Characterisation and Outcome Following Excision of Masses in the Nictitating Membranes of Horses: 50 cases (1998 – 2012)

Characterisation and Outcome Following Excision of Masses in the Nictitating Membranes of Horses: 50 cases (1998 – 2012)

Summarised by Liesel van der Merwe BVSC (MMedVet(Med)

JAVMA , Vol 245(7):812 -815 Scherrer, NM et al

Determined the histiologic findings associated with masses in the 3rd eyelid of horses to identify prognostic factors associated with outcome

Why they did it.

The nictitating membrane (3rd eyelid) is an important site of peri-ocular neoplasia with squamous cell carcinoma (SCC) being most prevalent. The 3rd eyelid of horses, in contrast to that of dogs, does not play a significant role in tear film production. Complete excision is believed to be curative, but lymphnode and bone involvement may occur if delayed. There is increased risk of SCC in horses with no or slight pigmentation and a breed predisposition in Drafts, Appaloosas and Haflingers.

What they did:

This article is a retrospective evaluation of medical records of all horses admitted to University of Pennsylvania New Bolton Centre between 1998 – 2012. Inclusion criteria were a mass removed from 3rd eyelid and at least 1 years follow up information (indirect from veterinarians or owners). Excision was classified as complete or partial. Signalment, eye involved, duration, prior treatment, post-operative chemotherapy and histopathological parameters were analysed. Topical application of 1% 5 – fluorouracil and 0.04% mitomycin-C ophthalmic ointment was performed based on clinician preference. Histopathology was classified for diagnosis and to evaluate surgical margins (pos/neg) and vascular invasion (yes/no). In patients with ocular SCC a surgical margin of 2-3mm is recommended.

Fifty horses were included: 54% male and 46% female. Draft horses were overrepresented (16% in study group vs 2.7% in general hospital population), half of these draft horses were Belgians, thus SCC was probably related to reduced pigmentation.

What they found:

Neoplasia was confirmed in 45 horses (90%) : SCC in 37, lymphosma in 5 and sarcoma, haemangiosarcoma and adenosarcoma in one horse each. Nonneoplastic lesions included epithelial dysplasia in 2 horses, one of which developed SCC one year later, conjunctivitis in 2 horses and adipose tissue in 1 horse.

Recurrence rate was 19% (7 of 37) in horses with SCC and 20% (1 of 5) in horses with lymphoma and one horse with epithelial dysplasia and 1 horse with sarcoma initially diagnosed. The mean duration before recurrence was 2.25 years (median 1.5 yrs) post excision. Recurrence resulted in euthanasia in 6 of 10 horses. A negative outcome was significantly associated (p=0.007) with partial excision of the third eyelid prior to referral.

Type of excision performed at the University hospital was not significantly associated with recurrence (p=0.21), neither were positive margins (p=0.27) or vascular invasion (p=0.25).

Cancer returned in 3 of 19 horses (16%) where no topical therapy was used, in 0 of 5 horses in with mitomycin C was used and 6 of 25 horses (24%) where 5-fluorouracil was used. The use of topical chemotherapeutics was not associated with recurrence (p=0.3). However it must be noted that Mitomycin- C performed well in the small group in which it was used. There was no difference in outcome is surgery was performed on a standing sedated horse or on a horse under full GA. Animals with extensive lesions remain candidates for GA.

Take home message

It is the authors opinion that complete removal of the nicititaing membrane should be performed in all cases because of low risks and increased likelihood of removing the entire neoplasm. This view is supported by the finding that partial excision of mass prior to referral had a significant negative effect on outcome. The prolongerd period in which recurrence was seen (< 2yrs) emphasized the importance of long term monitoring.

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