Intraoral cytology - DVM
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Intraoral cytology
Ensure you know the fundamentals


Examining the sample

Evaluating stained cells from oral masses is not difficult. A high-quality microscope is essential. The 40X objective can be replaced with 50X oil immersion objective for improved cytologic evaluation. First scan the slide under low magnification to identify areas of increased cellularity. Once an interesting area has been identified, use 50X (oil) and 100X (oil) for closer examination.

Examination of the cells should yield a diagnosis of an inflammation, neoplasia or a mixed-cell population (both inflammatory and neoplastic). Good biopsy technique, smear fixation and staining technique are essential, as is proper use of a high-quality microscope. A negative (e.g., tumor-negative) report is less reliable than a positive report. This is an important concept to embrace. The result is only as good as where the sample was taken from.

Photo 3: Cytologic examination of a sample of the lesion in Photo 1 reveals a mixed inflammatory reaction.
If the reaction is inflammatory, try to further classify it as to type (neutrophilic, eosinophilic, lymphocytic or macrophagic) and to identify etiologic agents (Photo 3). Neutrophils may appear with degenerative changes affecting the nucleus, occurring once the neutrophil has left the circulation to fight an infection; the resulting appearance is nuclear swelling. Toxic changes to the neutrophil affect the cytoplasm and manifest as Döhle bodies, cytoplasmic basophilia and foaminess. These changes occur during formation of the neutrophil in the marrow and suggest altered development that can be associated with sepsis. If you see toxic change in neutrophils in inflammatory lesions, expect to also see it on neutrophils in a complete blood count since it developed in the marrow.

Photo 4: A mixed-cell population in a case of feline oral squamous cell carcinoma.
Unlike inflammation, neoplastic samples generally contain homogeneous populations of a single cell type. Although mixed-cell populations are sometimes seen, these usually involve a neoplastic area with concurrent inflammation (Photo 4).

Neoplasia must be differentiated as either benign or malignant. Benign neoplasia is represented by proliferating cells that often resemble the tissue from which they arose and lack criteria of malignancy (Photos 5A and 5B). The cells are of the same type and are relatively uniform in appearance. Cells that demonstrate at least three criteria of malignancy help to determine a cytologic diagnosis of malignancy (Photos 6A and 6B).

Photo 5A: Inflamed enlargement on the attached gingiva in a 4-year-old dog.

Photo 5B: Cytologic examination of a sample reveals reactive fibroplasia.

Photo 6A: A mobile maxillary first molar in an 11-year-old German Shepherd.

Photo 6B: Cytologic examination of a sample reveals sheets of cohesive cells with malignant criteria (anisokaryosis, pleomorphism, high nuclear/cytoplasm ratio, coarse nuclear chromatin) indicative of squamous cell carcinoma.

Criteria of malignancy can include any of the following:

  • Anisokaryosis—unusual variation in overall nuclear size (Photo 7).
  • Pleomorphism—variability in the size and shape of the same cell type (Photo 8).
  • High or variable nuclear/cytoplasm ratio—specifically an increased ratio of nucleus to cytoplasm (Photo 9).
  • Increased mitotic activity—mitosis is rare in normal tissue, and cells usually divide evenly in two; any increase in the presence of mitotic figures or cells that are not dividing equally would be considered malignant criteria.
  • Coarse chromatin pattern—coarser than normal and may appear ropelike or cordlike.
  • Nuclear molding—a deformation of nuclei by other nuclei within the same cell or adjacent cells.
  • Multinucleation—multiple nuclei within a cell.
  • Nucleoli that vary in size, shape and numbers—anisonucleoliosis, angular nucleoli or multiple nucleoli.

Photo 7: Anisokaryosis.

Photo 8: Pleomorphism.

Photo 9: Increased nuclear/cytoplasm ratio.

Samples that have been classified as malignant should be further evaluated to determine the cell type involved. The basic tumor categories seen in mammals include epithelial, mesenchymal, round cell and neuroendocrine.

Epithelial cell tumors are carcinomas. The samples tend to be highly cellular and often exfoliate in clumps or sheets. Mesenchymal cell tumors are sarcomas and are usually less cellular. The cells tend to exfoliate singly or in wispy spindles. Round cell tumors exfoliate but usually are not in clumps or clusters. Oral round cell tumors include lymphoma, mast cell, plasma cell and melanoma. Cytology samples should be sent to a board-certified pathologist for confirmation.


Source: DVM360 MAGAZINE,
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