Cytological Examination of Secretions From the Paranasal Sinuses in Horses.

The objective of this study was to determine whether the assessment of cytological features of secretions from the paranasal sinuses represents a useful diagnostic tool in equine sinusitis to distinguish between different etiologies. Secretion samples from 50 horses with sinusitis and 10 healthy horses were taken transendoscopically from the drainage angle of the nasomaxillary aperture using a Swing Tip catheter. An additional direct sample from the caudal maxillary sinus was taken from all healthy horses after trephination. A direct sample was obtained from the affected sinus in 19 diseased horses after osteotomy. Samples were smeared on microscope slides and dyed using "Pappenheim stain" for cytological evaluation. Smears from horses with sinusitis (primary n = 14, dental n = 28, cyst n = 2, progressive ethmoidal hematoma [PEH] n = 2, traumatic n = 2, malignant neoplasia n = 2) were dominated by moderate to high numbers of neutrophilic granulocytes and moderate numbers of different epithelial cells, whereas samples from healthy sinuses revealed almost exclusively epithelial cells. Smears in dental-related sinusitis tended to contain more lytic cellular material than in other conditions. Horses with dental sinusitis also showed a higher intracellular and extracellular bacterial burden than horses with other underlying etiologies and healthy horses. The absence of bacteria in light microscopy did not exclude the evidence of pathogenic bacteria from bacterial culture in every case. Case numbers were too small to evaluate the diagnostic value for neoplastic conditions or PEH. In conclusion, cytological examination of secretions from the paranasal sinuses can provide an additional but limited ancillary diagnostic value in equine sinusitis.