Cytology - General
What is cytology?
Cytology is the microscopic examination of cells that have been collected from the body. By examining the appearance of these cells, including their number, size, shape, color, internal characteristics, and how they fit together with their neighbors, it is often possible to make a diagnosis of a specific disease process.
When is cytology performed?
Cytology is most often used to diagnose the nature of "lumps and bumps" found on the surface of the body. However, cytology can also be used to evaluate:
a) internal organs such as the liver, lung, lymph node, or kidney.
b) body fluids such as urine or joint fluid.
c) abnormal fluids (called effusions) that may accumulate, especially in the chest and abdomen.
d) various surfaces of the body, both external and internal e.g. mouth, eye, breathing passages, or vagina.
What information can cytology provide?
"...cytology can tell us is whether a problem is caused by inflammation or by neoplasia."
The most important thing cytology can tell us is whether a problem is caused by inflammation or by neoplasia (literally "new growth"). If there is inflammation, cytology can often identify an underlying cause, such as bacterial infection, embedded foreign body, or allergies. If the sample appears to be neoplastic, cytology can usually determine which type of tissue is involved, and whether the neoplasm is malignant (cancer) or benign.
How does this information help the veterinarian manage a problem?
Once the veterinarian knows that a problem is inflammatory, steps can be taken to look for a specific cause (bacteria, parasite, fungus, allergies, foreign bodies etc.) in order to provide the appropriate treatment.
If cytology indicates that a growth is neoplastic, the appearance of the cells can often predict how the tumor will behave. This may determine if surgical removal is warranted, and how quickly the surgery should be scheduled.
If surgery is anticipated, prior knowledge about the type of tumor will influence the steps needed to prepare the pet for surgery (e.g. take chest x-rays to see if a malignant skin tumor has spread). The surgeon is also better able to plan how to remove a mass if the nature of the tumor is known ahead of time. Finally, by knowing beforehand what type of tumor is likely involved, the veterinarian is in a better position to predict what may happen once the tumor is removed, and may be able to answer questions such as:
Will it return?
Will it spread to other parts of the body?
Is it gone for good?
How are cells collected?
"There are several different methods for collecting cells from tissues..."
There are several different methods for collecting cells from tissues, depending on where the problem is and what type of tissue is involved. The most common technique is called fine needle aspiration, or fine needle biopsy. This simple technique to obtain a sample from the tissue in question involves using a sterile, fine gauge needle attached to an empty syringe. The needle is inserted into the middle of the tissue or pocket of fluid and the plunger of the syringe is pulled back in order to create suction and withdraw or aspirate cells from solid tissue, such as a skin lump, or to collect fluid from a site, such as a joint. (See handout Cytology - Fine needle aspiration).
Other techniques may be used to collect cells from body surfaces. A flaky, bald patch of skin might be sampled by doing a skin scraping to pull away and collect a few of the top layers of skin cells so that they can be examined. An ulcerated or oozing skin sore might be sampled by doing an impression smear, which involves pressing a clean glass slide firmly on the area to collect surface material for evaluation. Discharges from the nostril, eye, or vagina might be collected using a cotton-tipped swab, and then spread on a slide where it can be examined. A less commonly used technique is called a lavage or flush, where sterile fluid is washed over an internal surface, such as the nasal passage or trachea (breathing passage) in order to dislodge surface cells, which are then collected and examined. (See handout Cytology - Collecting Cells from Surfaces).
What are the advantages of cytology?
Cytology is a simple, quick, relatively painless and non-invasive method of gathering information about medical and surgical conditions. Minimal equipment is required, and sampling can often be performed without sedation or anesthesia. With a relatively small investment of time and materials cytology can often provide a definitive diagnosis, or can at least place the problem into a general category of illness, which often helps the veterinarian decide what further steps are needed to reach a definitive diagnosis.
What are the limitations of cytology?
"The main limitation of cytology is that the collected cells may not tell the whole story..."
The main limitation of cytology is that the collected cells may not tell the whole story about what is happening in the tissue. This may happen if samples are very small, or if the most important cells are not present in the sample. In addition, some tumors do not play by the rules - sometimes the collected cells look benign but the tumor is malignant, and in other situations, the reverse is true - the aspirated cells look malignant but the tumor is benign.
What is the next diagnostic step after cytology?
The next diagnostic step after cytology is histology. Histology is the microscopic examination of samples of whole tissue, and it is performed on a solid piece of tissue that has been collected surgically from the pet. Histology focuses on tissue architecture, and provides information about how cells are organized within a tissue, and how tissues interact with each other.
"If your pet has a growth surgically removed, always request that the tissue be sent away for histological examination."
In most cases, histology will provide a definitive diagnosis, and is generally considered the diagnostic "gold standard". Histology is often needed to determine if a tumor is benign or malignant, and is routinely recommended to confirm the cytological findings. If your pet has a growth surgically removed, always request that the tissue be sent away for histological examination.