What is cytology?
Cytology is the microscopic examination of cells that have been collected from the body. Cytology is often used to diagnose growths or masses (tumors) found on the body’s surface, but can also assess bodily fluids, internal organs (e.g., liver, lung, lymph nodes, kidney), and abnormal fluids, especially in the chest and abdomen.
There are several ways to collect the cells depending on where the problem is and what type of tissue is involved. Most commonly, fine needle aspiration (FNA) is used to collect cells. 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 or pocket of fluid and the plunger of the syringe is 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.
When is cytology used?
Cytology is often used for initial evaluation to establish a working diagnosis and plan surgery. It is a minimally invasive method of gathering preliminary information about certain medical conditions. Little equipment is required and sample collection can often be performed without sedation or anesthesia.
Cytology can also be used for on-the-spot assessment of a mass or tumor found during surgery. Cytology does not indicate a tumor’s rate of growth or whether the tumor is invading surrounding tissues, but it helps veterinarians determine what further steps are needed.
Cytology is less diagnostic than histopathology (see below) and can be misleading. Sometimes cells may look benign, but the tumor is malignant, or the cells look malignant, but the tumor is benign.
What is a biopsy?
A biopsy is the surgical removal of a tissue sample from a suspicious lesion. The biopsy is then examined under a microscope (see histopathology below). The most common biopsies are:
- Punch biopsy: A small, circular piece of tissue is removed using a biopsy punch.
- Wedge biopsy: A small slice or chunk of tissue is removed from the tumor or mass.
- Excision biopsy: The entire mass is excised (removed).
A biopsy may be taken knowing that surgical removal of the whole tumor is not possible. In other cases, a small biopsy can be useful to plan the surgical approach or determine if other treatments may be used. In many cases, it is more appropriate to remove the whole mass. Your veterinarian will give your pet a local or general anesthetic to take samples.
Is a biopsy risky for my pet?
The main risks to your pet are from their disease or from the anesthetic. In a few cases, there can be excessive bleeding, particularly when taking biopsies from tumors of the blood vessels or from organs such as the liver.
How should I take care of my pet after the biopsy?
The biopsy site must be kept clean and dry, so you should keep your pet from interfering with it. Report any loss of stitches or significant swelling or bleeding to your veterinarian. If you require additional advice on postsurgical care, ask your veterinary healthcare team. A surgical “onesie” or an Elizabethan collar (e-collar or cone) may be recommended to prevent your pet from licking the incision.
What happens to the tissue sample?
After the biopsy, your veterinarian will place the tissue sample into a preservative solution and submit it to a diagnostic laboratory. In the laboratory, the process of histopathology begins. Results often take up to a week to be returned.
What is a veterinary pathologist?
A veterinary pathologist is a licensed veterinarian with specialized training who can identify abnormalities in samples from your pet that help diagnose disease (e.g., tissues, blood or urine). Your veterinarian can work with them to diagnose disease in your pet and develop the best treatment plan.
What is histopathology?
Histopathology is the examination of whole tissue samples. It is performed on a solid piece of tissue that has been collected surgically. The piece of tissue is prepared through a process called histology by preserving, thinly slicing, or sectioning the tissue sample, and then staining it with dyes. Once prepared, the tissue sections are examined under the microscope by a veterinary pathologist. Histopathology focuses on the architecture of the tissue and provides more information about the tissue than cytology.
What can histopathology tell me about my pet’s tumor?
A pet’s lumps and bumps are often impossible to diagnose by simply looking at them, but a pathologist examining cells under the microscope (histopathology) can usually assign a classification to a tumor and make a diagnosis. Cancers (malignant tumors) are usually classified by their tissue of origin and appearance. If the entire tumor is submitted for examination, the pathologist may also offer an opinion about whether the tumor has been completely removed.
As well as a diagnosis, the veterinary pathologist usually provides a prognosis (an opinion on the likely course of the disease). It will describe the probability of local recurrence or metastasis (spread of the cancer cells to other parts of the body). In many cases, diagnosis with prognosis can indicate whether a cure is possible. Unfortunately, surgical removal and other treatments may only give temporary remission before recurrence or spread.
A lot of information has been accumulated through the years on different types of tumors and that previous experience helps determine factors such as survival time. Pathology results help you and your veterinarian to plan future care for your pet.
Are there any limitations to these techniques?
The behavior of some tumors is difficult to predict. Even when a positive prognosis is made, tumors sometimes recur or metastasize (spread to other areas). Prognoses (the likely outcomes) are based on probabilities, and nothing is 100% guaranteed. Occasionally, a diagnosis may not be possible, particularly when it is difficult to obtain a large enough sample. Results are sometimes inconclusive, and a second biopsy is needed.
