Microscopy November 2019

During yesterday’s microscopy session, we chatted about relative frequency of uveal melanoma in humans vs cats and dogs. I didn’t know that certain dog breeds with higher numbers of melanocytes are prone to oral melanomas!

Just came across this recent open access review of canine melanomas as potential models for human melanomas:

Canine Melanomas as Models for Human Melanomas: Clinical, Histological, and Genetic Comparison by Prouteau and André

We also chatted about the use of BAP1 immunohistochemistry in prognostication for (human) uveal melanomas. Interestingly, there’s a recent open access article addressing BAP1 in canine mucosal and uveal melanomas:

Altered Nuclear Expression of the Deubiquitylase BAP1 Cannot be Used as a Prognostic Marker for Canine Melanoma by Jama et al.

Guy, one of the Moorfields Ocular Oncology Fellows, was curious about the occurrence of melanomas in non-UV-exposed sites. Here are a couple of recent open access reviews:

Primary mucosal melanomas: a comprehensive review by Mihaijlovic etc al

Malignant melanoma of sun-protected sites: a review of clinical, histological, and molecular features by Merkel and Gerami

Here are a couple of the cases we examined during the session. I usually post three cases. However, followers of my posts will know that I don’t post anything too uncommon or recognisable: my posts usually focus on what you might encounter in a regular eye pathology practice. Several of yesterday’s cases were so distinctive that I’ve opted to omit them.

Case 1

Evisceration for longstanding retinal detachment, a non-seeing eye and poor cosmesis.

Retina of evisceration specimen

This is disorganised retina with loss of photoreceptor inner and outer segments. In the lower part of the field, there is calcification around a couple of blood vessels. The greyish deposit centrally is calcium oxalate (I’m not 100% sure of this—it might be a different compound).

With polarisation

Here, the deposit polarises nicely.

RPE and choroid

This field shows retinal pigment epithelium, Bruch’s membrane and superficial choroid. (Remember, it’s an evisceration specimen, so structures may be incomplete and disrupted). Of note are the numerous large deposits of eosinophilic material…

PAS on higher power

And these are PAS-positive. This is extensive drusen formation, which I interpret as being a nonspecific reaction to longstanding disease.

Case 2

Corneal specimen

Low power of cornea

This low power view shows us anterior corneal lamella, including the epithelium, Bowman’s layer and partial thickness stroma. The most obvious feature is deposits of eosinophilic material with sharp outlines and of variable size. These are present subepithelially and within the superficial and deeper stroma.

Medium power of cornea

Higher power shows us that Bowman’s layer is partly effaced by the deposits, and there is (unsurprisingly) stromal scarring.

Masson’s trichrome

Masson’s trichrome stain is bright red in the deposit. This is a classic case of granular stromal dystrophy. It is one of the BIGH3-associated corneal dystrophies. The other dystrophies due to mutations in this gene include lattice and Reis-Bücklers (also known as superficial granular).

I’ve previously posted a case of recurrent granular dystrophy in a graft, along with a little more information about the BIGH3-associated dystrophies.

The standard reference for corneal dystrophies is the IC3D (International Committee for Classification of Corneal Dystrophies) classification. This classification is now in its second edition. The second edition is behind a paywall, but the first edition is available open access.

That’s all from me for this month. Next month’s session will be on 11 December, and I expect there will be mince pies.

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