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.
When is cytology performed?
Cytology is most often used to diagnose the nature of "lumps and bumps" found in the skin and in the layer just under the skin. However, cytology is also used to evaluate body organs such as the liver, lymph node, lung, or kidney, and is used to assess body fluids. These fluids may be normal body fluids such as urine or joint fluid, but may come from a fluid-filled growth, or an abnormal accumulation of fluid (called an effusion) that sometimes develops in the chest and/or abdomen.
How are cells collected?
The most common technique for collecting cells is called fine needle aspiration (FNA), or fine needle biopsy. This technique is used to collect cells from solid tissue, and to harvest free fluid from sites where it has accumulated. The FNA technique is very simple: a sterile fine gauge needle is attached to an empty syringe, the needle is introduced into the target tissue or pocket of fluid, and the plunger of the syringe is pulled back to create suction, which pulls cells or fluid from the site.
Is any special preparation required before collecting the sample?
For routine sampling of lumps and bumps on the body surface, special preparation of the skin is not usually required, although a simple disinfectant like alcohol may be applied prior to sample collection.
However, if the veterinarian plans to submit the sample to see if bacteria are present, or wants to sample an internal organ, such as the liver, then full surgical preparation of the skin is required. This involves shaving the fur, cleaning and disinfecting the skin, and draping the site as for surgery. The veterinarian would then employ sterile technique during collection and handling of the sample.
Cytology specimens may also be collected during an ultrasound examination. These samples are called "ultrasound guided" since identification of the tissue site and positioning of the sampling needle are done with help of the ultrasound image.
What happens to the collected cells?
When solid tissue is aspirated, a small amount of material accumulates in the needle and hub of the syringe. This material is immediately and gently expelled onto a clean glass slide, thinly spread, and rapidly dried by waving the slide in the air, or by placing it in front of a fan or portable hair dryer. This is called making an "air-dried smear" The slide is then stained with special dyes and examined under the microscope.
When fluids are sampled, air dried smears are also made. However, since fluid samples are generally more voluminous that aspirates from solid tissue, there may be extra fluid left over after the air-dried slides are made. This fluid can be run through a counting analyzer at the laboratory, and both the number of cells and the amount of protein in the fluid can be measured. This information may help with the diagnosis.
Is FNA always diagnostic?
Fine needle aspiration is not always diagnostic, but in most cases, the technique will 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 is the next diagnostic step after cytology?
The next diagnostic step after cytology is histology. Histology is the microscopic examination of whole tissue, and it is performed on a solid piece of tissue that has been collected surgically from the dog. Histology focuses on tissue architecture, and provides information about how cells are organized within a tissue, and how tissues interact with each other
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 dog has a growth surgically removed, always request that the tissue be sent away for histological examination. ?
Based on material written by Kristiina Ruotsalo, DVM, DVSc, Dip ACVP &
Margo S. Tant BSc, DVM, DVSc. and modified with permission from Lifelearn Inc.
© Copyright 2004 Lifelearn Inc.
