Using cytology in exotic mammal diagnoses (Proceedings)

Aug 01, 2011

Cytology is a diagnostic tool that may be utilized on a daily basis in veterinary practice as it allows for quick answers with minimum of expense. The goal as a veterinary practitioner with a special interest in cytology is not always to make a definitive diagnosis based on cytologic results, but to help narrow the number of diagnoses on the differential list and give information on prognosis and help direct the formulation of a diagnostic and treatment plan. The presentation is designed to give a realistic view of day-to-day cytology as seen through the eyes of the practitioner at the bench microscope.

Diagnostic cytology is both a science and an art. The science is in the interpretation, requiring a familiarity with normal anatomy and histology and an understanding of pathology. The art is the collection and preparation of a diagnostic sample. That favorite utterance of the clinical pathologist must be heeded: "The results are only as good as the sample".

The cytologist must first define the cell population(s) present and then decide whether the collected specimen is primarily inflammatory, hyperplastic, a reactive lesion, neoplastic or normal. Further questions to be answered include: If inflammatory, does the specimen represent acute or chronic inflammation? Is there evidence of infectious organisms? If fluid from a body cavity is being analyzed is the effusion a transudate or an exudate? Is the mass or enlarged organ just aspirated reactive, hyperplastic or neoplastic? If neoplastic, are there criteria for malignancy? These are some of the questions the practitioner is trying to answer when interpreting cytology samples.

What makes cytology such wonderful diagnostic tool is the amount of information that can be gained in a matter of minutes. With a strong knowledge of cytology the veterinarian can obtain a quick sample that will help direct the focus of the diagnostic workup or determine overall case prognosis, many times while the client is waiting. In addition, the investment needed to add this modality to the practice setting is minimal and utilizes equipment already present in most veterinary hospitals; needles and syringes, cotton swabs, scalpel blades, glass slides, a good differential stain and microscope with oil immersion lens. The following are suggestions for improving cytological preparation and simplify interpretation in the private practice setting.

     • Have two sets of stain; dirty for obviously contaminated specimens and clean for effusions, fine needle aspirates (FNA) of masses, and other specimens without obvious contamination.
     • Utilize two microscopes at the lab work station; one for "dirty" samples such as your fecal and urine analysis, and a higher quality microscope reserved for reviewing cytology specimens.
     • Filter stain through paper towels or filter paper twice weekly to help remove bacteria and other obvious contaminants and change stain completely on a monthly basis.
     • Use a hair dryer on the low to medium heat setting for quick drying of slide specimens prior to immersion in stain fixative.
     • Oil immersion field is necessary for cytologic interpretation.
     • To aid in-hospital cytology interpretations; keep representative slides from interesting cases to review once you receive the pathologist's report.
     • Be gentle in the collection of specimens; avoid strong, intense aspiration when performing FNA's in order to prevent cell trauma and bleeding into specimen.
     • Be gentle in sample preparation; a light touch as the specimen is smeared across the glass slide.
     • Bacteria within the cell are real. Look for concurrent secondary cell degeneration. Bacteria outside the cell could be from contamination.
     • Carcinomas are of epithelial cell origin and generally exfoliate well on FNA sampling with clusters of round to oval cells visible.
     • Sarcomas are of connective tissue origin and generally do not exfoliate well on FNA sampling with few individual elongated spindle shaped cells seen.