Endotracheal cyst treated via diode laser ablation in an 8-month-old Quarter Horse filly

An 8-month-old American Quarter Horse filly was presented for evaluation of progressive abnormal respiratory noise and increased respiratory effort that failed to respond to empirical medical therapy. The filly was reported to display intermittent stridor, increased respiratory effort, decreased appetite and increased irritability. No other horses on the premises exhibited similar clinical signs. Upper airway endoscopy identified an endotracheal cyst located within the thoracic trachea at approximately 85 cm from the nares, resulting in an estimated 40%–50% obstruction of the tracheal lumen. The distal trachea, carina and guttural pouches were unremarkable, and mild pharyngeal hyperplasia was observed. Endoscopically guided laser fenestration of the cyst was performed, resulting in drainage of clear fluid. Intravenous anti-inflammatory medication was administered, and the filly was monitored for 24 h, during which abnormal respiratory noise resolved. Repeat endoscopy performed the following day and at 6 weeks post-surgery demonstrated a flat residual cyst remnant without swelling, discharge or evidence of recurrence.