Maxillary bone epithelial cyst in a dog.

A swelling ventromedial to the left eye of a one-year-old, neutered male Labrador failed to respond to antibiotic and anti-inflammatory therapy. Plain and contrast radiography revealed a spherical, radiolucent area, 1.5 cm in diameter, dorsomedial to the fourth maxillary premolar and rostral to the ethmoid region. The lesion was thin-walled, with a smooth radiopaque margin, and was clearly demarcated from the surrounding structures. Dacryocystography demonstrated no apparent physical association between the lesion and the nasolacrimal duct, the latter appearing normal. Ultrasonography of the lesion showed a round, anechoic structure consistent with the appearance of a cyst. Prior to surgical excision of the lesion, intralesional fluid was aspirated. Bacteriology of the fluid was negative for both aerobic and anaerobic organisms. Cytological examination of the fluid showed a few macrophages and small lymphocytes; neither significant inflammatory component nor neoplastic cells were found. Histology showed the lesion to be a benign epithelial cyst. The dog recovered uneventfully and there was no clinical evidence of recurrence within a two-year follow-up period.