Unilateral orbital lacrimal gland abscess in a horse

A 20-year-old Thoroughbred gelding presented for evaluation of a periorbital dorsal swelling of the left eye that had been intermittently present for 3 months. Upon ocular examination, a firm, non-painful swelling was identified under the upper eyelid in the region of the orbital lacrimal gland, and was noted to extend anteriorly from underneath the dorsal orbital rim. Ultrasonographic examination revealed a mixed echogenic mass along the dorsal orbital rim that followed the contour of the globe. CT scan showed a moderately contrast enhancing mass that was contiguous with the eyelid. Differential diagnoses included neoplasia, inflammatory lesions such as a granuloma, foreign body or abscess. Surgical exploration and excision of the mass revealed a lobular structure with a purulent center. Histopathology identified the mass as the orbital lacrimal gland with concurrent severe dacryoadenitis. Culture of the purulent center of the mass revealed beta-hemolytic Staphylococcus aureus. The patient was maintained on supportive care and antibiotic treatment based on sensitivity postoperatively. No recurrence was reported 40 months later. This paper aims to identify bacterial dacryoadenitis as a cause for unilateral periorbital swelling in the horse. Differential diagnoses for this presentation, as well as successful surgical management are discussed. To the author's knowledge, this is the first case of bacterial dacryoadenitis and subsequent abscessation of the orbital lacrimal gland in the horse.