An unusual case of ocular melanosis and limbal melanocytoma with benign intraorbital extension in a dog

Abstract

This case report describes concurrent ocular melanosis and limbal melanocytoma in a 6-year-old Golden Retriever dog. Three years prior, the pet was examined for progressive corneal pigmentation and started on topical Tacrolimus but was subsequently lost to followup. Current ophthalmic examination revealed a large pigmented limbal mass and severe corneal pigmentation of the left eye as well as a small focal raised pigmented mass of the right third eyelid. Due to extent and rapidity of tumor growth, the left eye was removed via transconjunctival enucleation and submitted for histopathologic examination. At the time of surgery, numerous orbital structures including intraorbital fat, extraocular muscles, and portions of the proximal nasolacrimal drainage apparatus contained multifocal areas of black pigmentation. These tissues were subsequently removed and submitted for microscopic analysis. The pigmented mass of the right third eyelid was also excised. Histopathology of the left eye and orbital contents revealed a limbal melanocytoma extending to the bulbar conjunctiva and orbital space forming a large, markedly necrotic mass. Diffuse, severe ocular melanosis, abnormal stromal pigmentation of the sclera and orbital tissues, and corneal stromal pigmentation were noted. The mass of the right third eyelid was confirmed to be a conjunctival melanocytoma. To the authors' knowledge, this is the first report of concurrent ocular melanosis and limbal melanocytoma with orbital infiltration. The peculiar multifocal distribution of melanocytes throughout ocular connective tissues may explain the development of multiple melanocytic lesions in this patient.

Canine ocular neoplasia: a review

“…Rare histologically malignant limbal melanomas have been described, and some otherwise benign neoplasms may include areas with cells that are less pigmented or amelanotic and mitotically active. 1,4,8,9,11,12,[42][43][44][45][46][47][48] The immunohistochemical profile of limbal melanocytomas has not been established, but they can be expected to have an immunophenotype similar to melanocytomas at other locations, expressing vimentin, Melan-A, and PNL-2. [17][18][19] The prognosis for life with limbal melanocytic neoplasia is excellent.…”

Third eyelid gland neoplasms of dogs and cats: a retrospective histopathologic study of 145 cases

“…Numerous types of TEL neoplasms have been reported in the veterinary literature including transmissible venereal tumor, squamous cell carcinoma, melanocytoma, melanoma, lymphoma, plasmacytoma, hemangioma, hemangiosarcoma, mast cell tumor, and myoepithelioma in dogs; squamous cell carcinoma, hemangioma, hemangiosarcoma, melanoma, adenocarcinoma, mast cell tumor, and fibrosarcoma in cats; and squamous cell carcinoma, lymphoma, adenocarcinoma, hemangiosarcoma, lymphangiosarcoma, and basal cell tumor in horses . The majority of these neoplasms originate from the surface tissues (conjunctival and lymphoid tissues) or the stroma of the substantia propria . Those that originate in the TEL gland are less common and include adenocarcinoma, adenoma, plasmacytoma, myoepithelioma, and lymphoma .…”

Primary Retrobulbar and Intraocular Malignant Melanoma in a Cat

“…Ocular melanoma results in significant thickening of the uveal structures and anterior sclera due to infiltration by pigment-laden melanocytes, and to a lesser extent melanophages. Secondary glaucoma may subsequently occur due to impedance of the aqueous outflow by pigment (Dees et al, 2013).…”

“…Melan-A is an immunohistochemical marker that has been evaluated in cats on formalin-fixed tissue; it was shown in one report to be positive in 67% of feline melanomas (Ramos-Vara et al, 2002). Immunohistochemistry has shown that the pigment-laden cells in ocular melanoma are usually positive for vimentin, S100, neuron-specific enolase, and Melan-A and negative for cytokeratin (Dees et al, 2013).…”

“…For large intraocular tumors or those with metastatic potential, enucleation may be considered the best option (Dees et al, 2013). Metastatic rates for cutaneous melanomas in cats have been reported to range from 5 to 25% (Patnaik and Mooney, 1988).…”