When the Tests Disagree: The Diagnostic Gap Between Cytology and Histopathology in Canine Splenic Masses

A splenic mass shows up on ultrasound and the question hits like a brick: benign or malignant? We go straight at the uncomfortable truth behind canine splenic cytology. Even when splenic FNA feels like the “do something now” step, the match between cytology and histopathology is only moderate, and that has consequences for how we advise families, schedule rechecks, and decide when splenectomy is the safest path.

We talk with Drs. Janet Grimes and Matthew Aluisio about what their data means in the exam room: why a neoplastic cytology result tends to be more predictive than a non-neoplastic one, and why a benign aspirate does not rule out cancer. We unpack the spleen’s built-in complexity, including extramedullary hematopoiesis, mixed cell populations, and the sampling problem of trying to summarize a large, heterogeneous lesion from a tiny needle sample. We also get specific about the diagnoses no one wants to miss, including hemangiosarcoma and lymphoma, and how tumor exfoliation and overlap with reactive processes can blur the picture.

From there, we shift into action: when cytology is most useful, when serial ultrasound monitoring is a reasonable strategy for smaller, non-ruptured nodules, and when size and rupture risk should move the conversation toward surgery and definitive histopathology. We also dig into the “possibly neoplastic” gray zone and why calling your pathologist can be one of the most practical diagnostic tools you have.

If you work up splenic masses in dogs and want clearer owner conversations, better monitoring plans, and fewer false reassurances, this one is for you. Subscribe, share with a colleague, and leave a rating and review so more clinicians can find the show.

JAVMA article: https://doi.org/10.2460/javma.26.01.0006

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Transcript

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Why Splenic Masses Need Better Answers

Lisa Fortier 0:31

Welcome to Epic Award-winning Veterinary Vertex, the AVMA Journal's podcast where we delve into behind the scenes look with manuscript authors. I'm editor-in-chief Lisa Fortier, joined by Associate Editor Sarah Wright. Today we're discussing how cytology and histopaths have poured a fair agreement on the determination of neoplastic or non-neoplastic lesions in dogs with splenic masses or nodules with Matthew Alusio and repeat guest the spleen clean herself, Janet Grimes.

Sarah Wright 1:01

Thank you for joining us, Matthew and Janet.

Lisa Fortier 1:03

Thanks for having us. We're excited to be here.

SPEAKER_03 1:06

Yes, thank you for having us.

Lisa Fortier 1:08

All right, Matthew, let's start off with you. What clinical problems or misconceptions motivated you to study the agreement between splenic histology and histopathology?

SPEAKER_03 1:18

Splenic masses, they're very common in dogs, and currently the gold standard for a definitive diagnosis is a splenectomy followed by histopathology. We currently do not have a great preoperative diagnostic tool to determine if these masses are benign or malignant. Splenic FNAs are commonly used, but previous literature has a wide range in accuracy between splenic cytology and histopathology, which warranted further investigation. Additionally, all of the previous studies included splenameglia in addition to splenic masses, and some of them included both dogs and cats. The accuracy of cytology for just splenic masses in dogs has had not been reported.

Sarah Wright 2:03

Janet, for listeners who may not routinely manage splenic masses, can you briefly explain the practical differences between cytology and histopathology in this setting? Sure.

Janet Grimes 2:13

So cytology can be very useful because it's minimally invasive. You get an answer pretty quickly. Whereas pathology requires splenectomy, so it's involved, more expensive. You have to pay for surgery as well. And so we often use cytology to get answers for things prior to surgery, but we need to be sure that we're getting accurate answers. And we kind of knew the spleen is one of those areas that we struggle with, whether we can believe it or not. So that's that's kind of how we came about this.

Lisa Fortier 2:44

Yeah, in line with that, Matthew, uh, before conducting the study and while you were designing it, what were your expectations about how closely cytology would align with histopathology?

SPEAKER_03 2:55

Our hypothesis predicted a low correlation between cytology and histopathology. This was mainly based on previous literature and clinical experience, but also on the fact that we were focusing on focal masses for the study instead of uh diffuse splenomegaly.

What 55 To 67% Agreement Means

Sarah Wright 3:13

Matthew, your study found agreement between cytology and histopathology in only 55 to 67% of dogs. What does that level of agreement mean clinically?

SPEAKER_03 3:23

Overall, it means there's poor defair agreement between splenic cytology and histopathology in dogs. Clinically, this reduces the value of cytology as a preoperative diagnostic tool for splinting masses, but does not render it completely useless. We will be discussing where we think cytology is useful soon.

Lisa Fortier 3:43

Yeah, aligned with that, I thought, Janet, one of the most important findings for me in your manuscript was that several lesions were interpreted as a non-neoplastic on cytology, were ultimately neoplastic on histopath. Why is it so challenging to diagnose these lesions cytologically?

