Microscopy session March 2016

Today we looked at some cases with Simon, a veterinary pathologist from the Royal Veterinary College, Alejandro, who is visiting Simon from Gran Canaria, and Guy, one of the ophthalmologists from Moorfields. Alejandro has a particular interest in tumours, so that’s what we concentrated on. As an aside, cancer cases are a minority of my workload in terms of numbers – around 10% of my cases. Here are a few of the cases we looked at together.

Cases 1 and 2 were very similar, and were exenteration specimens that had been sent to us by Dr Mark Wood when he did some work in the Congo recently.

In Case 1, the interior of the globe (bottom right) and the surrounding orbital tissue (top left) both contain tumour. They are only separated by a narrow band of pigmented cells – probably retinal pigment epithelium – with some scleral collagen towards the bottom.

In case 2, the sclera can be seen more easily, and the presence of pigment helps us identify choroid and iris. The globe has been breached and is open anteriorly (towards the top). The higher power view reveals keratinisation along with areas of intense inflammation and an occasional squamous pearl.

Both of these cases have extensive squamous carcinoma with involvement of the globe as well as the orbital tissues. It is likely that the origin is conjunctival, but the tumour is so extensive it is difficult to be certain.

Case 3 was an enucleation specimen.

This photo demonstrates a melanoma within the choroid, with a nodule of extrascleral extension (inked green as it was visible on macroscopic examination). A small deposit of tumour is also present within the sclera.

Moving anteriorly, there is tumour within the ciliary body, extending into the trabecular meshwork and into the iris, also forming a coating of the iris surface. Note the little balls of tumour cells scattered across the posterior cornea.

Case 4 is a conjunctival biopsy.

Here, there is a sheet of large atypical cells with little cytoplasm and large irregular nuclei with visible nucleoli. The differential diagnosis can be wide in such cases, but immunohistochemistry usually allows a diagnosis to be made. In this case the immuno profile was consistent with a diffuse large B-cell lymphoma.

Simon and I had quite an interesting discussion on differences in our use of immunohistochemistry. For me, if a diagnosis is not very obvious on initial examination of the H&E stained slides, I use a fairly wide immuno panel straight off, in the expectation that several immunos will turn out to be negative and help exclude certain diagnoses. This allows me to reach a final diagnosis relatively quickly, but I can end up using some immunos that in retrospect weren’t useful for a particular case, which one might criticise as unnecessary use of resources. In contrast, Simon (whose patients’ care costs are met by their owners) has a more incremental approach, and he might start off by picking one or two immunos that he thinks most likely to be positive. If they are negative, he might do the next most likely couple on his list and so on. This way he minimises immuno use (and therefore cost), but it can take longer to achieve a diagnosis.

I’m already booked for a couple of hospital teaching sessions in April, so might not run another multiheader microscope session until May, but I’ll post some highlights of my other teaching sessions before that. I hope to see some of you next time!