Cytological and pathological methods in the differential diagnosis of exudative infectious peritonitis form in cats

The article presents the results of a comprehensive pathological and cytological examination of cats with suspected exudative form of feline infectious peritonitis (FIP). The aim of the study was to investigate the diagnostic informativeness of cytological and pathological examination for the differentiation of IPC from other causes of ascites. A retrospective analysis of 135 clinical cases of cats with effusion was performed. The results showed that among the retrospectively studied cases of ascites, UIC was not the leading cause, and purulent, neoplastic or reactive processes were diagnosed in most cases. A comparative analysis of pathologic changes revealed characteristic macromorphologic features that allow distinguishing between UC, chronic purulent peritonitis, and metastatic lesions in the neoplastic process. UTI is accompanied by yellowish viscous effusion, small grayish granulomas on the serous membranes, while purulent peritonitis is dominated by a massive fibrinous-purulent layer, and neoplasia is characterized by tumor masses and nodal metastases in the lymph nodes and internal organs. Cytologic examination of the effusion was highly informative in identifying typical patterns: the combination of a weakly basophilic protein background with crystallization patterns and the absence of bacteria indicated the likelihood of UC; the predominance of degenerative neutrophils and bacteria - purulent peritonitis; and multicellularity, lymphocytic infiltration with atypical cells - lymphoma. In the samples of abdominal effusion from cats that were examined cytologically, signs of various variants of pyogranulomatous inflammation prevailed, one of the four samples could be defined as typical of UTI, the other three had signs of bacterial infection, which determined the cytological picture. The data obtained confirm that none of the morphological methods is sufficient on its own, but their combined use can improve diagnostic accuracy. Morphological evaluation, both in vivo (cytological) and postmortem (pathological), can be informative for differential diagnosis and is an important component of the comprehensive diagnosis of cats with ascites, in particular in the context of suspected UIC. Key words: ascites, macrophages, mesothelio cytes, exudate, cytologic analysis.