Chest X-ray signs of feline infectious peritonitis in cats

Abstract

OBJECTIVES: The objective of this study was to describe thoracic radiographic findings and associated histopathological changes (where available) in cats with feline infectious peritonitis (FIP). METHODS: This was a retrospective descriptive study. Cats were included if they had a definitive diagnosis of FIP (based on histopathology and immunohistochemistry) or a presumptive diagnosis of FIP (based on case review by two veterinary internists), and contemporaneous orthogonal thoracic radiographs. Radiographs were reviewed retrospectively by a veterinary radiologist and veterinary radiology resident and assessed for the following: presence of pleural space disease; unstructured interstitial, bronchial, alveolar and/or nodular pulmonary patterns; lymphadenopathy; and cardiovascular abnormalities. Archived histopathologic specimens were reviewed by a veterinary pathologist. RESULTS: In total, 35 cats were included: 18 with definitive FIP and 17 with presumptive FIP. Radiographs were abnormal in 32/35 cats and normal in 3/35 cats. Pleural effusion was present in 13/35 cats and was either bilateral (11/13) or unilateral (2/13) in distribution. The lungs were radiographically abnormal in 25/35 cats, with the most common abnormality being an unstructured interstitial pattern (21/25), with bronchial (11/25) and alveolar (10/25) patterns less common. Pulmonary nodules were identified in 3/25 cats. Mixed pulmonary patterns were frequent (18/25). Sternal lymphadenopathy was present in 16/35 cats. An enlarged cardiac silhouette was noted in 6/35 cats, attributable to myocarditis (3/6), pericardial effusion (1/6), a high output state (1/6) or unrelated cardiomyopathy (1/6). Common histopathologic lesions included pulmonary edema (16/17), fibrinosuppurative pleuritis (13/17) and histiocytic vasculitis causing pneumonia (10/17); myocarditis (5/14); and lymphadenitis (2/2). Histologic lung changes were more common in patients with moderate to severe radiographic pulmonary changes. CONCLUSIONS AND RELEVANCE: Thoracic radiographic findings in cats with FIP may include variably distributed pleural effusion; interstitial, bronchial, and/or alveolar patterns; pulmonary nodules; lymphadenopathy; and cardiomegaly. FIP should be considered in cats with these radiographic changes and supportive clinical findings.