A quieter session this month, which just meant more mince pies for everyone who attended.
We started with a review of corneal structure, and had a chat about the phenomenon of Descemet’s membrane thickening during endothelial cell loss. Charlotte raised a very interesting question as to the relationship of thickened Descemet’s membrane to corneal oedema. My simplistic understanding is:
- Endothelial cells have a function of keeping the corneal stroma dehydrated. They also produce Descemet’s membrane.
- When endothelial cell density (or function) is reduced, the stroma becomes oedematous.
- Endothelial cells don’t regenerate.
- Endothelial cells may respond to an insult by producing more Descemet’s membrane.
- If endothelial cells are lost slowly (eg in chronic disease such as Fuchs’ dystrophy), they may produce excessive Descemet’s membrane, which can become very thick
- However, if endothelial cells are lost acutely (eg in acute glaucoma), the endothelium “doesn’t have time” to produce more Descemet’s.
- Descemet’s membrane doesn’t become thinner: it’s permanent.
- So, in later stage corneal disease, Descemet’s membrane may be of normal thickness or markedly thickened. Either may be associated with few or no endothelial cells and with corneal oedema.
I hope that makes sense. I don’t think I’ve specifically read references about this. Please let me know if you believe my reasoning to be wrong, or if you can recommend any references about this!
Now for a few cases that we discussed.
This is one of the commoner eyelid biopsies we receive in the Department of Eye Pathology.
The low power view shows tarsal tissue with meibomian (sebaceous) glands. There are optically empty spaces in the upper part of the specimen, easily visible even at this power.
The cellularity is “busy”, suggesting maybe an inflammatory infiltrate, particularly to the right.
A higher power view shows multinucleate giant cells. Note how the nuclei are clustered with some overlap. This type of giant cell is often seen with foreign body reaction. Additionally, there are epithelioid histiocytes with oval or slipper-shaped nuclei, consistent with a granulomatous component to the inflammation. The empty spaces are consistent with lipid.
This is a chalazion.
In contrast, this is a skin biopsy.
There is a cellular infiltrate with a mixture of histiocytes and lymphocytes. There are also multinucleate giant cells. In this case, the giant cell nuclei form a ring- or wreath-like structure, with cytoplasmic pallor towards the cell periphery. These are Touton giant cells.
This is xanthogranuloma.
Last case for the month was material removed from the canaliculus at a 3-snip procedure.
Here’s some background info on 3-snip and its indications.
Low power of the H&E-stained slide shows an aggregate of basophilic material with a slightly granular texture with no identifiable tissue. There is a light coating of inflammatory cells on the surface.
Gram stain at medium power shows pronounced positivity (blue). Even at this power, there is an impression of strand-like structures.
At higher power still, we can see distinct filamentous bacilli. This is Actinomyces (I was taught to report them as “Actinomyces-like organisms” though things may have changed since then).
The overall diagnosis is of a dacrylith (stone within the lacrimal drainage system).
That’s all for this month. Next session will be on January 16th. All the best for the festive season.