Meibomian epithelioma of the lower eyelid in a thoroughbred horse

A 9-year old, castrated male, thoroughbred horse presented for a left lower eyelid mass with ocular signs of mucopurulent discharge, conjunctival hyperemia and ocular discomfort. On physical examination, there was no other abnormality. Surgically, the mass arising from the inner surface of left lower eyelid was excised and examined histopathologically. Microscopically, the eyelid mass exhibited neoplastic basaloid cells forming irregular cell masses of variable size separated by thin fibrous tissues. The basaloid cells showed mildly pleomorphic and undifferentiated appearances with prominent oval nuclei and scant cytoplasm. Poorly differentiated meibocytes were observed occasionally in the periphery regions of the cell masses suggesting the mass of lower eyelid originated from meibomian glands. Based on histopathological observation, the present case was diagnosed as an equine meibomian epithelioma in the lower eyelid. To the author's knowledge, the present case is the first report of equine meibomian epithelioma in veterinary literatures.