Mast cell tumour in the third eyelid of a mare

A 4-year-old Missouri Fox Trotter mare was referred to the Veterinary Teaching Hospital, Koret School of Veterinary Medicine with a reddish mass protruding from the third eyelid and adjacent palpebral conjunctiva of the left eye. On ophthalmic examination, the mare showed mild blepharospasm, mild mucopurulent discharge and mild corneal oedema in the left eye. Menace response, pupillary light reflexes and intraocular examination were normal. A rounded, fleshy red ulcerated mass, approximately 3 cm in diameter, expanded the edge of the outer surface of the medial third eyelid and conjunctiva of the ventromedial palpebral region. Physical examination was otherwise unremarkable. Based on history and clinical findings, surgical removal was elected. The tumour was excised and the conjunctiva in the area of tumour treated with cryotherapy. Histological evaluation revealed a mast cell tumour on the third eyelid. Nine months follow-up revealed no recurrence.