Cytology, Biopsy, and Histopathology
What is cytology?
Cytology is the microscopic examination of cell samples. These samples can be collected from any area of the body. Cytology is often used to diagnose growths or masses (tumors) found on the surface of the body, but can also be used to assess bodily fluids, internal organs (e.g., liver, lung, lymph nodes, kidney), and abnormal fluids that may accumulate, 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 or fine needle biopsy is performed to collect cells. This technique 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 or aspirate cells from solid tissue, such as a skin lump, or to collect fluid from a site, such as a joint (see handout “Fine Needle Aspiration”).
Other techniques may be used, such as:
- Skin scraping. This technique pulls a few cells away from the surface of the skin (often used on flaky, or ulcerated skin).
- Impression smear. In this technique, a glass microscope slide is pressed firmly on an ulcerated lesion. This allows the surface materials to be collected and examined under a microscope.
- Cotton-tipped swabs. Cotton-tipped swabs are used to collect discharge and cells from moist skin surfaces such as the eye, nose, mouth, or vagina.
- Lavage. This technique is used to collect cells from internal surfaces such as the nasal cavity, trachea (windpipe), or lung. Fluid is flushed into the area and then suctioned back out. Cells are collected in the fluid and are examined under the microscope.
These techniques are described in more detail in the handout “Cytology – Surface Cell Samples”.
When is cytology used?
Cytology is often used for preliminary evaluation to establish a working diagnosis and as needed, plan surgery. It is a non-invasive method for gathering preliminary information about certain medical conditions. Little equipment is required and sample collection can often be performed without sedation or anesthesia. The technique can also be used at the time of surgery for on-the-spot assessment of a mass or tumor that has been found. Cytology does not indicate the rate of growth of a tumor or whether the tumor may be invading surrounding tissues, but it often helps veterinarians determine what further steps are needed.
Cytology is less diagnostic than histopathology (see below) and can be misleading for some tumors – sometimes cells that look benign are indeed malignant and sometimes the opposite is true.
What is a biopsy?
A biopsy is the surgical removal of a representative sample of tissue from a suspicious lesion. The biopsy is then processed and is 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, or
- excision biopsy - the entire mass is excised or removed.
In some cases, a biopsy it 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, thereby increasing the chances of a successful outcome. However, in many cases, particularly when it is easy to get good surgical margins (area of ‘healthy’ tissue) around the mass, it is more appropriate to remove the whole mass. Your veterinarian will give your pet a local or general anesthetic in order to take samples.
Is a biopsy risky for my pet?
The main risks to your pet are either from the disease your pet has or from the anesthetic. In a few cases, particularly when taking biopsies from tumors of the blood vessels, or from organs such as the liver, there can be excessive bleeding.
How can I nurse my pet after the biopsy?
After the biopsy, your pet should not be allowed to interfere with the biopsy site, which needs to be kept clean and dry. Report any loss of stitches or significant swelling or bleeding to your veterinarian. If you require additional advice on post-surgical care, please ask your veterinary healthcare team. An Elizabethan collar (e-collar or cone) may be recommended to prevent your pet from being able to lick at the incision.
What happens to the biopsy?
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.
What is histopathology?
Histopathology is the examination of samples of whole tissues and 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, and staining the tissue sample 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.
With this type of laboratory examination, the accuracy of a diagnosis is usually high. The veterinary pathologist can often offer an opinion on the likely course of the disease, what is called the prognosis. If the entire mass of tissue (the whole tumor) is submitted for examination, the pathologist may also offer an opinion as to whether the tumor has been completely removed i.e., if there are wide-margins (the amount of ‘healthy’ tissue surrounding the tumor). This information helps your veterinarian to decide the best course of treatment for your pet.
Who is the veterinary pathologist?
As with human medicine, the knowledge and skills of veterinary professionals are ever-expanding with increasing need for specialization and specialists in different subjects. The veterinary pathologist is a registered veterinarian who gives an expert opinion, based on specialized training and experience. Your veterinarian will base the treatment plan on the pathology report.
What can histopathology tell me about the tumor my pet has?
It is often impossible to say what ‘lumps and bumps are just by looking at them, but with histopathology (examining cells under the microscope) the pathologist can usually assign a classification and make a diagnosis.
Cancers (malignant tumors) are usually classified by their tissue of origin and appearance.
How will I know how the cancer will behave?
As well as a diagnosis, the veterinary pathologist usually provides a prognosis, which describes the probability of local recurrence or metastasis (spread of the cancer cells to other parts of the body).
In many cases, the diagnosis with prognosis can indicate whether a cure is possible. Unfortunately, there are some cases where surgical removal and/or other treatments will only give temporary remission before recurrence or spread. The pathology results will 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, sometimes tumors will recur or metastasize (spread to other areas). Prognoses (the likely outcomes) are based on probabilities, and nothing is 100% guaranteed.
Occasionally, particularly when it is difficult to obtain a large enough sample, a diagnosis may not be possible.
Sometimes results are inconclusive, and a second biopsy is needed.
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