This is a gowth called a Histiocytoma. These are usually found in young dogs on the limbs, face and ears and the vast marity spontaneously regress within a few weeks/months. This particular one was found in a 12 year old Border Collie. Diagnosis was made by cytological examinantion of fine needle aspirate. Mast Cell tumous can also look like these and was the major differential in this dog.
Cytology of fine needle aspirate taken from the above growth. The large purple cells are histiocytoma cells.
Another histiocytoma above the eye on a young Chow Dog
Cytology is one extremely useful diagnostic tool that is used on a daily basis in veterinary dermatology.
Examples of situations where cytology is useful are:-
Examination of discharges from the ear. This allows identification of organisms such as bacteria and yeasts, inflammatory cells and also in what numbers. If rod shaped bacteria are seen on cytology (which could indicate pseudomonas) this is followed up by swabs being taken for bacteriology and antibiotic sensitivity testing.
Examination of surface skin cytology using sellotape impressions . This is used primarily for the identification of yeasts (Malassezia) often present in abnormal numbers in allergic skin disease and in oily seborrhoea.
Examination of pustule contents. Not all pustules are caused by infection. Autoimmune diseases such as pemphigus foliaceus can present as a pustular disorder. Cytology of a pustule can reveal bacteria and white blood cells in a case of pyoderma, whereas a pustule in pemphigus will only show white blood cells (no bacteria) and cells called acanthocytes.
Fine needle aspirate (FNA). This is a method where cells are taken from masses such as tumours or those caused by infection with bacteria or fungal organisms. A sterile hypodermic needle is placed in the mass and cells from the mass are drawn into the needle by applying a vaccum with a 10ml syringe. The contents of the needle are then sprayed onto a microscope slide, stained and examined under the microscope. One very common reason for using this technique is with skin tumours as one particular tumour, the Mast Cell Tumour (MCT), can look like many other different types of skin tumour and the characteristic mast cells are very easily seen on an FNA. As MCTs can be potentially very serious, it is important to have made a diagnosis before excision is carried out with the correct margins.
Impression Smear. This simple procedure involves pressing a slide against an ulcerated skin lesion to pick up some of the cells on the surface that may help in making a diagnosis. One typical example is the finding of inflammatory cells called eosinophils in cats with lesions associated with the eosinophilic granuloma complex (EGC) such as a rodent ulcer on the lip.
Cytological samples are stained with special chemical stains to allow visualisation of the cellular and other material. This is done in our own laboratory and I read the cytology specimens myself, so we can have an answer within minutes.
The first stage in examining a smear. Staining in Rapi-Diff to allow visualisation of cells, micro-organisms. This is the first stage of the 3-stage process and is the fixing of the preparation in alcohol so that the smear does not come off the slide and cellular detail is preserved.
Examining a smear under the microscope. Most of our cytology is done in-house. Occasionally, if we are unsure, samples are sent away to a professional lab.
