A 12-year-old 7.5-kg (16.5-lb) neutered male Boston Terrier was evaluated by the referring veterinarian because of acute left-sided facial swelling and mild mucopurulent nasal discharge. Prednisone and amoxicillin-clavulanic acid treatment resulted in minimal response. Three weeks later, left-sided nasal discharge and facial swelling persisted with rightward deviation of the nasal planum. Over the following several weeks, signs of pain on palpation of the left-sided facial swelling became apparent and progressively worsened; ipsilateral exophthalmos had also developed. The dog was then referred to the University of Missouri Veterinary Health Center for further evaluation.
Physical examination revealed