Pearls
- In cytology, the sample is everything: garbage in = garbage out.
- Cytology is quick, requires no sedation, and is relatively noninvasive and inexpensive. Often a definitive diagnosis can be made based on cytology alone.
- When sampling solid masses by fine needle, use a 22 or 25 gauge needle. Large animals do not require large needles! Needles larger than 22 gauge usually result in considerable blood contamination of the sample which greatly impairs the diagnostic value of the submission.
- If a fluid sample is obtained, deposit it into an EDTA tube. Even samples that do not appear bloody may clot if anticoagulant is not used. Submit the EDTA sample together with air dried, unstained smears. A line preparation is useful for cell poor fluids (watery, non-cloudy fluids).
- Submit several air dried, unstained smears. Do not expose the slides to humidity (do not refrigerate) or formalin fumes (do not pack together with tissues for histopathology).
- When examining a cytologic preparation, spend time on low magnification assessing the cellularity, background, and any large structures which may not be as obvious on higher magnification. Try to decide if the lesion is inflammatory or noninflammatory (though these are not necessarily mutually exclusive). If inflammatory, identify the cell types and look for a potential etiology (bacteria, yeast, parasites, etc.). If noninflammatory, do the cells look neoplastic? If neoplastic, are the cells epithelial or mesenchymal? Mesenchymal tumors are subdivided into spindle cell and discrete round cell.
- Look for criteria of malignancy to determine if the tumor is malignant or benign. Keep in mind that these criteria apply primarily to carcinomas and spindle cell sarcomas, but less so to round cell tumors.
- To diagnose lymphosarcoma, look for a homogeneous (uniform) population of medium to large lymphocytes. A heterogeneous population with small lymphocytes predominating is expected in normal or reactive lymph nodes.
- Fluid samples are categorized, based on nucleated cell count and protein concentration, as transudates, modified transudates, or exudates. The differential diagnoses are more focused, based on these categories.
- Very bloody effusions (with cell counts and protein concentration approximating peripheral blood) suggest internal hemorrhage. It is important to try to determine if iatrogenic blood contamination occurred (as a result of the procedure), or if the sample is representative of the lesion. If there has been prior hemorrhage, there should be evidence of erythrophagia by macrophages. Hemosiderin granules can also be seen in macrophages as evidence of previous hemorrhage. Also, platelets will disappear quickly following a single episode of hemorrhage.
- Chylous effusions commonly indicate lymphatic hypertension, which could be due to cardiac disease, neoplasia, inflammatory disease, heartworm infestation, or other cause. In some circumstances, the cause remains unknown (idiopathic) despite thorough investigation.
