Cat & Dog - Cytology Techniques

What is cytology?

Cytology is the microscopic examination of cells collected from the body.  The appearance of these cells including their numbers, size, shape, colour and internal characteristics can often lead to the diagnosis of a problem.

When is cytology performed?

Cytology is a frequently used diagnostic tool when investigating abnormal masses - (lumps and bumps).  It is also used to investigate problems associated with:

• body organs such as the liver, lungs, lymph nodes or kidneys
• fluids such as urine or joint fluid
• effusions (abnormal fluid accumulations) especially in the chest and abdomen
• both internal and external body surfaces (mouth, eye, nose, bladder and bowel, etc.)

What information can cytology provide?

Cytology often answers the question - is this problem neoplastic (cancerous) or is it due to inflammation?

If the sample appears neoplastic, cytological examination can usually determine which type of tissue is involved and whether the neoplasm (mass) is malignant (cancerous) or benign.

If there is inflammation the underlying cause can often be determined.  For example, the causes can be a foreign body or an allergic reaction, etc.

This information is important when establishing a diagnosis.  For example, if the problem is inflammatory the next step will be to establish the cause (e.g. bacteria, parasites, fungi, allergies, etc.).  If cytology indicates a malignant neoplasm, treatment strategies can be planned and discussed and a more accurate prognosis regarding treatment can be offered.

How are the cell samples obtained?

This depends on the problem and the site.  Collecting cells from body surfaces may involve scrapings, impression smears, swabs or flushing (lavage) techniques.

Skin scraping

This is a simple, relatively painless technique used to obtain a sample when there is a patch of flaky skin, a bald spot, or mildly ulcerated skin lump.  It involves gently scraping the lesion with a sterile scalpel blade and then transferring the material on to a microscope slide which can then be processed by the laboratory.

Impression smears

This technique is used with wounds or large ulcerating/oozing sores on the skin.  A microscope slide is gently pressed against the affected area and then lifted off.  This is repeated several times and each time a small amount of material sticks to the slide and is then dried.  It is then processed in the laboratory.

Both scrapings and impression smears are useful for detecting skin parasites, bacteria, yeasts, fungi, inflammatory cells and any abnormal tissue cells.

Swabs

A sterile bacterial swab is used to collect samples of discharge (e.g. from a burst abscess) or to harvest cells from moist surfaces (e.g. mouth, eye, nostril or vagina, etc).  For cytology examination the swab is then rolled across a clean microscope slide which is dried, processed and then examined to reveal any inflammatory cells, infectious organisms (e.g. bacteria, yeasts, fungi, etc.) or abnormal cells.  Further bacteriological swabs may be taken and put into transport media to be sent to an appropriate laboratory for further tests.

Flushing (lavage)

This is a specialised technique used to collect cells from surfaces within the body such as the nasal cavity, trachea (windpipe) or lungs.  A syringe filled with sterile saline (salt water) or similar fluid is attached to a flexible catheter (very small tube).  This is passed into the area under investigation.  A small amount of the fluid is flushed into the area and then suctioned back without delay.  The recovered fluid usually contains cells that can be examined under the microscope.  The technique is known as flushing, lavage or washing and is often helpful in identifying inflammation, infection and possible tumours.

Fine needle biopsy, or fine needle aspiration (FNA)

This technique involves inserting a very fine gauge needle attached to an empty sterile syringe into the target tissue or pocket of fluid. The syringe is then used to suck up some of the fluid or cells.  If the site is deep within the body (e.g. liver, gall bladder, etc.) ultrasound guided techniques may be used.  The ultrasound is used to identify the exact site and to help with the placement of the needle.  Once collected the sample is placed on a clean microscope slide, dried and stained.

Such techniques are used to examine cells from organs (e.g. liver, lymph nodes, lungs, kidneys etc.) and also to assess body fluids (e.g. urine, joint fluid or abnormal fluids such as from a fluid filled cyst).

Are cytology techniques diagnostic?

In the majority of cases cytology samples provide reasonably definitive diagnoses.  In some cases histology may be necessary.  This is the microscopic examination of tissue and it is used if diagnosis is still in doubt.

Histology is frequently needed to determine if a tumour is benign or malignant.