Microscopy session May 2016

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.

Low power cornea from a patient with macular dystrophy
Low power cornea from a patient with macular dystrophy

Alcian blue positive subepithelial deposits, also in the stromal interlamellar spaces
Alcian blue positive subepithelial deposits, also in the stromal interlamellar spaces
PAS stain of a macular dystrophy cornea
PAS stain of a macular dystrophy cornea

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…

High power of a corneal biopsy. Unhealthy stroma with rounded structures suggesting cysts
High power of a corneal biopsy. Unhealthy stroma with rounded structures suggesting cysts

But the true story was revealed on the PAS and Grocott stains which showed huge numbers of fungal hyphae and spores.

PAS low power showing spores and hyphae throughout the stroma
PAS low power showing spores and hyphae throughout the stroma
PAS high power, showing the septate structure of the hyphae
PAS high power, showing the septate structure of the hyphae

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.

Low power of an orbital biopsy
Low power view of an orbital biopsy
Low power view of a lacrimal gland nodule
Click here for more detail
This is a tumour with both epithelial and stromal components. The epithelium forms ductal structures with secretions, while the stroma is mainly fibrous with a suggestion of myxoid areas. This is a pleomorphic adenoma.

The final case I’m showing here sparked off considerable discussion of comparative anatomy.

This is a child with a plical mass.

Low power of plical mass
Low power view of 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.

Lacrimal gland within plical tissue
Lacrimal gland within plical tissue
Cartilage within plical tissue
Cartilage within plical tissue

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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.