation of epiglottic mucosa can lead to secondary entrapment |
Anatomy and Pathophysiology
Normal Laryngeal Anatomy
The epiglottis is a triangular, leaf-shaped elastic cartilage that forms the rostral boundary of the larynx. In horses, the epiglottis normally rests dorsal to the soft palate and is essential for maintaining obligate nasal breathing and protecting the lower airways during swallowing. The epiglottis is covered by well-vascularized mucous membrane that is closely adherent to the cartilage on both its dorsal and ventral (lingual) surfaces.
The aryepiglottic fold is a mucous membrane that extends from the lateral aspect of the arytenoid cartilages to the ventrolateral aspect of the epiglottis, where it blends with the subepiglottic mucosa and glossoepiglottic fold. Ventral to the epiglottis, this mucosa is loosely attached and normally compressed in an accordion-like fashion.
Pathophysiology of Entrapment
Epiglottic entrapment occurs when the subepiglottic tissue (aryepiglottic folds and glossoepiglottic mucosa) becomes edematous, hypertrophied, or redundant and folds dorsally over the apex and lateral margins of the epiglottis, effectively enveloping it. This creates a "pillowcase" appearance over the epiglottis.
Predisposing Factors
NAVLE TipRemember that epiglottic hypoplasia is both a predisposing factor AND can be assessed radiographically. Lateral pharyngeal radiographs can help identify hypoplastic epiglottis and provide additional prognostic information, especially in chronic cases.
| Common Signs |
Less Common Signs |
Clinical Notes |
| Abnormal respiratory noise during exercise
(rattling, wheezing, gurgling) |
Coughing |
Noise is typically expiratory due to billowing of entrapping membrane |
| Exercise intolerance/poor performance |
Nasal discharge |
Decreased cross-sectional area of pharynx obstructs airflow |
| Decreased racing performance |
Headshaking |
Some horses may be asymptomatic or show intermittent signs |
|
Dysphagia (rare) |
Food/water from nostrils indicates more severe dysfunction |
Clinical Presentation
Signalment and Breed Predisposition
Epiglottic entrapment occurs predominantly in Thoroughbred and Standardbred racehorses, with males and females equally affected. The condition is primarily seen in young athletic horses, with a mean age of approximately 3-4 years at diagnosis. It is rarely diagnosed in older horses or non-athletic breeds. The condition has also been reported in Chilean Criollo ponies.
Clinical Signs
High-YieldThe respiratory noise in epiglottic entrapment is characteristically EXPIRATORY because air becomes trapped and causes the entrapping membrane to billow and vibrate during exhalation. This is in contrast to laryngeal hemiplegia (roaring), which produces primarily INSPIRATORY noise.
| Condition |
Endoscopic Appearance |
Key Differentiating Feature |
| Epiglottic Entrapment |
Epiglottis outline visible but margins obscured by smooth membrane |
Triangular epiglottic shape visible; looks like "pillowcase" |
| DDSP |
Soft palate dorsal to epiglottis; no epiglottic outline visible |
Complete loss of epiglottic visualization |
| Epiglottitis |
Edema, reddening, thickening of epiglottic mucosa; margins may be visible |
Inflammation visible; may require forceps to differentiate from entrapment |
| Laryngeal Hemiplegia |
Asymmetric arytenoid movement; left arytenoid fails to abduct |
Epiglottis appears normal; primarily inspiratory noise |
Diagnosis
Endoscopic Examination
Upper airway endoscopy is the gold standard for diagnosing epiglottic entrapment. The examination can be performed at rest or during exercise (dynamic endoscopy), with dynamic endoscopy being essential for detecting intermittent entrapment that may not be visible at rest.
Key Endoscopic Findings
- Loss of normal serrated (scalloped) lateral margins of the epiglottis
- Obscured dorsal epiglottic vascular pattern
- Smooth mucosa of entrapping membrane covering the epiglottis
- General triangular shape of epiglottis remains visible
- Soft palate is normally positioned ventral to the epiglottis
- In chronic cases: ulceration and thickening of the entrapping membrane
Differential Diagnosis
NAVLE TipWhen differentiating epiglottic entrapment from epiglottitis, use bronchoesophageal forceps to elevate the tissue. In entrapment, the membrane can be lifted off the epiglottis; in epiglottitis, the swelling is adherent to the epiglottic cartilage itself. This distinction is critical because incorrect surgical intervention for epiglottitis (when mistaken for entrapment) can cause irreparable damage.
