Microscopy session April 2016

This month, we had 2 returning attendees – Simon from the Royal Veterinary College, and Alejandro all the way from Gran Canaria, plus Sam from our own department. Normally I keep interesting recent cases aside for discussion, but this month was a little different. I had been scheduled to teach the pre-FRCOphth exam trainees a couple of weeks previously, and selected a pile of diagnoses that might come up in the exam. Unfortunately, my session was cancelled due to the junior doctors’ strike, so rather than waste the effort involved in getting the slides out (thanks to Lucretia for pulling the cases!), I reused them for this session. The cases discussed were quite typical examples of their type.

We started off with fairly classic examples of corneal stromal dystrophies – lattice, granular and macular.

Greyish stromal deposits
Greyish stromal deposits

Alcian blue stain
Alcian blue stain

The above is a cornea with macular dystrophy. The Alcian blue stain isn’t as distinctly distributed as you tend to see in textbooks, but as they say “samples don’t read the textbooks”!

Brightly eosinophilic subepithelial deposits
Brightly eosinophilic subepithelial deposits
Masson's trichrome stain
Masson’s trichrome stain

This is granular dystrophy which is recurrent in a penetrating keratoplasty. This explains the rather odd superficial distribution of the deposits which are usually scattered throughout the anterior and mid stroma. The photo below shows the periphery of the specimen, with deposition of the material at the graft:host interface.

Edge of the above specimen
Edge of the above specimen

We had a brief discussion of the TGFB1 (keratoepithelin, BIGH3) gene, and how different mutations can manifest as different corneal dystrophies, sometimes in combination. This includes the subepithelial and anterior stromal dystrophies of Reis-Bucklers and Thiel-Behnke (which I can never spell correctly!). One of the cases we looked at has stromal amyloid deposits (positive for Congo red) and a lumpy dense subepithelial band which is negative for Congo red and Masson’s trichrome. I have therefore called it a combined Thiel-Behnke and lattice dystrophy.

Congo red of combined lattice and Thiel-Behnke dystrophy
Congo red of combined lattice and Thiel-Behnke dystrophy
It's difficult to photograph Congo red under polarisation, but there is a hint of apple green here if you squint
It’s difficult to photograph Congo red under polarisation, but there is a hint of apple green here if you squint

After the dystrophies, we looked at 2 more common indications for corneal grafts as below.

PAS stain
PAS stain
Click here for description and diagnosis
On the PAS stain, you can see irregular epithelium with swollen disrupted stroma. Descemet’s membrane is disrupted and detached with scrolling and some fibrosis (suggesting chronicity). This patient has keratoconus with an episode of acute hydrops
Another case with a PAS stain
Another case with a PAS stain
Click here for description and diagnosis
In this case, the PAS stain is showing Descemet’s membrane. It is of irregular thickness with lamination, and on the posterior (lower in the photo) surface there are buried guttae. This patient has Fuchs’ endothelial dystrophy

Our discussion on genetics issues in corneal dystrophies moved on to a couple of cases with wider systemic genetic implications in the form of phakomatoses – with specific discussion of von Hippel Lindau disease and neurofibromatosis Type I.

Simon had also brought along a couple of slides from calves with congenital cataract. I haven’t paid much attention to cataracts in histopathological terms, since we get very few cataract surgery specimens, and the pathology doesn’t affect patient management. However, in a calf, cataract is of wider interest, since it may be a manifestation of a viral infection which has implications for the whole herd.

Calf lens with wrinkled capsule and Morgagnian globules in cortex
Calf lens with wrinkled capsule and Morgagnian globules in cortex
Calf lens posterior capsule with fibrous plaque - a "posterior subcapsular cataract"
Calf lens posterior capsule with fibrous plaque – a “posterior subcapsular cataract”

Thanks to Simon for providing the photos above and giving us such a good opportunity for discussion.

Next session will be around mid-May – see some of you then!

2 thoughts on “Microscopy session April 2016”

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