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A 12-year-old, spayed, female Yorkshire terrier was referred to the ophthalmology service at the Western College of Veterinary Medicine for evaluation of a black mass on the lower left eyelid margin (Figure 1). The menace responses, and the palpebral, direct and consensual pupillary light, and oculocephalic reflexes were present in both eyes. Schirmer tear test (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) values were within normal reference ranges in both eyes. The intraocular pressures were estimated with a rebound tonometer (Tonovet, Tiolat Oy, Helsinki, Finland) and were 16 and 21 mmHg in the right and left eyes, respectively. The pupils were dilated with tropicamide (Mydriacyl; Alcon Canada, Mississauga, Ontario). Biomicroscopic examination (Osram 64222; Carl Zeiss Canada, Don Mills, Ontario) did not reveal any significant anterior segment abnormalities. Examination of the posterior segments of both globes with an indirect ophthalmoscope (Heine Omega 200; Heine Instruments Canada, Kitchener, Ontario) also failed to identify any posterior segment abnormalities.
Our diagnosis was eyelid skin melanoma. The differential diagnoses include a pigmented papilloma, or a tarsal gland adenoma that has extended through the eyelid, or a partially engorged tick. The latter was excluded based on the physical examination. Tarsal gland adenomas originate from the tarsal glands and usually grow under the palpebral conjunctiva and often extend out of the eyelid margin along the tarsal gland ducts. This pigmented tumor is pedunculated and arises from the eyelid skin and is most consistent in appearance with a melanoma.
Eyelid melanomas are usually benign as are papillomas and tarsal gland adenomas. Surgical removal (excisional biopsy) is a reasonable therapeutic diagnostic option in this dog. Similarly, photographing the lesion and re-examination of the tumor every 6 to 12 mo is also acceptable.
We advised an excisional biopsy after a routine diagnostic database [complete blood (cell) count, urinalysis, serum biochemical profile] was completed and the results were determined to be within normal reference ranges. A routine pre-anaesthetic sedation was completed and general anesthesia was induced and maintained to allow the excisional biopsy. The skin incision was closed with a simple interrupted non-absorbable suture and the dog recovered without complication. The tumor was fixed in 10% buffered formaldehyde, then sectioned and paraffin embedded. Routine light microscopic examination of hematoxylin and eosin stained sections confirmed the diagnosis of an eyelid melanoma. Mitotic figures and subcutaneous invasion were not evident and the morphologic diagnosis was benign eyelid skin melanoma. No complications were noted and a re-examination in 6 mo confirmed no recurrence. The prognosis for the eyelid and eye and the life of the dog is excellent.
Melanomas that arise from pigmented ocular and periocular tissues are a diverse group of neoplasms (1–3). Some have malignancy potential (conjunctival melanoma in dogs and cats, diffuse iris melanoma of cats), while most are benign (limbal melanoma, eyelid skin melanomas, and uveal melanomas). Most, if not all, melanomas that arise from eyelid skin are benign (1,3). The light microscopic examination of this melanoma revealed a benign population of pigmented melanocytes that extended out from the epidermis and surrounded a fibrous and vascular core which is consistent with previous reports of these neoplasms (1–3).
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