Retrospective Evaluation of the Causes and Fluid Characteristics of Cavitary Effusions in Dogs and Cats

Abstract

Background: The relationship between fluid characteristics and cause of cavitary effusions is incompletely characterized.

Hypothesis/objectives: Describe fluid characteristics and cytologic classification of cavitary effusions in dogs and cats.

Animals: A total of 269 dogs and 107 cats with cytologic fluid analysis of cavitary effusion.

Methods: Retrospective medical record review (2016-2020). Differences among groups were assessed using Kruskal-Wallis testing with post hoc pairwise Dunn's or Fisher's Exact testing.

Results: In dogs, peritoneal transudates most frequently were caused by decreased oncotic pressure (DOP; 63%, p < 0.001) and modified transudates by increased hydrostatic pressure (IHP; 41%, p < 0.001). Peritoneal exudates more frequently were caused by increased vascular permeability (IVP; 40%), ruptured viscera (35%), or neoplasia (23%) compared with IHP or DOP (p < 0.01 for all). Pleural transudates in dogs most frequently were caused by DOP (79%, p < 0.001) and modified transudates by IHP (33%) or neoplasia (29%). Pleural exudates were more likely to be caused by neoplasia (52%) or IVP (36%) compared with IHP or DOP (p < 0.001). In cats, peritoneal effusions commonly were caused by IVP or neoplasia, and pleural effusions by IHP or neoplasia. No statistical relationship was found between cytologic category and cause of effusion in cats.

Conclusions and clinical importance: Cytologic classification and fluid characteristics are most predictive of disease process in peritoneal effusions in dogs, whereas effusions in cats have substantial overlap across causes.

Keywords: canine; cardiology; clinical pathology; cytology; feline; pericardial effusion; peritoneal; pleural effusion.