Choroidal melanoma presented as glaucoma in a dog: case report and review of the literature

Melanocytic tumours of the choroid are uncommonly diagnosed in dogs. The authors report the clinical findings on a 7-year-old intact male mixed-breed dog that was referred to the Veterinary School of Toulouse for evaluation of vision loss and presumptive glaucoma in the right eye. On examination, corneal oedema, areflexive mydriasis, and cataract were found on this eye. Intraocular pressure (IOP) was 46 mm Hg. As opacification of ocular media precluded adequate visualization of the posterior segment, ultrasonic examination was performed and revealed findings compatible with total retinal detachment and the presence of a surelevated lesion at the posterior pole of the vitreous cavity. A definite diagnosis of the disease process was not made, and the glaucoma was treated medically. Despite medical treatment, the condition worsened and the dog was reexamined two months later because the eye had become painful. IOP in the right eye was 64 mm Hg, and B-scans images showed that the lesion of the posterior pole had significantly enlarged in size. The eye was enucleated, and when the globe was cut in half after fixation, a heavily pigmented mass arising from the choroid of the parapapillary area was observed. Cellular morphology of the melanocytic lesion was compatible with a benign choroidal melanoma. Two years postoperatively, the owner reported no signs of either local recurrence or metastatic disease. We discuss the findings in our case and 22 others previously reported in dogs since 1984, and compare the clinical and histopathologic features to those described for choroidal melanomas in humans.