You’re a What? What’s a Pathologist?
by Rebekah Gunn-Christie, DVM, DACVP
A lady at my gym asked me what I do for a living. “I’m a veterinary pathologist,” I said and then paused, smiling, as I waited for the inevitable furrowing of brows and subsequent barrage of questions about my line of work. “You’re a…what?” she asked, her voice trailing off at the unexpected constellation of words I had concocted. “I’m a veterinary pathologist,” I repeated, more slowly. “I evaluate and interpret pathology specimens.” The brows relaxed, slightly, but I could tell she was still perplexed. I volunteered a slightly longer explanation: “I went to veterinary school, and then I completed a residency in pathology. Now I look at cytology cases (sometimes called needle biopsies) for a diagnostic lab.” “Oh,” she said, understanding more but still not enough to really know how I play a role in keeping pets healthy.
This is the norm for me when I try to explain what I do to those who aren’t in the medical field or have been lucky enough not to have needed the services of a pathologist. I was once one of those confused question-askers. My half-sister’s stepfather is a pathologist. As a child, and already dreaming of becoming a veterinarian when I grew up, I was thrilled to discover that I already had a family member who was a veterinarian. Wowee! Someone on the inside, to whom I could ask questions and get a leg up on my learning! But my enthusiasm was rapidly curtailed when I learned he didn’t actually work with animals. Wait — what? A veterinarian who doesn’t practice on animals? It wasn’t until an embarrassing number of years later, when I put two and two together, that I realized exactly what this vet who didn’t deliver calves, examine puppies or kittens, do surgery or give vaccines did for a living. And then I went to veterinary school and found out it was my calling, too.
After veterinary school, I completed the standard three-year residency in pathology, which is the study of disease. I also earned the fancy title of “Diplomate, American College of Veterinary Pathologists” (AKA, DACVP) by passing the board certifying exam.
In general terms, pathology is the study of disease and veterinary pathologists are folks who are involved in a wide range of roles with the ultimate goal of keeping animals healthy. The main areas we work in are diagnostic labs, research, and teaching.
So what DOES a pathologist do? I’m glad you asked.
To understand what happens in a diagnostic lab, it might be easiest to imagine the following scenario. Perhaps one evening you are grooming your pet when you discover a lump on the leg that you hadn’t previously noticed. You watch the lump for a few days, and it neither grows nor shrinks. Since you aren’t sure what the lump is, you take your pet to your veterinarian who also can’t tell what the lump is just by looking at it. To help decide if the lump should be surgically removed, the veterinarian gently inserts a needle into the lump and attempts to pull out some cells (some people call this a needle biopsy and others call it a fine needle aspirate, or FNA). The cells are put on a slide and evaluated microscopically so that the veterinarian can decide what course of action is appropriate for the lump, whether it’s taking a wait and see attitude or scheduling surgery to remove the mass. This approach is much kinder and gentler than just outright lopping off every little lump and bump that appears on your pet.
Looking at samples collected by needle biopsy or FNA is called cytopathology or, simply, “cytology” —“cyto-“ refers to cells, and “-ology” refers to the study of them. By looking at the cells on the slide, it’s often possible to tell whether the lump you noticed is an area of inflammation, a cyst, or some other process, including cancer. After a sample is collected, stains are applied to the slide (like dipping eggs to color them!) Surprisingly, most cells don’t have much inherent color to them, so the stain helps us find the cells. The stain also helps emphasize certain features of the cells, and these features are used to determine whether a cell is cancerous or inflammatory. Stains can also help us find infectious agents, such as bacteria or fungal organisms. Some veterinarians like to look at cytology slides microscopically before sending them out to a pathologist to evaluate, and I’m greatly in favor of this process because it can help veterinarians make certain that they are sending a representative sample to the pathologist. Note that I didn’t say “diagnostic!” There are cases where a certain lesion or lump may defy cytologic identification of the underlying process. In these instances, the veterinarian may recommend removing the mass and submitting a biopsy for histopathology.
Again, the “-pathology” part of the word indicates “the study of disease”. “Histo-“ means tissue (as compared to “cyto-“ which means cell). Understanding the difference between cytology and histology is like comparing flax seeds (cytology) versus a piece of multigrain bread that contains flax seeds (histology); as a bit of pathological humor, observe that I did not call the grains/bread analogy “cytopathology” or “histopathology” because I’m really hoping there is no pathology with your bread!
Histopathology samples are also evaluated by pathologists. With these samples, the tissue is first placed in formalin to preserve the tissue. The tissue is then embedded in a paraffin block and then sliced uber-thin (again with the bread analogy! Think of teeny, tiny little slides of bread). The slices of tissue are transferred to a slide, and stains are applied. Some of the stains are different from those used in cytopathology, but others are the same—it depends on what is being searched for with the stains. One of the benefits of histopathology lies in its ability to see how cells are relating to their neighboring cells; are they playing nicely and respecting those around them by behaving in a benign manner, or running rampant over their polite neighbors in a malignant manner). We sometimes can’t tell how cells are interacting with each other on cytopathology, because it’s just a somewhat random jumble of cells on the slide.
Whether it’s a cytopathology or histopathology sample that’s being evaluated, pathologists will write a report describing what is seen, what we think the “answer” is, and we’ll often include additional thoughts on follow up testing or an appropriate course of action, such as removal of the lesion. If you’ve ever had your dermatologist send off a skin mass or if you’re a female who has had a gynecologist collect a pap smear, you’ve employed the services of a pathologist and there is a pathology report containing information similar to what I’ve described above.
There are several other roles that pathologists play in diagnostic labs, such as looking at blood smears and urine samples as well as developing new tests and overseeing quality control/quality assurance to ensure that test results are reliable.
A lot of what we do goes on behind the scenes. It’s rare for a pet owner to communicate directly with the pathologist, partly because the pathologist may not have all information regarding your pet’s health. However, it’s pretty common for your veterinarian and the pathologist to discuss your pet’s case. In fact, there are many instances where this sort of dialogue helps fine-tune the diagnosis! As a pathologist, it’s a rare treat for me to hear a little bit about what makes your pet special when I’m chatting with your veterinarian. I also love hearing how your pet’s case turns out; I get a warm, fuzzy feeling inside when I hear that everything turned out okay. Conversely, a little part of me grieves right alongside you when I hear things didn’t turn out so well. No matter how things turn out, though, I’m grateful to have been a part of the team that helped your pet.