What is cytology?
Cytology is the microscopic examination of cells that have been collected from the body. It is often possible to diagnose a disease by examining the appearance of these cells, including their number, size, shape, color, internal characteristics, and how they fit together with their neighbors.
How are cells collected from body surfaces?
There are different methods for collecting cells from body surfaces, and each is used in slightly different circumstances.
Skin Scraping: This technique is used to scrape cells off the skin’s surface, for example, on a patch of flaky skin, a bald spot, or an ulcerated bump. With this technique, a sterile scalpel blade is held at right angles to the skin and firmly dragged across the skin surface several times, scraping away the top layers of skin cells.
The material that accumulates on the scalpel blade is spread thinly on a glass slide. The slide is then stained with special dyes and examined under the microscope. This technique is good for detecting the presence of skin parasites, bacteria, yeasts, fungi, inflammatory cells, or abnormal skin cells. The skin may bleed a little after being scraped, but the wound is minor (no more than a scratch) and usually does not cause any discomfort.
Impression Smears: When there is a draining wound or an oozing sore, impression smears are used to examine the surface material. Impression smears are made by pressing a clean glass slide firmly against the affected area and then lifting it away. This action is repeated several times, and each time a small amount of material sticks to the slide.
If there is crusting or built-up surface debris, impression smears are often made twice: once before and once after cleaning the area to remove the crust and debris. Impression smears, like skin scrapings, are good for detecting the presence of inflammation, infectious organisms, and abnormal tissue cells.
Swabs: A swab (usually cotton-tipped) is used to collect discharge from moist surfaces like the mouth, eye, ear, nostril, vagina, and around the penis. The swab is wiped firmly across the affected area and then rolled against a glass slide, so the cells stick to the slide. The resulting smear often reveals inflammatory cells, infectious organisms, and small numbers of tissue cells from the surface that can be examined for signs of abnormality.
Flushes: This technique is used to collect cells from surfaces within the body, such as the nasal cavity, trachea (windpipe), lungs, or prostate gland. The pet is usually placed under sedation or anesthesia, and a thin, flexible, and sterile catheter is passed into the area being investigated. A small amount of sterile fluid is flushed forcefully into the area and then quickly suctioned back out. The recovered fluid contains a small number of cells that can be examined. A flush or lavage is often helpful to identify inflammation, infection, and cancer.
Do cytology samples from surfaces always give a clear answer?
Examination of surface cells is often helpful, and in some circumstances can provide a definitive diagnosis. However, in many cases, surface cells do not show everything that is happening. Additional samples are often needed from tissues below the surface, which are obtained through a technique called fine needle aspiration (FNA). FNA uses a fine-gauge needle (a needle with a very small diameter) attached to a syringe to aspirate (remove) cells from below the surface.
