"I would like to send these samples out for cytology"
the veterinarian says to you. After you hear that, you may have a lot of questions. What does cytology even mean? Where is the value in this? Is this necessary? These are all great questions because collecting a sample for a cytology has a financial commitment, takes time and can dramatically change how care is administered for your pet.
Cytology is the study of cells. Cells are the individual building blocks of all tissues in the body and can also be found in body fluids like blood, urine, wound fluid or fluids that have collected in a body cavity like the chest or abdomen. Even waste like feces or ear wax can be studied with cytology to help aid in diagnosis and subsequent treatment.
In order to study these cells, a microscope must be used. A sample is taken with a needle, a swab or by directly pressing a slide onto a part of the pet's body. A benefit of cytology is that collection of these samples is typically quick and minimally or non invasive, reducing stress to the pet. After the sample has been spread onto a slide, it is stained so certain attributes of the cells stand out when analyzed under a microscope. Some stains used just apply contrast while others can highlight certain proteins or compounds hidden within cells.
One of the most common uses of cytology is to determine what a lump or bump on a pet might be made of. Though veterinarians often hear about "fatty lumps" on pets, it is actually not possible to definitively say the lump is made of fat cells unless a sample has been taken for cytology and the cells that are collected are analyzed. Look at these 2 masses:
Even though they are located in similar locations with very similar feeling and texture on physical examination, these masses are made of of very different kinds of cells. Can you tell the difference between them? Does one appear more malignant (likely to spread) or more benign just from their appearance on the outside. Though there are some very important qualities of a mass that are observed on physical exam a diagnosis and a subsequent prognosis (how the pet will do) cannot be given to the owner without a sample.
After a sample was taken from the patient on the left (or top for those on their mobile devices) and sent out to a laboratory for analysis, the mass was indeed diagnosed as a lipoma (benign fat cell tumor). After a sample was taken from the patient on the right (or below for those on their mobile devices) and sent out, this mass was diagnosed as a mast cell tumor (malignant cancer made up of a cell type called mast cells). As you can see, the cytologic examination of these two masses lead to different treatments and prognosis for each patient.
Cytology is commonly used to look at conditions on the skin, in the ears and between the toes. Similar to the example of the masses above, can you tell the difference between what is causing the inflammation in the ears below?
Both of these ears are clearly very irritated but after a sample was taken from each ear, stained and looked at under a microscope, the ear on the left (above for those on their mobile devices) was heavily infected with a yeast called Malassezia while the ear on the right (below for those on their mobile devices) was infected with a bacteria called psuedomonas which can be resistant to many first line treatments. Cytology can also be used to make sure that a treatment has been successful, ensuring that further care is not necessary.
Veterinarians are trained to identify many common cytologic findings allowing for quick diagnosis and implementation of treatment. For more challenging cytologies, especially cancer cells that are very abnormal, samples will be sent off to a pathologist who specializes in identifying these kinds of cells and has access to special stains. Your veterinarian will inform you if a sample needs to be sent to a specialist.
Finally, it is important to talk about the limitations of cytology. First, the amount of material collected is typically very small and it is possible that a sample may not fully represent the entire condition occurring. Also, when collecting the sample, the architecture of how the cells are interacting with each other can be destroyed. For certain diseases, the diagnosis can only be made using sampling techniques like biopsy that preserves architecture. If a needle is used to collect a sample, often the needle must be pushed through several layers of skin and fat before getting to the tissue intended for sampling. Cells from these other layers can contaminate the sample. Blood can also flood into the needle and contaminate the sample. Some tissues intended for sampling with a needle will not exfoliate well (tissue wont give up any cells to the needle) and therefore a non diagnostic sample is the result. Your veterinarian will explain these limitations to help prepare for the next steps if a diagnosis cannot be made from the initial cytology.
Overall, cytology in the veterinary clinic is a fast, minimally invasive method of collecting information to help provide the most specific treatment for a pet's condition.
Dr. Wes Seipel