| Full sample interpretation may require a professional laboratory, but much information can be obtained in the practice. It is axiomatic that full interpretation requires a good- quality sample. Many samples taken in practice environments are unsuitable for full interpretation. Techniques that appear to be simple may require considerable practice to yield consistent quality. A high quality microscope with a range of objective lenses, including oil immersion, is required to examine smears. |
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Inflammation: |
| Clinicians must be able to recognize the basic inflammatory cells—neutrophils, eosinophils, lymphocytes, macrophages, and plasma cells. Some tumors contain a large number of inflammatory cells, but these are very uncommon. If inflammatory cells are exclusively present in a sample, it is almost certainly a primary inflammatory lesion. |
| A large number of
neutrophils in a cytology preparation indicates acute inflammation and is usually accompanied by smaller numbers of lymphocytes and macrophages. This is most often caused by an infection or foreign body reaction, including furunculotic reactions directed against hair and keratin embedded in the soft tissue. The cytoplasm of neutrophils may contain causative organisms. |
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Macrophages are medium-sized round cells with oval, sometimes indented, nuclei and moderate amounts of usually vacuolated, foamy cytoplasm. These cells phagocytize organisms, other cells, and debris. They are associated with any tissue damage but especially with chronic inflammation. Chronic inflammation leads to a very mixed cell population, including neutrophils, but there is a much higher proportion of macrophages, plasma cells, and lymphocytes. Spindle-shaped
fibroblasts are often also present. Macrophages are also seen within the contents of cysts. |
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Eosinophils can often be seen in association with mast cells. They are associated with allergies and also are prominent in parasitic diseases, superficial cutaneous viral infection in cats, and fungal infections. They are the predominant cell type in specific eosinophilic conditions, eg, eosinophilic granuloma in cats (rarely dogs) and eosinophilic collagenolytic granuloma in horses. Some canine cutaneous mast cell tumors have a very high proportion of eosinophils
and very few mast cells. Eosinophils can be a less specific part of the inflammatory response in certain species (eg, rabbits). Heterophils in birds and reptiles are similar morphologically to eosinophils. |
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Lymphocytes are part of the chronic inflammatory response and are not specific for a particular stimulus. Most are small, with nuclei approximately the same size as RBC. If mostly medium to large lymphocytes are present, lymphoma should be considered. |
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Histiocytes are part of the macrophage cell family but appear less activated than macrophages and have many fewer cytoplasmic vacuoles. They are found in cutaneous histiocytoses in dogs and granulomas in all species. |
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Multinucleated cells are usually seen in small numbers along with other inflammatory cells as part of a granulomatous reaction. They are particularly common in fungal infections and reaction to foreign material, although this association is much less specific in birds and reptiles. |
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Fibroblasts proliferate as part of the repair reaction associated with tissue damage. When fibroblasts are aspirated from tissue, the cells usually lose their spindle shape and become round, but a few will retain their elongated shape. They have round or oval nuclei, indistinct nucleoli, and moderate amounts of uniform, pale blue-staining cytoplasm. The cytoplasmic boundaries are indistinct with a “wispy” appearance. Fibroblasts may look the same as low-grade spindle
cell tumors, and these cannot be definitively distinguished cytologically. If found with inflammatory cells, the spindle cells are most often reactive, but neoplasia cannot be ruled out. |
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Neoplasia: |
| Ideally, the first stage in the cytologic interpretation of neoplasia is determination of the cells’ tissue type. Occasionally, however, this is not possible. The next stage would then be determination of the likely behavior of the cells, which can be done without specifically identifying the cell type. There are 3 basic cell types: epithelial, mesenchymal (ie, supporting or connective), and round.
Epithelial cells are round, cuboidal, or polygonal and tend to adhere tightly to each other and exfoliate in clusters or sheets. They have a sharp cytoplasmic outline and exfoliate in moderate numbers.
Mesenchymal cells are tightly adherent and usually exfoliate in very low numbers as single cells or very small, loose aggregates. They are classically spindle shaped but usually become round and plump when removed from the body.
Round cells have little or no adherence in the body and therefore usually exfoliate in large numbers and lie individually in the smear with no clumping. Cells of this category include mast cells, lymphocytes, histiocytes, plasma cells, and cells of transmissible venereal tumors. |
| Classification of the cell type and likely behavior may require tissue biopsy; with very few exceptions, histology will be necessary for a definitive diagnosis. However, it may be possible to obtain further information from a cytology sample. |
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