For this month’s teaching session, we welcomed Hannah and Charlotte back from the Royal Veterinary College, Christiane who is doing a PhD here, and Didi the ocular oncologist. Congratulations, Charlotte, for passing your Board exams!
The slides we viewed were a mixed bag of FRCOphth exam-type cases, including cornea, conjunctiva and orbial biopsies.
Last month I had shown a cornea with macular dystrophy, with a rather unimpressive Alcian blue pattern. These dystrophies are quite rare – on average we only get 4-6 specimens per year so it’s difficult to get a really good textbook case for teaching. It so happened I saw a much better example a couple of days ago, so here it is.
Interestingly, the PAS stain demonstrated numerous guttae which I think in this context may be related to the macular dystrophy. Remember, the presence of guttae might not necessarily mean that the patient has Fuchs’ dystrophy if there’s something else going on.
Our next corneal case was a biopsy from a patient with unsuccessfully treated infectious keratitis. I had initially thought I could see stromal cysts and wondered about Acanthamoeba…
But the true story was revealed on the PAS and Grocott stains which showed huge numbers of fungal hyphae and spores.
Moving on to orbital biopsies, we looked at classic exam cases including schwannoma, plexiform neurofibroma and that old favourite, the adenoid cystic carcinoma.
Here’s one of the cases we looked at.
The final case I’m showing here sparked off considerable discussion of comparative anatomy.
This is a child with a plical mass.
As expected for the site, there is conjunctival epithelium on both sides. The stroma consists mainly of fibrofatty tissue. But in one portion there is some lacrimal gland, and in the other a piece of cartilage.
Accessory lacrimal gland can be present at various sites, but the cartilage is very unusual. In this case, I’ve opted for a diagnosis of complex choristoma (dermoid), although one might argue that it’s just a (rare) variant of normal.
While we were discussing the above case, Charlotte gave us a very interesting overview of the structure of the third eyelid (nictitating membrane) which is present and functional in a number of animal species. In humans, the plica is thought to be a remnant of this structure. The third eyelid in animals can contain cartilage, closely associated with lacrimal-type gland, similar to our human case above.
Another interesting comparative pathology point we touched on was regarding uveal melanomas. In humans, most uveal melanomas are in the choroid (posterior segment) with rare occurrences in the iris. But in cats, they are far more commonly seen in the iris. We’re not sure whether this different distribution in cats reflects actual prevalence, or whether it’s simply that posterior tumours in cats are asymptomatic and therefore not noticed by the owner.
Thanks for everyone who attended for the stimulating discussion! I don’t think I have time to run a June teaching session, so probably see you in July.