What is cytology?
Cytology is the microscopic examination of cells 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.
When is cytology performed?
Cytology is often used to diagnose growths or masses (tumors) on the body’s surface, but it can also be used to evaluate:
- Internal organs, such as the liver, lungs, lymph nodes, and kidneys
- Body fluids, such as joint fluid
- Abnormal accumulations of fluids (called effusions), especially in the chest and abdomen
- Various surfaces of the body, both external and internal (e.g., mouth, eyes, breathing passages, skin, and vagina)
What information can cytology provide?
The most important thing cytology can tell us is whether a problem is caused by inflammation or by neoplasia (abnormal growth of tissue). If there is inflammation, cytology can often identify the underlying cause or your veterinarian can look for a specific cause (e.g., bacteria, parasite, fungus, allergies, foreign bodies) to provide the appropriate treatment.
If the sample appears to be neoplastic, cytology can usually determine which type of tissue is involved and whether the neoplasm is malignant (cancerous) or benign. This is important because further testing may be required to determine whether a malignant tumor has spread (e.g., chest X-rays or abdominal ultrasound).
Knowing the extent of a tumor’s spread is helpful for treatment planning, including whether surgical removal is required, how quickly it should be scheduled, and whether other treatment options may be helpful (e.g., chemotherapy or radiation therapy). When the nature of the tumor is known ahead of time, the surgeon can better plan how to remove the tumor and predict what may happen afterward, answering 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 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 (FNA).
FNA uses a sterile, fine-gauge needle (a needle with a very small diameter) attached to an empty syringe. The needle is inserted into the middle of the tissue and the plunger of the syringe pulled back to create suction and withdraw (aspirate) cells. Cells can be aspirated from solid tissues, such as organs or tumors, and fluid-filled tissues, such as joints or cysts.
There are several other techniques used to collect cells:
- Skin scraping: This technique collects cells from the surface of the skin (often used on flaky or ulcerated skin).
- Impression smear: A glass microscope slide is pressed firmly on an ulcerated or oozing skin sore to collect surface cells and debris for evaluation under a microscope.
- Swabs: Cotton-tipped swabs are used to collect discharge from moist skin surfaces such as the eye, nose, mouth, prepuce, or vagina.
- Lavage: This technique collects cells from internal surfaces, such as the nasal cavity, trachea (windpipe), or lungs. Sterile fluid is washed over an area to dislodge the surface cells and then suctioned back out. The recovered fluid contains a small number of cells that can be examined under the microscope.
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 samples can often be collected without sedation or anesthesia. With a relatively small investment of time and resources, cytology can often provide a definitive diagnosis. Cytology is often helpful even when it does not provide a diagnosis, because it helps to categorize the condition, which then helps determine what further steps are needed to reach a definitive diagnosis.
What are the limitations of cytology?
The main limitation of cytology is that the cells collected may not show everything that is happening in the tissue. The sample may be very small, or the most diagnostic (representative) cells may not be included in the sample. In addition, some tumor cells do not appear as expected: sometimes the cells may look benign, but the tumor is malignant, or the cells look malignant, but the tumor is benign.
What is the next step after cytology?
If cytology indicates a malignant tumor, further tests may be done to determine the extent of the tumor’s spread — a process called staging, which may include thoracic radiographs (X-rays) and abdominal ultrasound.
If cytology is not definitive, the next diagnostic step is histology. Histology is the microscopic examination of a small piece of tissue that has been collected surgically. Histology not only focuses on the individual cells, but on how they are structurally related to one another (the tissue architecture). It provides information on how the cells are organized and how related tissues (e.g., layers of skin) interact with each other, indicating any disruptions in the normal patterns.
In most cases, histology provides a definitive diagnosis and, as such, it is generally considered the best diagnostic test. It is routinely recommended to confirm cytological findings and is often required to determine whether a tumor is benign or malignant. If your pet has a growth removed surgically, always request that the tissue be sent away for histological examination.
