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. 2025 Sep-Oct;39(5):e70205.
doi: 10.1111/jvim.70205.

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

Samantha Sotillo  1 , Austin K Viall  2 , Jean-Sebastien Palerme  1 , Jessica L Ward  1
Affiliations

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

Samantha Sotillo et al. J Vet Intern Med. 2025 Sep-Oct.

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.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Comparison of effusion characteristics among disease process categories within specific body cavities for dogs. For all box and whisker plots, the median is represented by a horizontal line, boxes indicate interquartile range, and whiskers indicate range. DOP, decreased oncotic pressure; IHP, increased hydrostatic pressure; IVP, increased vascular permeability; LMN, large mononuclear cells.
FIGURE 2
FIGURE 2
Comparison of effusion characteristics among disease process categories within specific body cavities for cats. For all box and whisker plots, the median is represented by a horizontal line, boxes indicate interquartile range, and whiskers indicate range. IHP, increased hydrostatic pressure; IVP, increased vascular permeability.
FIGURE 3
FIGURE 3
Percentage of cytologic classifications (transudate, modified transudate, exudate, or hemorrhage) caused by various underlying causes of effusion in dogs and cats. Numbers within each bar indicate absolute numbers of animals with each cytologic classification for each cause; see Tables 2, 3, 4, 5, 6 for detailed breakdown.
FIGURE 4
FIGURE 4
Comparison of effusion characteristics between pleural and peritoneal cavities within a specific disease process category in dogs. For all box and whisker plots, the median is represented by a horizontal line, boxes indicate interquartile range, and whiskers indicate range.
FIGURE 5
FIGURE 5
Comparison of effusion characteristics between pleural and peritoneal cavities within a specific disease process category in cats. For all box and whisker plots, the median is represented by a horizontal line, boxes indicate interquartile range, and whiskers indicate range.
FIGURE 6
FIGURE 6
Comparison of effusion characteristics between dogs and cats for a given body cavity and disease process category. For all box and whisker plots, the median is represented by a horizontal line, boxes indicate interquartile range, and whiskers indicate range.
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