Characterization and outcome following excision of masses in the nictitating membranes of horses: 50 cases (1998-2012).

Objective: To determine the histologic findings associated with masses in the nictitating membranes (third eyelids) of horses and to identify prognostic factors associated with recurrence and the outcome.

Design: Retrospective case series.

Animals: 50 horses with masses in a third eyelid.

Procedures: Medical records of horses with partial or complete excision of a third eyelid and submission for histologic evaluation between September 1998 and November 2012 were reviewed. Horses were included if follow-up information for at least 1 year after surgery was available. Information regarding signalment and treatment was obtained from the medical records. Histopathology reports were examined to determine surgical margins and vascular invasion. Data were analyzed by means of a χ(2) test to determine the association between recurrence and type of excision (partial or complete), surgical margins, vascular invasion, and use of chemotherapy as well as the association between partial excision of a third eyelid prior to referral and outcome.

Results: Squamous cell carcinoma was the predominant tumor type of the third eyelid. There was recurrence in 10 of 50 (20%) horses; recurrence was at a mean of 2.25 years and median of 1.5 years after excision. Partial excision prior to referral was associated with outcome.

Conclusions And Clinical Relevance: In horses with masses in a third eyelid, recurrence and mortality rates were high, which suggested that long-term monitoring is important for all patients in which partial or complete third eyelid excision is performed.