Histopaw — What?

What is histopathology and why does your veterinarian recommend it for your pet?

A German Shepherd puppy with it’s head cocked to it’s left.
Photo by Dex Ezekiel on Unsplash

If you’ve ever taken your pet in to have a mass removed, or a biopsy collected you may have heard the word histopathology. What does it mean?

Literally, from its Greek roots, it means ‘tissue disease.’ But it’s really a bit more complex than that. Histopathology refers to the microscopic evaluation of tissues to identify and characterize disease. It can be carried out on tissue samples of almost any size. It is the gold standard (recognized best) for the diagnosis of cancers, auto-immune diseases, and some infectious diseases as well. Colloquially, you’ve probably heard this referred to as, “Sending the biopsy sample to the lab.”

Now, in veterinary medicine, you may have an added reason to care about histopathology. That is, you’ll see it on your invoice or estimate usually for a reasonably large chunk of money.

So, what makes it worth that chunk of money, and why does your veterinarian recommend it?


Doc, why can’t you just remove the mass and be done with it?

The short answer is that I can.

The much longer answer details why I don’t believe that I should.

There are three primary benefits to allowing your veterinarian to submit a sample for histopathology.

Diagnosis

Perhaps the most important aspect of histopathology is that it is the best method available to obtain a definitive diagnosis for most growths and lumps. Your veterinarian submits the mass as a whole, or a wedge from it, and the pathologists can assess what type of cells constitute the growth and whether they are anything to worry about.

Histopathology has a marked benefit over other modalities, such as cytology, because it evaluates full sections of the tissue rather than just a handful of cells. Your veterinarian will make the choice to send a full mass or a section depending on a variety of factors like the overall size, location, and health of the tissue.

Margins

The second major benefit to histopathology is that the sections of tissue that the pathologists evaluate allow them to determine whether the removal was complete. By assessing the margins (or the perimeter) of the mass for normal cells, they can identify whether disease was completely removed, or whether there are expected to be abnormal cells remaining.

This information helps your veterinarian formulate a further plan for your pet. Also, depending on the diagnosis, they may change their recommendation from monitoring the area to repeating a surgery with more aggressive surgical intent. Without this information, there is no way to truly know whether you can just remove a mass and be done with it.

Prognosis

The third benefit to histopathology is that it provides what’s called a histopathologic grade. This grade refers to how aggressive in appearance the cells are under the microscope. There are many cancer types for which there are objective criteria that help the pathologist report a specific level of concern to the primary clinician, or veterinarian.

For instance, in dogs, Soft Tissue Sarcomas are graded on a scale of I-III depending on how they appear under the microscope on histopathology. Grade I tumors tend to be fairly benign, and their cells are more normal in appearance; compared to grade III tumors which tend to be very aggressive composed of highly abnormal and rapidly dividing cells.

The grade can help solidify a decision to remove a mass and forget about it versus needing to consider additional treatments, like chemotherapy or radiation.


Now, as with all things in veterinary medicine, there are many factors that go into the decision to submit for histopathology. In an ideal world, I believe that if we are putting the patient through surgery to remove or biopsy something, we should do our best to confirm what it is and what we need to do next (if anything) — regardless of how benign it seems.

That being said, I work with my clients to meet their goals for their pets. For some owners, removing a mass is simply as far as they wish to go. Their logic follows, “Well if it’s not going to change what I do next, why should we do it?” So, if that’s how they feel, I won’t push them too hard, it’s a fair position for them to be in as long as they recognize that we’ll be blinded to some of the information.

I hope that this article helped to shine some light on what your veterinarian is truly recommending when they send a biopsy off the lab. Thanks for reading!

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