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.