Conjunctival Melanoma in a Horse Treated by Tumor Resection and Cryotherapy

Abstract

Background: Ocular melanoma is very rare compared to cutaneous melanoma in horses. Definitive diagnosis is made through histopathological examination and treatment options include surgical excision associated with cryotherapy, radiation therapy, and chemotherapy. In this report, we describe a case of conjunctival melanoma in a horse that has been treated successfully with surgical excision associated with cryotherapy. Case: A 15-year-old male Percheron male was referred to the Ophthalmology Veterinary Section of the Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil, with a history of a pigmented mass located on the lower eyelid of the left eye. Ophthalmologic examination revealed ocular discomfort, secretion and a pigmented mass in the left inferior bulbar conjunctiva. The dermatological examination revealed other melanomas in the perineal region. Complete blood count and serum chemistry profile were within normal ranges and prior to surgery the horse was treated with flunixin meglumine (1.1 mg/kg, IV, q 12 h). Sedation was performed with xylazine (0.4 mg/kg, IV) and detomidine hydrochloride (0.01 mg/kg, IV) and then the animal was placed in a retention trunk. The conjunctival mass was resected with a margin of safety. Liquid nitrogen was applied to the tumor site and the adjacent conjunctiva with a copper cryoprobe with one unit of liquid nitrogen. Histopathological examination revealed neoplastic cells containing pigmented melanocytes in the conjunctival submucosa, confirming the diagnosis of conjunctival melanoma. Postoperative treatment was performed with flunixin meglumine (1.1 mg/kg, IV, q 12 h) for 3 days and topical ophthalmic ointment containing neomycin, polymyxin B sulfate and dexamethasone twice daily for one week. Seven days after surgery, the lesion was healed. The patient was followed for 24 months after excision and there was no evidence of recurrence. Discussion: Older horses are considered more predisposed to melanoma development, possibly because of the proliferation of melanocytes as a manifestation of aging, and in addition, cutaneous melanomas are common in gray horses and rare in other horse colors. In this case, the horse was a 15-year-old Percheron horse with gray hair. In horses, there is only one case of conjunctival melanoma documented in the literature. In both cases, the ophthalmic examination revealed a large, raised, heavily pigmented mass protruding from the bulbar conjunctiva. The only difference is that in the present case the location of the mass was in the inferior bulbar conjunctiva and in the case cited in the literature. The mass was located in the bulbar conjunctiva under the lateral comer. In this case, the diagnosis of conjunctive melanoma was based on clinical signs and confirmed by histopathological examination. It was decided to perform an excisional biopsy for treatment and to confirm the diagnosis of conjunctival melanoma. The choice of treatment depends very much on the clinical presentation, that in this animal, despite the neoplasia being exte...

Reconstructive blepharoplasty following eyelid melanoma excision using a sliding skin flap in six horses

“…Melanoma of the conjunctiva (Hamor et al, 1997; Moore et al, 2000; Tadeu Pigatto et al, 2018) and third eyelid (Albanese et al, 2015) have occasionally been reported, but the eyelids are more commonly affected. Differentials for eyelid tumours include squamous cell carcinoma, equine sarcoid and lymphoma, among others (Giuliano, 2010; Steinmetz et al, 2019).…”