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The General Practitioner's Approach to Cytology

Updated: Apr 27

I love cytology. But I'm not a specialist in the area.

I always tell my clients that my goal is to acquire a diagnostic sample. A sample that, with the clinical picture, a clinical pathologist can make a diagnosis, or at least a best guess answer to the problem.

There are some that are quick and easy, and in fact, I tend not to stain them or send them now because they wash off the slide. These would be lipomas. But some of the suspected lipomas will have something cellular on the slide, and if I can't recognize the cells, it gets sent away.

Many folks take a wait and see approach, and some will sample everything. I am somewhere in the middle. A fine needle aspiration (FNA) is a non-invasive way to get a few answers, that does not require any sedation or anesthesia, and well, if it can save a life, it is worth it.

I personally use a 25g hypodermic needle, and depending on the feel of the mass, I may redirect the needle 20 times. If the mass is cystic, has a fluid pocket, then I will aspirate with the syringe attached, but otherwise, I don't attach the syringe until the sample is in the needle. I learnt that technique from an intern in my 4th year, as she had an interest in oncology and has since gone on to be an oncologist. But no one really taught me how to collect an FNA sample!

I collect enough samples that I have multiple slides per site. I like to stain some in clinic for various reasons including my own curiosity and learning. Some of the pathology labs take photos of the cells and send them back to you, others do not. So I have gotten into a habit now of staining a slide with diff quik and cruising around the slide and taking a few of my own photos through the microscope using my cellphone camera, nothing fancy. This helps me build a library of slide examples. But the pathologist will prefer if you also send unstained slides, as then they can use their own stains to identify cells.

So, once I have redirected the needle multiple times and I am ready to put the sample on a slide, I use a 3 cc lure lock syringe, fill it with a couple mls of air, attach the needle, and give the plunger a squeeze to push the contents into the slide. I say lure lock syringe, as I have accidentally used a non-lure lock and fired a needle across the room. Not good! Also note, when you are putting sample into the slide, try to figure out where the frosted side is first, otherwise, it will be confusing for the person staining and interpreting the slide. Just a few little tips as I have made these mistakes myself.

After staining, when you are looking at a slide, you want to be able to determine if this is an inflammatory, is it septic, or is it neoplasia. Many times I get hemodilution, a little bit of peripheral blood in the sample, so then you need to decipher if this is peripheral blood contamination in your sample, or is the sample from the mass itself.

One of the best resources for cytology is the Clinical Pathology from Cornell. Here's the information on Sample Collection.

My least favourite diagnosis is no diagnosis at all. The infamous "inconclusive" result. I hate that!

There are some cells that are easily recognizable, and others that are not. Below, you see some cells without nuclei, and occasionally a cell with a nuclei. The cells have distinct borders. Cells that do not have a nuclei are essentially dead cells - flattened, flaky cells that are typical of superficial skin - keratinized epithelial cells. Just a normal finding on skin, in this case we were checking to see if the skin was also infected.

These cells below are a little bit more difficult to recognize, likely because of the smear. The nuclei appear to have multiple lobes. These were neutrophils - called suppurative inflammation. But you can also see bacteria if you zoom in. This was an abscess on the back of a dog.

Then there are going to be cells that you can't really recognize. So you have to discern, if this from an epithelial, mesenchymal or round cell origin? For description of these, head over the the EClinPath site!

The cells on the left are difficult to assess because the cell borders are missing, but the cells on the right are closely adhered, which I put in the category of epithelial. After that, I defer to the clinical pathologist for my answers! This one came back as a perianal adenoma.

After you have a diagnosis, in order to help with determining if you need wide margins, its good to have a biopsy. Some of them you can do excisional biopsies on. If it fits in a skin biopsy punch, go for it, it is a very quick procedure. But in the case of the perianal adenoma, it is much larger than the skin biopsy. Some pathologist will prefer a tru-cut biopsy, as you can get a core sample, but similar to doing your fine needle aspirates, you will want to take several samples, otherwise, they may not make the diagnosis. Then you are left cursing, having to call the owner with the "inconclusive" results. Bummer.

A few years ago, I did a tru-cut biopsy on a firm mass within a large lipoma that came back as a mast cell tumor, so you really don't know what you're getting into if you don't have a biopsy. While I prefer a biopsy before removing a mass, you do not always get the option. Sometimes you're asked to remove a lump while the pet is anesthetized for another reason, like a dental cleaning. Obviously, be mindful of what you are comfortable with. I have said, this is a great time for a biopsy, while they are sleeping, but you will gain confidence as time goes on.

Don't forget that you can always offer owners a referral. If you let the owners have a choice, say hey, this could be really scary, and there is a possibility that I may not remove it all, did you want to see a specialist? Then they understand that there are always limitations to what the naked eye can see. If they don't wish to be referred, likely due to costs, then at least they have been informed.

A Lesson Learned Too Late

There is one mass in particular that I had wished I had aspirated. Lesson learned too late. I was a new graduate as the second doctor in a two doctor practice. I had a patient come in with a interdigital cyst. Typically these are furunculosis, a reaction of the skin cells to the keratin, I usually explain it to owners like an ingrown hair. It's an inflammatory process, which usually responds to anti-inflammatory medication. This cyst was about the width of my thumb nail. I had my mentor have a look at it, I spoke about doing an FNA on it, and he said it likely wouldn't be useful, and I could poke it, but it was going to bleed everywhere. I spoke to the owner and mentioned this, and we decided to try a topical anti-inflammatory gel. A few weeks later, the dog has come back because the cyst still had not resolved, and now it was bigger. This time we tried an oral anti-inflammatory. A few weeks later, and this cyst still hadn't resolved, but this time it had burst and the owner described it like a piece of pepperoni. Eventually, we took a cell sample, and found out it was a mast cell tumor. The patient required a toe amputation to have this tumor removed. So in hindsight, I wish I had aspirated this cyst sooner! By the time we had removed the toe, it had already spread to the draining lymph nodes, and eventually to the lungs.

I tell this story because I want you, the new graduate, to stick to your schooling, aspirate anything you want to aspirate. You never know who you will end up saving.

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