Surgical management of an ethmoid cyst in a horse.

A 2-year old Thoroughbred filly was examined for a 1-month history of persistent nasal discharge. Contrast radiography revealed a circumscribed mass within the right maxillary sinus which extended to the frontal sinus and ethmoid labyrinth. A discrete attachment of the mass to the ethmoid labyrinth was identified at surgery. Surgical removal of the mass eliminated the nasal discharge. On gross examination, the external structure of the mass was similar to a turbinate with a thin bony wall covered by a smooth mucosal membrane. The internal structure of the lesion had a lining membrane with multiple 1-3 cm in diameter fluid filled cystic structures. The histological appearance of the multiloculated structure was similar to the ethmoid labyrinth. This, combined with the single site of attachment to the ethmoid labyrinth, suggested that the cyst was ethmoidal in origin.