Pericardial-diaphragmatic malformation with intrapericardial diaphragmatic eventration in a cat

A 3-month-old intact male domestic shorthair kitten was evaluated for progressive, recurrent pericardial effusion. Computed tomography (CT) showed marked pericardial effusion with diffuse pericardial thickening and an apparent incomplete pericardial closure. Portions of the left medial and quadrate liver lobes and the gallbladder protruded cranially into the pericardial space and were encased by a thick, contrast-enhancing fibrous layer. These findings were initially interpreted as atypical peritoneopericardial diaphragmatic hernia (PPDH). Due to acute clinical deterioration, the kitten was euthanized. Necropsy and histology confirmed severe necrotizing pericarditis and epicarditis, incomplete pericardial closure, and ventral midline diaphragmatic eventration with intrapericardial protrusion of liver and gallbladder. This collection of findings supported a diagnosis of diaphragmatic eventration, forming a fibrous cupola contiguous with the pericardium, which can mimic PPDH on imaging. Key clinical message: To the authors' knowledge, the combination of CT findings and histologic confirmation of diaphragmatic eventration with incomplete closure of the pericardium has not been previously reported. When CT shows a pericardium continuous with the diaphragm and a fibrous cupola encasing intrapericardial protruded abdominal organs, eventration should be included in the differential diagnosis, in addition to PPDH.