Microscopy November 2017

For this month’s microscopy session, we welcomed Simon, Alexandro and Oscar from the Royal Veterinary College. Simon kicked off with a couple of dog eyes – a Dobermann with a ciliary body adenoma (which is very rare in humans but not uncommon in dogs), and a Shih Tzu with vitreoretinal abnormalities which are a predilection of the breed. Given the presumed genetic contribution in the Shih Tzu, we had a chat about human familial vitreoretinopathies such as Stickler syndrome. We also chatted about peripheral cystoid retinal degeneration, which is quite often present in the eyes of humans in later life.

Here are a few highlights from the (human!) diagnostic cases for the month.

Case 1
This is an anterior lamellar keratoplasty specimen.

Anterior corneal lamella

There is subepithelial and anterior stromal fibrosis with a distinct break in Bowman’s layer (starred) and modest chronic inflammation within the scarred stroma. Previous Herpes simplex keratitis is a possibility.

Case 2
This is a globe with a melanoma.

Globe melanoma showing ciliary body, angle and iris

The low power view shows tumour within the ciliary body, but not quite extending into the iris. The angle is closed by a fibrovascular membrane – iris rubeosis. Additionally, there are two clusters of cells which catch the eye…

High power view of an odd cluster within the iris

Higher power shows these to be nucleated red blood cells. This is secondary haematopoiesis, presumably because of ischaemia (as is the rubeosis) or maybe tumour-associated.

Intraocular extramedullary haematopoiesis (EMH) is uncommon, and in adults is usually found in intraocular ossification, eg in a phthisical eye or a choroidal osteoma. It can also be found in the context of ischaemia. Since this globe demonstrates iris rubeosis (which I interpreted as secondary to the tumour), ischaemia could be a factor here.

Case 3
This is a biopsy from a slow-growing orbital mass.

Orbital mass

This medium power photomicrograph shows a dense cellular infiltrate of lymphoid cells, lacking germinal centre architecture. The cells are rather small and monotonous.

CD3 immunohistochemistry (brown is positive)

CD3 immunohistochemistry highlights (normal) T lymphocytes.

CD5 immunohistochemistry

CD5 is also positive in normal T lymphocytes, but additionally in certain B cell lymphomas. It is important to assess the CD5 positivity against the background T cells, and in this case there is a clear excess of CD5-positive cells which are not T lymphocytes. The diagnosis here is chronic lymphocytic leukaemia/small lymphocytic lymphoma.

When using immunohistochemistry to evaluate lymphomas and other tumours, histopathologists generally use an immunohistochemistry “panel” rather than a single antibody. Diagnosis is made after assessing the pattern of immunostaining across the whole panel, and it is very rare to make a diagnosis based on a single antibody. For lymphoma diagnosis, our laboratory would typically perform a panel of 12-15 antibodies. If the specimen is small or resources are limited, it is possible to use fewer antibodies and still arrive at a diagnosis, such as in this article.

My next microscopy session will be in January – hope to see you then!


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