Microscopy October 2017

In this month’s session we welcomed back Simon and Alejandro from the Royal Veterinary College as well as Institute of Ophthalmology researchers Alison, Beatriz and Karla.
We started with a case of Reis-Bücklers corneal dystrophy, which led to a chat about granular dystrophy variants and other TGFBI-associated dystrophies. Other cases included eye trauma and intraocular cytology.
We finished up with a couple of veterinary cases – thanks, Simon! These were the wonderfully named spindle cell tumour of the iris in blue-eyed dogs and an unusual case of ocular protothecosis, which is an infection which typically affects the gut rather than the eye.
Here are a few highlights.

Case 1
Corneal graft

Cornea low power

On low power, this cornea is markedly abnormal. There is peripheral scarring reflecting previous surgery (in this case, multiple corneal grafts). In the top right of the field there is vascularisation and inflammation, and melanin pigment within the posterior stroma. Towards the bottom left the stroma is devitalised – it is uniformly pale and keratocyte nuclei are not visible.

Cornea high power

This higher power view of the posterior stroma and Descemet’s membrane shows a chronic inflammatory infiltrate and melanin pigment. Within the stroma are also cystic structures…

Cornea high power (annotated)

I’ve highlighted some (but not all) of them here

Cornea, Acanthamoeba IHC

Unsurprisingly, Acanthamoeba immunohistochemistry is positive.

This patient has had extensive medical and surgical treatment for persisting Acanthamoeba keratitis.

Case 2
Conjunctival biopsy

Conjunctiva low power

In this biopsy, the conjunctival surface epithelium is on the right with the base (inked green) on the top left. The epithelium is flattened with discohesion. Within the stroma is a cellular infiltrate. Although some of the infiltrate is inflammatory (especially towards the lower edge of the picture) most of it is tumour. There are two patterns to the infitrate.

Conjunctiva low power (annotated)

On the right (blue rectangle) is a single-cell infiltrate that might be described as “Indian file”.
On the left (green ellipse) the cells have a more nested architecture and focal melanin pigmentation.

Conjunctiva high power

This higher power view shows nesting on the left, with moderate and focally marked nuclear pleomorphism. Small nucleoli are visible although there are no definite mitoses in this field. A few lymphocytes and plasma cells are on the right, close to blood vessels.

This is malignant melanoma.

Case 3
This is another conjunctival melanoma.

Conjunctiva low power

This low power view shows largely denuded and flattened surface epithelium, partly lifted off by atypical melanocytes, particularly to the left of the image. Within the stroma towards the top right, atypical cells infiltrate the subepithelial stroma, along with inflammatory cells. In contrast to the previous case, there is neither nesting nor an “Indian file” appearance.

Conjunctiva high power

Higher power shows cells with scanty cytoplasm and moderate nuclear pleomorphism. These nuclei are hyperchromatic (dark) compared to those in the previous case.

Conjunctiva MelanA IHC (red)

MelanA immunohistochemistry (positive cells are red) confirms the extent of the infiltration. An intraepithelial component is seen towarrds the left, while the rest is invasive melanoma.

Case 4
Conjunctival biopsy with yet another malignant melanoma.

Low power of conjunctiva

The low power shows this tumour to have a rather confluent architecture of atypical melanocytes within the stroma, with a minor intraepithelial component (particularly noticeable in the lower left of the image).

High power of conjunctiva

Higher power shows two mitoses within the field. I included this case because I don’t find stromal mitoses in conjunctival melanoma very often, and this is a particularly good example.

Case 5
This is a piece of skin from a patient with a pigmented patch

Skin low power

An incidental cyst is present towards the top. In the basal epithelium there is increased melanin pigmentation associated with a proliferation of atypical melanocytes. The appearance is quite subtle.

Skin high power

Higher power demonstrates the atypical melanocytes. They have hyperchromatic (dark) angulated nuclei and little cytoplasm. Not all of the melanin is within melanocytes, and there may be an element of pigment incontinence.

Skin, MelanA IHC

MelanA immunohistochemistry (performed in red so as not to be confused with the background melanin pigmentation) demonstrates a confluent proliferation of melanocytes, largely limited to the basal epithelium.

This is lentigo maligna. There is no evidence of invasive melanoma here.

In the Department of Eye Pathology, we very rarely see skin specimens with lentigo maligna (or even any cutaneous melanoma) although conjunctival melanoma and melanosis with atypia is quite common. Of course, dermatopathology departments will see plenty of these cases in routine practice.

That’s it for this month. My next multiheader session will be on Thursday 16 November. Don’t forget, registrations are also open for the British Association for Ophthalmic Pathology meeting which I’m hosting in London on 12-13 April 2018.

BAOP link

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