A bilateral stylohyoid fracture

Summary A 6‐year‐old Thoroughbred gelding (610 kg) was referred to the Ontario Veterinary College—Health Sciences Centre for evaluation of lethargy, acute upper airway noise and dysphagia. On presentation, the horse was quiet, alert and responsive. Vital signs were within normal limits except for tachypnoea (24 breaths/min) and a fever (39.1°C). Physical examination revealed a pronounced tracheal rattle, bilaterally increased bronchovesicular sounds and mild bilateral nasal discharge containing feed material. Neurological examination was unremarkable. Initial diagnostics included radiography and endoscopy of the head and upper airway. Lateral oblique skull radiographs revealed bilateral, displaced transverse fractures of the stylohyoid bones. Endoscopy showed marked dorsal and lateral pharyngeal collapse without other upper airway abnormalities. These findings suggested dysfunction of the hyoid apparatus, potentially involving the glossopharyngeal nerve or stylopharyngeus muscle, both essential for pharyngeal stability during respiration and swallowing. Conservative treatment was initiated with a 15‐day course of trimethoprim sulfamethoxazole (30 mg/kg bwt p.o. b.i.d.; Pharma) and an 8‐day course of flunixin meglumine (1.1 mg/kg bwt i.v. b.i.d.; Merck). Although clinical signs initially resolved, they recurred 3 months later. Repeat radiographs showed no fracture healing. A staged right‐sided ceratohyoid–basihyoid disarticulation was performed to reduce mechanical stress on the fractures. The horse was maintained on a soft diet post‐operatively. Two months after surgery, radiographs confirmed complete healing of both stylohyoid fractures, and endoscopy showed resolution of pharyngeal collapse. Given the successful outcome, the contralateral procedure was not performed. The cause of the bilateral fractures remains unknown, with no history of trauma or infection. This case is notable for the rare presentation of bilateral stylohyoid fractures manifesting solely as pharyngeal collapse. It underscores the importance of considering hyoid apparatus dysfunction in horses with pharyngeal signs and highlights the potential value of unilateral surgical intervention in selected cases.