Thsi ten year old labrador has gone gradually blind and shows no ocular signs apart from possible changes in the optic nerve as here. She is polydipsic and polyphagic and has abnormally high cortisol levels after an ACTH stimulation test but a normal reduction after a low dose dexamthasone test. What might the cause of the blindness be and is it reflected in the appearance of the optic nerve?
Here is an MRI picture with gadolinium enchancement showing a pituitary chromophobe macroadenoma with surrounding oedema (the big white circle in the centre of the image for those of you as clueless about radiology as I am!) which is causing pituitary-dependent hyperadrenocorticism and pushing down on the optic chiasm too resulting in the blindness. Radiotherapy gave back some vision for 6 months but eventually blindness returned. The big question is whether the optic nerve is showing any swelling – papilloedema. You could convince yourself that it is, knowing the results of the MRI but I’m not so sure – what do you think?