Page 30 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Guidelines to Cytology Smear Examination
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3.1 Step-by-step Approach to the Slide Examination
VetBooks.ir and Description

Step 1: Low-power magnification (4×, 10×, 20×)
Smears should initially be scanned with low-power objectives to gain an appreciation of the
overall cellularity and cell preservation. It is important to examine the entire smear, including
the feathered edges.
The following points should be considered when examining a cytology smear at low
magnification:

• Is the cellularity adequate for the type of specimen and collection technique? Is it enough
to attempt a diagnosis?
• Are the cells adequately stained and well preserved?
• Is there any non-cellular background material that may be of significance, such as matrix,
cytoplasmic fragments (lymphoglandular bodies), etc?
• Is there a monomorphic or a mixed population of nucleated cells? Are these homogenously
distributed throughout the smear?
• Is there evidence of any typical cell arrangement and/or cytoarchitecture?
• What types of cells are present (e.g. inflammatory cells, tissue cells, or a mixture of the two)?

Step 2: High-power magnification (40×, 50×, 100×)
High magnification allows for a more detailed evaluation of the cell morphology details.
• Inflammatory cells
The inflammatory process should be classified based on the predominant cell type/types. The
morphology of the inflammatory cells should be carefully examined for the presence of signifi-
cant changes, such as degenerative changes in the neutrophils or phagocytic activity by the
macrophages, etc.
• Infectious agents
When appropriate, a thorough examination of the slides for the presence of infectious
agents (bacteria, fungi, protozoa, etc.) should be made. Bacteria are usually found in the
background of the smears and/or phagocytosed by the neutrophils. Fungi and yeasts are
usually found in the background, surrounded by the inflammatory cells, or within macro-
phages. When a fungal infection is suspected and the aspirates are highly cellular, hyphae
are usually hidden amongst the inflammatory cells in the thickest areas of the smear. Proto-
zoa are generally found within macrophages.
• Tissue cells
These can be classified into epithelial, mesenchymal or round cells based on their arrange-
ment and morphology.
When writing a cytology report, the shape and arrangement of the cells, morphology of
the nucleus and cytoplasmic features should be described.
• Cell type morphology and arrangement:
• Epithelial cells
• Shape: cuboidal, polygonal or columnar.
• Arrangement: cells often exfoliate in cohesive clusters. Their architecture varies
depending on the tissue of origin, as illustrated in fig. 3.1.