Skin and eyelid macroscopy

Following on from a teaching session for Moorfields Eye Hospital ophthalmology trainees, I’m setting down some thoughts here on how to dissect skin and eyelid specimens in the setting of ophthalmic pathology. I’m aiming this information at both ophthalmologists (so they can understand what we do) and for pathologists and biomedical scientists who may dissect such specimens. Specimen handling isn’t difficult, but if you’re not sure where you are or where you are going, it can be confusing.

Disclaimer: This is purely personal opinion and my preference for my personal practice. If you want to use the information as a starting point for your own practice, that’s great. There are other approaches and methods that also work perfectly well, and I am absolutely not suggesting you abandon those and use my approach instead! My words below may sound didactic, but that’s because I don’t want to bloat the entire post with disclaimers and caveats. Please take it as read that I am only describing one set of approaches that happens to work for me.

The examples I provide here are for excision specimens, ie the hope is that the lesion is totally removed. This is in contrast to diagnostic biopsies (eg punch biopsies, incisional biopsies, curettings) where complete excision is not expected. So the surgeon will want to know: 1. What is it? and 2. Is it out? and possibly 3. If it’s not out, where is it not out? (ie where should I take more with repeat surgery?)

Simple, non-orientated skin

This type of specimen doesn’t include eyelid-specific structures such as eyelashes or deeper tissue (eg tarsus). We expect to see some kind of lesion either on the surface or distorting the surface.

“Lesion” is a vague term. Useful descriptive terms in the laboratory could include: nodule, papule, macule.

Here is a resource with a quick recap of terms.

We like measuring things! Specimens will generally be measured in 3 dimensions. Our specimens are small, so we always measure in mm. The lesion is measured in at least 1 dimension (the “maximum” size). Since we assume the surgeon wants to know if excision is complete, we also try to measure the distance from the lesion to the closest surgical margin. These dimensions will be remeasured under the microscope, but knowing the closest surgical margin helps when deciding how to slice the specimen.

Here are a couple of (schematic) videos on how I approach non-orientated skins. The first has an obvious surface nodule while the second is a bit more subtle.

So, we now have a sliced skin specimen. Remember, we’re interested in what it is, how big it is, and how far it is away from the margin, and that’s what we want to see under the microscope. The biomedical scientist embedding these slices will embed them on my cut surface so that what I see under the microscope correlates to what I can see macroscopically.

Sliced schematic piece of skin

Four of these five slices are already placed on the surface we want to embed on. The fifth – the leftmost in this image – has the skin surface facing us, so we’ll want to tip it over so it’s standing on the flat (cut) surface for embedding.

Orientated biopsies

(Or “oriented” biopsies, if you don’t use British English 😛 )

Here’s another schematic video looking at how a surgeon might indicate which way up/down/round a skin specimen is. In most cases, it’s easy to tell where the skin surface is, although it can be difficult if the surface is ulcerated or (more commonly) if there has been recent surgery.

Some very basic orientation terminology (mainly for laboratory staff):
Left and right mean the patient’s left and right. If you need to turn the specimen round and pretend it’s “on you” as the patient, always keep track of where you are. If you draw a diagram, please draw it as if you’re facing the patient.

Superior = upper
Inferior = lower
Superior/inferior may be used in a relative sense (if there are multiple lesions), but “upper” and “lower” are absolute terms for eyelids.

Lateral = temporal, ie in the direction of the ears.
Medial = nasal, ie (surprise!) in the direction of the nose/midline.
These terms are mainly useful if we know the laterality of the specimen (ie whether it’s left or right). Surgeons, please include that information.

If for some reason we can’t orientate the specimen, we can use clock hours to refer to relative location: again, with the patient (or the patient’s skin surface) facing us.

A couple of notes for surgeons: diagrams on the request form are good. I would really appreciate it if you draw them the right way up and not upside down! Orientation sutures are certainly useful, but please remember that every suture traumatises the specimen.

Inking orientated biopsies

Since the surgeon has gone to the trouble of telling us which way round the specimen is, we want to preserve that information on the microscope slides. My approach is to ink the specimen 2 colours. Combining that with one slice per cassette (and knowing which direction the slices go in) will maintain orientation all the way through.

If we ink the specimen 2 colours, I want to see each slice with 2 colours. No point having cassette A1 with a green-inked slice and cassette A2 with a red-inked slice: we should already know which slice is in which cassette.

Schematic skin specimen sliced into 5 pieces

Here’s an example. 5 slices, each with 2 colours of ink. 1 piece per cassette (for simplicity), and we know which direction we’re going in (eg temporal to nasal or nasal to temporal, depending on laterality). At the risk of belabouring the point, the first slice (cassette A1) faces in the opposite direction to the other 4 because we want to embed on my cut surface.

Full-thickness eyelid specimens

My notes above can apply to skin specimens in any laboratory. Full-thickness eyelid specimens have more complex anatomy but should (in theory) be more straightforward to orientate.

We can usually tell which surface of a formalin-fixed, full-thickness eyelid is anterior (skin) and which posterior (tarsal conjunctiva). The conjunctival surface is typically shiny and may have yellowish vertical lines indicating meibomian gland. The free margin (mucocutaneous junction) often has eyelashes. Assuming the surgeon tells us the laterality (left/right) and whether it’s an upper or lower lid, we should know exactly where we are. (Yes, it’s possible to differentiate upper from lower lid just by looking at it, but it’s safer to be given that information.)

Here’s my video on how I approach a full-thickness eyelid.

We can ink the surgical margins. These will be nasal and temporal, and either superior (if it’s a lower lid) or inferior (if it’s an upper lid), ie, the “towards-the-fornix” margin. The free margin isn’t a surgical margin. I used to ink the margins 2 colours, but that’s not necessary, and a single ink works fine. We should know which direction the slices are going in (nasal to temporal or vice versa), and unlike skin, we can tell histologically which directions are superior and inferior.

What we do want to know is whether the end blocks (containing the nasal/temporal margins) are embedded on the pathologist’s cut surface (not a true margin) or the surgeon’s cut surface (the true surgical margin). My preference is to embed on my cut surface.

For a refresher on eyelid histology, have a look at a previous post.

I’ve probably rambled on enough – if you’ve got this far, thank you for your patience! I hope the information is useful. Please let me know in the comments if anything is ambiguous, or if you’d like me to expand on anything.

And remember, this is my approach to specimens. Individual laboratories and pathologists will have their own systems that work for them.

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