Microscopy October 2018

For this month’s microscopy session, I’d received a request to review FRCOphth examination-type material, particularly corneas. So we spent a bit of time on the three classic corneal stromal dystrophies and their typical (and atypical!) appearances. I have a previous post on the stromal dystrophies here. We also did a refresher on some basic descriptive terms, chatted about corneal genetics and had fun speculating about some oddities.

As a reminder, I don’t post all the cases we discuss on this blog. We usually cover a dozen cases in a session. The ones I post might illustrate a useful feature or lesson, or might be a good example or exam-type case. However, I don’t post the truly remarkable cases. For those, you have to attend in person!

Here are a few of the cases we discussed.

Case 1

Enucleation specimen

Photograph of the (normal-sized) slide.

The slide shows a large intraocular tumour with a collar-stud profile and posterior retinal detachment with subretinal flud. No surprises as to the diagnosis!

High power of tumour

High power shows large discohesive cells consistent with epithelioid melanoma.

Anterior part of globe, low power

The anterior part of the globe (normal cornea, iris and lens are visible) shows tumour in the ciliary body.

When I reported this case, I gave the tumour a TNM category of pT4b pNx pMx. For those of you unfamiliar with TNM (or those who want a reminder), it’s explained in these articles.
This is a patient-friendly article
An overview of cancer staging – general principles
More information about TNM – There’s quite a lot of information in this article, but what I’m talking about in this blog post is mainly covered by section 6. pTNM Pathological Classification

So, for this pT4b case, we have:
pT4b = pathological staging – as opposed to clinical, radiology etc.
pT4b = tumour characteristics – as opposed to nodes or metastases.
pT4b = for ciliary body and choroidal melanomas, there is a chart that assigns tumour sizes (across the base and tumour height) to a value between 1 and 4
pT4b = suffixes a-e are given depending on whether or not the ciliary body is involved and whether there is extrascleral extension

Since I have no information about lymph nodes (N) or metastases (M) I give pNx and pMx (x signifying unknown to me).

Now to the slight complication with this case.

High power of scleral defect

There is a breach in the sclera, where (I presume) fresh tumour was sampled for cytogenetics following the enucleation. Unfortunately, tumour now liberally coats the external aspect of the sclera.

Low power of scleral defect

In the TNM system for uveal melanomas, an extrascleral tumour nodule of >5mm by definition gives the tumour the highest stage: pT4e, no matter the tumour size or whether the ciliary body is involved.

In this case, the extrascleral tumour is obviously artefactual, but if there is genuine extrascleral spread, it would be very difficult to detect. In a proportion of uveal melanomas, extrascleral extension is not detected clinical before surgery. See here for more details (nothing like self-citation!)

Case 2

Here’s a cornea I posted on Twitter a few days ago. It was fun to see (and make) comments, but the case merits a bit more space here.

The clinical diagnosis was of previous herpetic keratitis. There’s plenty to see!

Low power cornea

Low power view shows full thickness cornea. Blue crumbly material just beneath the epithelium (especially towards the R margin) suggests calcium, ie band keratopathy. The stroma has a band of lighter texture. Posteriorly there is vascularisation. Descemet’s membrane is folded.

Mid power cornea

Annotated higher power view helps us appreciate the feathery texture (3) in the stroma. I suspect there has been vascularisation and lipid leakage, giving an appearance of cholesterol clefts. There is also a light inflammatory infiltrate throughout the stroma.

  1. The basal cells of the epithelium are a bit swollen and pale, suggesting oedema
  2. Blue stippling in the region of Bowman’s layer indicates (calcific) band keratopathy, probably secondary to chronic inflammation
  3. Lipid
  4. The deeper stroma is lightly vascularised
  5. Descemet’s membrane is folded (I’ve no idea of the mechanism!) and there are few surviving endothelial cells

Could I diagnose herpetic keratitis from this appearance? I don’t know if I could be certain, but the lipid deposition would make me think of herpes. Somehow (and I don’t have hard evidence for this), the depth of stromal blood vessels also makes me think of herpes rather than, say, bacterial keratitis.

There’s an Open Access paper by Faraj here on clinical evaluation of corneal vascularisation.
And here, Lyall examines outcomes of DALK in HSV-related corneal disease.

Case 3

Final case is a punch biopsy of eyelid

Low power lid biopsy

Low power shows a tumour on the right (no surface epithelium) and a cell cluster with a big hole on the left.

Higher power of lid

Higher power of the tumour shows nests of basaloid cells with occasional squamous eddies. There is peripheral palisading. This would do for a basal cell carcinoma.

Posterior part of lid biopsy

The other part of the specimen shows a collection of epithelioid histiocytes—a granuloma—with associated lipid spaces. There are multinucleate giant cells including a large one lower right. This is a chalazion.

The chalazion might be secondary to the overlying basal cell carcinoma or it might be coincidental. It’s worth bearing in mind that if the histological diagnosis is unexpected, the sample may not represent the major pathology.

Next month’s teaching will be on 7 November. I hope to meet some of you then.

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