Dilated left pupil

Re: Dilated left pupil

Laura Marshall — Fri, 07 Mar 2014 17:24:53 GMT

Thank you for that great response! Not the differential I was hoping to hear, but will discuss referral for advanced imaging with his owners. When the third eyelid came across, this was straight after the pilocarpine test, so I put it down to that as it resolved. I'll post any updates/further answers. Thanks again, Laura

Re: Dilated left pupil

Mark Lowrie — Fri, 07 Mar 2014 16:13:24 GMT

Your findings, just as you say, are consistent with a lesion affecting the parasympathetic supply to the left eye (parasympathetic component of oculomotor nerve CN III). Sometimes this is referred to as internal ophthalmoplegia.

It would seem most likely that your dog has a tumour of the oculomotor nerve – usually these are small tumours of the nerve at the level of the middle cranial fossa. However, these tumours are usually very small and rarely affect brain function to a point that may lead to euthanasia. We occasionally do follow-up MRI in these patients and they seem to grow very slowly.

Having said this, old text books refer to a cavernous sinus syndrome (CSS). The cavernous sinus is a paired venous sinus that runs along the floor of the middle cranial fossa. CSS or ‘middle cranial fossa syndrome’ (as it is probably better referred to) is characterised by variable involvement of multiple cranial nerves including the oculomotor nerve (CN III), the trochlear nerve (CN IV), the abducens nerve (CN VI), the maxillary and ophthalmic branches of the trigeminal nerve (CN V) and the sympathetic supply to the eye. Internal ophthalmoplegia is the most common presentation of CSS. The reason I mention this is it would be worth assessing the function of these other nerves (see details below) as a means to monitor progression if MRI investigation is not possible. CSS is not a diagnosis but a neurolocalisation and anything can cause it but most commonly it is associated with some form of tumour either primary or secondary. Depending on the type of tumour signs may be slowly or rapidly progressive.

Assessing CN IV and VI – ensure the dog has normal vestibular eye movements, i.e. move the head from side to side to see if normal physiological nystagmus can be induced.

Assessing the maxillary and ophthalmic branches of CN V – usually will see a loss of sensation over most of the face and around the eyes so the palpebral response may diminish.

Assessing sympathetic supply to the eye – this would be signs of Horner syndrome. You mention the third eyelid coming across once but I would only be concerned if this became more persistent.

Re: Dilated left pupil

Kirsten Simpson — Fri, 07 Mar 2014 09:19:54 GMT

I had a cat with similar History. Referrd to the local Vet School Opthalmologist who localised the lesion and it had an MRI scan which showed a tumour in that area plus primary in her kidneys - lymphoma! Doesn't necessarily mean that in this case but check for other weirder things!

Re: Dilated left pupil

Laura Marshall — Wed, 05 Mar 2014 20:17:32 GMT

I'm actually not sure if the right pupil dilates any further in the dark, the left one can't dilate any further I don't think! I can check this though.

Re: Dilated left pupil

Anthony Dennison — Wed, 05 Mar 2014 17:17:22 GMT

Sorry if this sounds like a stupid question, does the right pupil dilate further when in a darkened room, or just constrict whilst testing the PLR and go back to previous size?

Re: Dilated left pupil

Laura Marshall — Wed, 05 Mar 2014 13:56:07 GMT

Sorry, it seems to have removed all my paragraphs and lumped it into a giant block of text...