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Bilateral paranasal sinus diseases are rarely reported in horses. Treatment using a bilateral frontonasal bone flap on a standing, regular-sized adult horse has not been described previously. A 13-year-old Thoroughbred gelding was evaluated for bilateral mucopurulent nasal discharge. Radiographic, endoscopic and computed tomographic examinations revealed bilateral sinus pathological changes consistent with an ethmoid haematoma involving the maxillary and frontal sinuses. A bilateral frontonasal bone flap was created under standing sedation and local anaesthesia. A tracheotomy was performed initially to ensure a patent airway during the procedure. Additional analgesia had to be given to transect the dorsal part of the nasal septum while elevating the flap. The sinus masses were removed and communications with the nasal cavities created uneventfully. Small sequestra were removed transendoscopically from the left caudal maxillary sinus 4 weeks after the initial procedure. The horse made a complete recovery with an excellent cosmetic outcome. Histopathology revealed the mass to be a sinus cyst. We concluded that a bilateral sinus bone flap can be used in adult regular-sized horses to access the left and right paranasal sinuses simultaneously. Regional nerve blocks should be performed in order to increase analgesia. A temporary tracheotomy prevents any airway obstruction during the procedure. The post-operative cosmesis is excellent. Keywords frontonasal bone flap; sinus cyst; computed tomography; standing surgery; horse.

Sinusitis is a common occurrence in horses and often develops secondary to dental disease. Extraction of cheek teeth in horses is associated with variable degrees of complications and although postoperative displacement and retention of alveolar plugs has been identified as one such potential complication, few cases of resulting sinusitis have been reported. This manuscript describes a four-year-old Thoroughbred mare that was presented for chronic unilateral left-sided mucopurulent nasal discharge after extraction of the left maxillary second molar tooth two months earlier. Radiographic and computed tomographic (CT) examinations revealed a well circumscribed, soft tissue opacity in the left rostral sinus compartment. Intraoral examination revealed feed impacted in the alveolus of the extracted tooth and an oral sinus fistula. Upper airway endoscopy showed thick, purulent material at the nasomaxillary aperture. Sinoscopy showed unexpectedly clean frontal, dorsal conchal and caudal maxillary sinuses. The alveolar dental plug associated with previous exodontia became apparent within the sinus and was removed through the sinoscopy portal. Repeat endoscopies confirmed progressive clearance of the sinusitis during hospitalization. Unilateral nasal discharge returned three months later. An abscess within the sinus had formed. Complete resolution of the sinusitis was achieved after lancing the abscess and further sinus lavage. Sinoscopy through a frontal sinus trephination portal proved useful in diagnosis and treatment. Detailed evaluation of structures allowed for rapid establishment of adequate drainage and communication between all sinus compartments without osteoplastic surgery.

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