Janet Grimes 4:01

Yeah, so I think that's a great question. So cytology is somewhat limited. Um, so you can only assess the area that was sampled. And so with histopath, you have access to the entire lesion. You can go cut in another sample, um, look at a different area of a mass, especially if it's a particularly large mass. Um, and then also some, you know, in many cases we're dealing with more than one nodule or mass. And so trying to correlate the mass that was sampled cytologically with the one that was looked at histopathologically can be difficult. And uh I think also, you know, we don't worry too much about removing the spleen in dogs. We kind of just take it out without a second thought. But the spleen actually does a lot of important things. Um, you know, it filters all of our red blood cells, it contains lymph tissue producing B and T cells, and so there's a lot of activity in the spleen, and hematopoiesis can occur within the spleen, and nodule hyperplasia is pretty

Why Cytology Misses Dangerous Tumors

Janet Grimes 5:02

common in older dogs. And so within all of these nodules that can be normal, uh, many different cell types can be present. And some of these are precursor cells, so precursor erythrocytes or um platelet cells, you know, things like that. And so it it can be difficult to distinguish some of those precursor cells from one another, which also can make it difficult to determine neoplasia from a benign normal process.

Sarah Wright 5:30

I know we're talking today about cytology and histopathology, but I do have to give a shout out, Jant, to your last podcast episode. We were talking about microRNAs too. So for those of you that are listening and want to learn more potentially about what you can do prior to surgery to see potentially outcomes, I would definitely suggest listening to that episode. So now back to cytology and histopathology. Matthew, you found that a neoplastic cytology result was more predictive than a non-neoplastic result. How should clinicians interpret a benign aspirate in practice?

SPEAKER_03 6:01

Yes. Our our study reported that 63% of non-neoplastic cytologic diagnoses were accurate. And given this information, a benign aspirate, it means that a benign aspirate does not rule out neoplasia.

Lisa Fortier 6:15

Wow, that can be confusing. Uh, Janet, were there particular tumor types or lesion characteristics that at least appeared to you to be difficult to classify accurately, I should say, with cytology?

Janet Grimes 6:27

Yeah, so I think that is probably one limitation of the study was having enough of each um tumor type to really make those associations between difficulty. And so, you know, we we kind of expected sarcomas to be difficult to identify with cytology because they just don't exfoliate well. Um, and some, but some of them actually were accurately identified. Um, but for the tumors that pathology identified, that cytology did not, um, those were all a combination of either homangiosarcoma or lymphoma. Um, and so I think that makes sense because again, the sarcoma cells don't exfoliate well. Um, lymphoma also can be really difficult to distinguish from that lymphoid hyperplasia in some in some cases. And so the the clinical pathologist has to look at um multiple different criteria to kind of make that call as to whether it's going to be neoplastic or not. And so sometimes that can be really difficult.

Sarah Wright 7:26

Yeah, it sounds really challenging. And to make things even more challenging, Janet, your study included one case where cytology and histopathology both identified neoplasia but disagreed on tumor type. How does that happen?

Janet Grimes 7:39

That case was really interesting. So, similar to kind of the last question, um, this was a case of lymphoma. And so on the cytology of this case, they saw lymphoid reactivity and sarcoma cells. And so, because I think cancer cells are often mutated, they can have varied appearances and they can look pretty um aggressive or just very abnormal in a sense. And so I think that that contributes to making it difficult to call because we know lymph cells are normal to be there and a lot of them. Um, but if they're bizarre looking or something like that, it's it's just you need to see enough of those features to really say that it's cancer.

When Monitoring Beats Splenectomy

Lisa Fortier 8:22

So if you put all that together, Janet, based on the findings of this manuscript and your own clinical experience, when do you think cytology is most clinically useful when you're working up cases of spunic masses or nodules?

Janet Grimes 8:35

Yeah, so I think it's reasonable for smaller lesions and non-ruptured lesions is kind of what we're talking about here. So I think if you have a smaller lesion, um, I think cytology and active surveillance with serial ultrasounds is reasonable. Um, but you need to be paying attention. So don't just say it's benign and never look again. Um, so we want to get them back in for another ultrasound, see if that nodule is increasing in size. And if it is, then you might eventually lean towards splenectomy if it continues to increase in size. But some of these nodules could stay the same size or decrease in size or disappear. And so those are ones that would be great to avoid, you know, doing a splenectomy on.

Sarah Wright 9:20

Yeah, great clarification. Matthew, how should these results influence discussions with owners about next steps, including surgery, monitoring, or additional diagnostics?

SPEAKER_03 9:31

Yeah, I'd like to split this one up into neoplastic and non-neoplastic situations. For the neoplastic cytologic diagnosis, then further investigation with surgery and histopathology is definitely warranted. If the dog has a non-neoplastic cytologic diagnosis, neoplasia cannot be entirely ruled out, as mentioned before. So there's a few different scenarios. Monitoring, such as serial ultrasounds, is acceptable, especially for smaller nodules. Surgery may also be warranted, especially for larger masses that are at risk of rupturing. And overall, there's not a great straightforward answer for this question or for the situation, which highlights the need for an accurate, more accurate pre-operative diagnostic tool.

