Radicular (periapical) cyst causing exophthalmos in a dog

A 10-year-old male neutered Bichon Frise presented for assessment of right unilateral exophthalmos. The ophthalmological assessment revealed signs of retrobulbar disease. Computed tomography of the head showed a cavitary, well-defined, fluid-filled structure, which displayed a strong peripheral rim of contrast enhancement, and was centred around the tooth roots of the right maxillary first and second molar teeth (109 and 110). Focused ultrasound-guided fluid sampling and fine needle aspirates were obtained for diagnostic purposes. After discussing the case with a veterinary dentist, extraction of the 109 and 110 and debridement of the cyst were performed. Histopathology supported the suspicion of a radicular cyst. Radicular cysts, despite being benign lesions, need to be included as a possible differential in cases with exophthalmos due to their potential retrobulbar mass effect.