Congenital sinus cyst in a foal.

Radiography and endoscopy of a 17-day-old Standardbred foal that had right-sided facial swelling and dyspnea since birth revealed a soft tissue mass in the right nasal passage and right maxillary and frontal sinuses. A bone flap was used to expose the mass, and a fluid-filled structure was removed surgically. After surgery, the dyspnea was alleviated. The facial deformity resolved by the time the foal was 6 months old. The upper airway obstruction was absent clinically and endoscopically by the time the foal was 17 months old.