Lisa Fortier 10:18

Yeah. I love, Janet, the word uh possibly neoplastic. It sounds so Switzerland for the pathologist. How pathologists approach cases that fall into this diagnostic gray zone, and what do you as a clinician do with that

Talking Through The Gray Zone

Lisa Fortier 10:31

information?

Janet Grimes 10:32

Yeah, so I think it's a difficult scenario, and it really depends on the person reading the slides as well as to how much how much information they need to kind of make that call. Um, and so I think for cytology, we all know the correlation with histopathology is not perfect for the spleen. And so I think there's a tendency not to want to overstate the findings, which I think is reasonable. Um, but as we discussed, there's a lot going on in the spleen, and so it's just really hard to know, you know, what the difference is between neoplastic and non-neoplastic. And so um, since histopathology is the gold standard, I think it's more straightforward for a clinical pathologist to say, we think it could be, but we're not sure. And then they can always recommend removal with histopathology to be certain. Um, and then with histopath, there's so much more of the tissue that can be sampled, and they can use immunohistochemistry as well to help determine kind of cell lineages to make that final cut. I think if I see possibly neoplastic, I'm more concerned about that. And so I definitely want to at a minimum at least keep not monitoring that nodule. Yeah, that makes sense.

Sarah Wright 11:41

I think it's also a really great case, too, to say maybe you could call your pathologist too and even talk to them. I know sometimes you look at the report and they just want to move on, go to the next thing, but I don't think it's ever wrong to just call them and say, hey, like what were you seeing? Like, let's talk more about this.

Janet Grimes 11:53

So yeah, I think I think that's a great point. We really should have more communication, as I agree.

Sarah Wright 12:02

So now we have to talk about some fun things from your study. So we want to know what surprised you. So, Janet, you shared a lot of interesting things, but what is one thing that genuinely surprised you?

Janet Grimes 12:13

Um, I'm not sure that I was totally surprised by anything. Um, I kind of went into this as a surgeon thinking cytology is not very helpful, but I'm also thinking of that scenario where I have a bleeding splenic mass and I'm gonna go to surgery anyway. And so I think obviously for that, we're not usually doing cytology. Um had the anatomic pathologist look at, is you know, a lot of times we'll get a cytologic diagnosis of extramedullary hematopoiesis. Um, and then on pathology, it'll come back as you know, hemangeosarcoma, let's say. But in reality, there probably was extramedullary hematopoiesis also happening. And so that's where, you know, cytology is not lying to you, it just didn't get all of the data, I guess. And so we had our pathologists specifically look for that EMH to see if it was there to kind of just correlate. Is cytology just seeing a different part of this lesion?

Lisa Fortier 13:14

So yeah, Matthew, uh, without the benefit of the uh I'll call it experience of the spleen queen, was there anything in this study that surprised you?

SPEAKER_03 13:26

Yeah, I was surprised with the 63% accuracy of cytology for non-neoplastic lesions. In within these, there was four cases where cytology missed hemangea sarcrama and three cases uh where cytology missed lymphoma, which are both diseases that you don't want to diagnose inaccurately.

Surprises, Next Studies, Closing

SPEAKER_03 13:46

So I was surprised with those results.

Lisa Fortier 13:50

And Matthew, if you could design a study going forward to answer some of these unanswered questions that every study brings up, we just learn more what we don't know. What would you decide to investigate next?

SPEAKER_03 14:01

I have two studies in mind. So with the first one, our study had a low sample size for specific types of neoplasia. Further studies would definitely be needed to correlate the accuracy of cytology and histopathology for specific types of neoplasia. In general, round cell and epithelial tumors should exfoliate better than mesenchymal tumors, which in theory should correlate to a higher agreement between cytology and histopathology for the uh for the highly exfoliative tumors.

Lisa Fortier 14:34

Right.

SPEAKER_03 14:35

And then the second study. So this one focused on splenic masses in dogs. Given the variation in splenic disease between dog and cats, I think there should be further studies are needed to determine the accuracy of splenic cytology in cats.

Sarah Wright 14:51

That's a great idea. Can't lump them all together.

SPEAKER_03 14:54

Yep.

Sarah Wright 14:55

I would love that. My cat has a curled spleen. So at first, her internet is doing ultrasound. He's like, she might have a splenic mask. I was like, no, she's a cat. What does that mean? So then I brought her to my radiologist for my internship, and I was like, Can you please just look at her spleen? He's like, the spleen's just curled. You're okay. I think we still had the cytology and it came back fine, but please look at the cat. I always appreciate that. Well, Matthew and Janet, thank you so much for joining us. I always learn so much about spleens whenever we have you on the podcast. Shout out again to spleen queen, Janet Grimes. We really appreciate you being here.

Janet Grimes 15:26

Thank you all so much. We appreciate your your help getting these this information out there.

SPEAKER_03 15:31

Yes, thank you.

Sarah Wright 15:32

For our listeners and viewers, you can read Matthew and Janet's article in Japan. I'm Sarah Wright here with Lisa FordiA. Be sure to tune in next week for another episode of Veterinary Vertex. And don't forget to leave us a rating and review on Apple Podcasts wherever you listen.