Choroidal Melanoma in a Dog

Abstract

ABSTRACT. A 7-year-old intact female golden Retriever was referred for evaluation of an intraorbital mass of the left eye. Based on ophthalmoscopy, ultrasonography and magnetic resonance imaging (MRI), the tentative diagnosis was made as an intraocular neoplasia, especially choroidal melanoma. The orbital exenteration of the affected eye was performed. The mass was histologically diagnosed as malignant choroidal melanoma. No signs of recurrence and metastasis were detected by thoracic radiographs, blood examinations and MR images, and the dog was clinically healthy for 23 months after operation. KEY WORDS: canine, choroidal melanoma, magnetic resonance imaging (MRI).J. Vet. Med. Sci. 67(8): 821-823, 2005 Melanomas are the most common primary ocular tumor in dogs, although primary ocular tumors are relatively rare [1]. Most of primary melanomas in dogs arise from the anterior uveal tract such as the iris and ciliary body [1,4,11], and primary choroidal melanoma is less common among primary ocular melanomas [2,9]. Previous studies documented 4% of canine ocular melanomas to be of the choroidal origin and the behavioral and cytologic features were benign [3,11]. Another report on benign choroidal melanoma in a dog showed that the tumor lesion did not change for 7 years, similar to that of human uveal nevus [10]. But the other case of canine choroidal melanoma with metastasis was reported [4]. The present paper describes ophthalmoscopy, magnetic resonance imaging (MRI), histopathology and a 23-month follow up of a choroidal melanoma in a dog.A 7-year-old intact female golden Retriever was referred to Veterinary Medical Center (VMC) at the University of Tokyo for evaluation of an intraorbital mass of the left eye. Two months prior to referral, the owner noticed the blindness of the left eye of the dog and admitted to a practitioner. Opthalmic examinations revealed mydriasis and loss of menace reflex and direct pupilary light reflex in the left eye. Consensual pupilary light reflex was lost in the right eye. Then the patient was referred to another practitioner to examine the cause of the vision loss of the left eye, where the black pigmented and edematous retina around the optic nerve disk were found on ophthalmoscopy and diagnosed as inflammation of the nerve disk. The dog was treated with the taper dose of prednisone with an initial dose of 2 mg/kg/ day. Two weeks later, the dog received ophthalmoscopy and was revealed that the edematous area was reduced but the black-pigmented area was enlarged and rose up toward the vitreous. Ultrasonogram of the affected eye revealed the solid mass lesion which overlaying the optic disk area. Then the dog was referred to VMC for the detail evaluation of the solid mass by MRI.On physical examination, the dog was clinically normal. Complete blood count and blood chemistry revealed no abnormal findings. On ophthalmic examination, the menace reflex and the pupilary light reflex were lost as seen in the practitioners. The intraocular pressure was within the normal range in both ey...

Eye

“…67,[69][70][71]74,76,[79][80][81] They include malignant uveal melanomas as well as melanomas of the eyelid, bulbar conjunctiva, and iris. 67,[69][70][71]74,76,[79][80][81] They include malignant uveal melanomas as well as melanomas of the eyelid, bulbar conjunctiva, and iris.…”

Presumed primary uveal melanoma with brain extension in a dog

“…Unlike in human beings, most primary melanocytic tumours in dogs arise from the anterior uveal tract such as the iris and ciliary body (Ryan and Diters 1984, Wilcock and Peiffer 1986, Dubielzig 1990, Collinson and Peiffer 1993, Morgan and Patton 1993, Schoster and others 1993, Miller and Dubielzing 1996, Giuliano and others 1999, Narstrom and Ekesten 1999, Hyman and others 2002, Miwa and others 2005, Donaldson and others 2006, Yi and others 2006), and involvement of the choroid is an extension from the anterior uvea (Yi and others 2006). Thus, many of them, if ignored for long enough, will extend from the base of the iris through the ciliary body and into the choroid, reaching the optic nerve and its meninges.…”

“…In dogs, extension of uveal melanomas through the angular plexus into the sclera or even conjunctiva is very common (Narstrom and Ekesten 1999, Hyman and others 2002). Two cases of choroidal melanoma with infiltration into the rostral portions of the optic nerve have been described in dogs (Schoster and others 1993, Miwa and others 2005), while anterior uveal tumours have not been documented to invade the optic nerve. Invasion into the brain seems to be exceedingly rare in dogs, and to the best of author’s knowledge, this is the first published report.…”

“…Uveal melanocytic tumours are the most common primary intraocular neoplasms in dogs, and both benign melanocytomas and malignant melanomas have predilection for the anterior uveal tract (Ryan and Diters 1984, Dietz and others 1986, Wilcock and Peiffer 1986, Dubielzig 1990, Collinson and Peiffer 1993, Morgan and Patton 1993, Schoster and others 1993, Miller and Dubielzing 1996, Giuliano and others 1999, Narstrom and Ekesten 1999, Rovesti and others 2001, Hyman and others 2002, Wilcock and others 2002, Miwa and others 2005). Involvement of the choroid is considered to be an extension from the affected iris or ciliary body (Yi and others 2006).…”

“…Involvement of the choroid is considered to be an extension from the affected iris or ciliary body (Yi and others 2006). Evidence of metastases or extrascleral extension is rarely reported (Dietz and others 1986, Giuliano and others 1999, Narstrom and Ekesten 1999, Miwa and others 2005), although most melanomas have invaded the sclera at the moment of enucleation (Giuliano and others 1999). However, invasion into the brain has not been previously reported.…”