Morphological patterns of pneumonia in free-roaming cats: a necropsy and histopathological study.

Background: Pneumonia is a significant cause of morbidity and mortality in free-roaming domestic cats, particularly when associated with infectious agents and underlying systemic conditions. Post-mortem studies remain essential for characterizing pulmonary lesions and refining etiological interpretation, especially in under-monitored populations with limited or absent antemortem clinical information. In this context, recognition of morphologic patterns may help pathologists interpret pulmonary lesions more accurately and may provide clinicians with useful clinicopathological insights into concurrent disease, differential diagnoses, and likely causes of death. Objectives: To characterize the gross and histopathological patterns of pneumonia in free-roaming cats submitted for necropsy, to identify associated infectious agents when available, and to assess the clinicopathological relevance of pneumonia to outcome in a population in which clinical history is often incomplete. Methods: A retrospective necropsy-based study was conducted on feline pneumonia cases examined between 2014 and 2024. Gross and histopathological lung findings were reviewed and classified according to established morphological patterns of pneumonia. Available clinical records were also reviewed to assess antemortem clinical context, type of death, and the inferred relevance of pneumonia to outcome. Ancillary microbiological testing, including bacterial culture, was performed when lung samples were available. Results: Of 289 necropsied domestic cats, pneumonia was confirmed in 49 free-roaming cats. Most animals died spontaneously (47/49; 95.9%), whereas euthanasia was recorded in two cases (2/49; 4.1%). Antemortem clinical information was available for 31/49 cats (63.3%). The most frequent major morphologic category was bronchopneumonia (32/49; 65.3%), including 26 cases of conventional bronchopneumonia, three of aspiration pneumonia, and three of pleuropneumonia. Interstitial pneumonia/interstitial lung disease accounted for 8/49 cases (16.3%), including six cases of interstitial pneumonia and two of bronchointerstitial pneumonia. Pyogranulomatous pneumonia was identified in 5/49 cases (10.2%), granulomatous pneumonia in 3/49 (6.1%), and embolic pneumonia in 1/49 (2.0%). Pneumonia was interpreted as the primary cause of death or euthanasia in 30 cases (61.2%), a contributing factor in 15 (30.6%), and an incidental finding in 4 (8.2%). Infectious agents were heterogeneous, and bacterial growth was detected in a subset of cases, with Conclusion: This study highlights the morphological diversity of feline pneumonia and reinforces the central role of post-mortem pathological examination in its classification and interpretation. Integration of gross, histopathological, clinical, and ancillary microbiological findings improves interpretation of the morphologic spectrum, etiologic associations, and clinicopathological relevance of feline pneumonia, particularly in free-roaming cats with incomplete clinical histories and frequent concurrent systemic disease.