Ear Cytology For Dogs And Cats

Cytology is a technique used in many aspects of veterinary and human medical practice.

“Cyto” comes from the Greek kytos, meaning “cell.” Logos is Greek for “science.” So, cytology is the science (or study) of cells. More specifically in everyday use cytology is used to study cells placed on a microscope slide from a body source.

Today we are only concerned with cytology of canine and feline ears.

Most commonly ear cytology in veterinary practice is used to determine the cause of inflammatory processes, usually infection and/or allergy-related. Cytology can also help us find cancerous cells growing in the ear canal(s).

Cytology starts with taking a specimen from the ear, obtained with a cotton swab. Separate swabs are used for opposite ears, as the same process is not always active in both ears at the same time. Gentleness is indicated in obtaining the offending material, not only to prevent exacerbating pain for the patient, but to prevent artifacts, as well. Rough handling of delicate blood and skin cells might prevent us from identifying important factors in a dog or cat’s ear problem.

Convention guides us to place the specimen from the left ear on the left side of a frosted-end microscope slide, the right ear’s sample on the right (see photo).

The frosted end allows patient identification as well as the "up" side of a microscope slide.

The frosted end allows patient identification as well as the "up" side of a microscope slide.

Again, a gentle technique is important, so the swab rolls the material onto the slide instead of dragging it.

Just as “Coke” is a generic term for soft drinks and “Kleenex” has become a standardized term for tissues, Diff Quik is a term clinicians use to describe any brand of a combination of three staining materials that are variants of the Romanovsky type. Simply looking at the microscope slide unstained, even at high magnification, would not tell us much because individual structures’ characteristics couldn’t be identified.

Diff Quik stains consist of a fixative (for stabilizing cell structures), an eosinophilic (red) stain and a basophilic (blue) stain.

Many, many other types of stains may be used to evaluate various kinds of cytologies. Diff Quik is simply the most common in clinical use.

If the material from an ear is particularly moist, the slide might be air-dried, hair-dryer dried or placed atop a source of gentle heat. One colleague uses a coffee-mug warmer.

The slide is then immersed into each color in the order listed above. Standard timing is ten seconds or “dips” in each color, but specimens suspected to be difficult to “fix” may be left in station one longer. If a doctor or technician is especially interested in the eosinophilic- or basophilic-staining structures he will leave the slide in the appropriate station longer.

Excess stain is then rinsed from the slide with tap water and the slide is dried by the method preferred by the operator.

Next comes evaluation under the microscope. To facilitate easy focusing the microscopist starts with a very low power objective called scanning. When the field is clear he switches to “high-dry,” which has the next step in higher magnification. He may use either or both of these to choose the field he wants to evaluate more closely, based on the patient’s and/or infective cells he sees. Finally the highest magnification is used, oil immersion.

Oil immersion is so-named because a special synthetic oil is introduced between the microscope objective and the stained slide. The oil displaces the tiny bit of air between the two that would otherwise distort the operator’s view.

Common infectious organisms in pets’ ears include bacteria and yeast. Bacteria may be of a round shape, cocci, or a rod shape bacilli. Yeast are usually of the genus Malasezzia, with the most common organism being Malasezzia pachydermatis.

Now, when your pet’s doctor performs cytology on your pet’s ears, you will know that a lot of technique and training go into both the preparation and the evaluation of the slide.
LSTAIN

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