Additional Diagnostic Modalities
Lateral Pharyngeal Radiography: Can identify epiglottic hypoplasia and provide additional prognostic information. Useful for chronic or complicated cases.
Dynamic (Exercising) Endoscopy: Essential for detecting intermittent entrapment that only occurs during high-intensity exercise. Can be performed on a high-speed treadmill or overground with a portable endoscope system.
Swallow Test During Endoscopy: Prompting the horse to swallow several times during endoscopy may help recreate intermittent entrapment or reveal subepiglottic cysts.
| Technique |
Anesthesia |
Recurrence Rate |
Key Considerations |
| Transendoscopic Laser (Nd:YAG or Diode) |
Standing sedation with topical anesthesia |
Approximately 4-5% |
PREFERRED technique; requires specialized equipment; risk of thermal damage to epiglottis |
| Transnasal Shielded Hook Bistoury |
Standing sedation with topical anesthesia |
5-15% |
Quick, inexpensive; reduced iatrogenic injury compared to unshielded; check instrument function pre-op |
| Transoral Hook Bistoury |
General anesthesia typically |
0-15% |
Avoids damage to soft palate; requires adequate oral cavity size; risk of epiglottic laceration if horse swallows |
| Transendoscopic Electrosurgery |
Standing sedation |
Approximately 40% |
HIGH recurrence rate; not recommended as first-line treatment |
| Laryngotomy/Pharyngotomy |
General anesthesia |
Approximately 36% |
Reserved for thickened/scarred folds or failed previous surgery; allows tissue resection |
Treatment
Surgical correction is the primary treatment for persistent epiglottic entrapment. The goal of surgery is to axially divide the entrapping membrane to release the epiglottis. Several techniques are available, each with different advantages, complications, and recurrence rates.
Surgical Techniques Comparison
High-YieldThe PREFERRED surgical technique is transendoscopic laser axial division, which has the lowest recurrence rate (approximately 5%) and can be performed standing. Know that transendoscopic ELECTROSURGERY has a HIGH recurrence rate (40%) and is NOT recommended.
Conservative Management
Some horses with intermittent entrapment may be managed conservatively with exercise restriction and anti-inflammatory treatment (NSAIDs, topical throat sprays with corticosteroids). However, most cases of persistent entrapment require surgical correction for resolution.
Perioperative Management
| Phase |
Protocol |
| Standing Sedation |
Detomidine (0.02 mg/kg IV) + Butorphanol (0.01-0.02 mg/kg IV) |
| Topical Anesthesia |
2% Lidocaine spray (30-50 mL) applied to epiglottis and surrounding structures via endoscope |
| Postoperative Medications |
Flunixin meglumine 1.1 mg/kg IV/PO BID for 5 days
Procaine penicillin G 22,000 IU/kg IM BID for 3-5 days |
| Rest Period |
4-6 weeks before gradual return to training; reduces inflammation and re-entrapment risk |
| Follow-up Endoscopy |
2 weeks postoperatively to confirm epiglottis is free and healing appropriately |
Prognosis
The prognosis for return to athletic performance following surgical correction of uncomplicated epiglottic entrapment is generally GOOD. Studies report that approximately 74-82% of horses race following surgery. Key prognostic factors include:
- Prior racing experience: Horses that raced before surgery are 4.1 times more likely to race after surgery than those that had not
- Postoperative complications: Horses with severe inflammation, airway complications, or re-entrapment have lower odds of racing
- Concurrent upper airway abnormalities: Horses with additional lesions (DDSP, epiglottic deformity) have poorer prognosis
- Breed: Thoroughbreds may take longer to return to racing compared to Standardbreds (79% longer)
Potential Complications
NAVLE TipAlways warn owners that 10-20% of horses may develop DDSP following surgical correction of epiglottic entrapment, regardless of the technique used. This is because the entrapping membrane may have been providing structural support to the soft palate.
| Complication |
Notes |
| Re-entrapment |
5-15% with bistoury techniques; 4-5% with laser; may require repeat surgery |
| DDSP (Secondary) |
10-20% of horses develop DDSP after entrapment correction; warn owners pre-operatively |
| Epiglottic trauma/thermal injury |
Laser burns or lacerations; typically heal within 2-4 weeks |
| Granulation tissue |
May form at transection site; can require additional treatment |
| Soft palate laceration |
Risk with transnasal techniques; shielded bistoury reduces this risk |