Just a gorgeous paper....

The Pathogenesis of Paraesophageal Empyema in Dogs and Constancy of Radiographic and Computed Tomography Signs Are Linked to Involvement of the Mediastinal Serous Cavity

Karine Gendron, Sean P. McDonough, James A. Flanders, May Tse, Peter V. Scrivani

Background
Paraesophageal empyema is an uncommon but serious condition in dogs, characterized by the accumulation of purulent material in the mediastinal serous cavity. This space, located in the caudal mediastinum adjacent to the esophagus, is a mesothelial-lined extension of the omental bursa. The study aimed to describe the imaging features of paraesophageal empyema on computed tomography (CT), evaluate the anatomic basis for the condition, and explore potential pathogenic mechanisms, including possible associations with pulmonary disease or foreign body migration.

Methods
This study consisted of an anatomic investigation using cadaver dissections and histology, a retrospective case series of five dogs with confirmed paraesophageal empyema, and a literature review of similar cases. Histological analysis confirmed the presence of a mesothelial lining in the mediastinal serous cavity. CT scans were analyzed to assess lesion size, location, attenuation, and involvement of adjacent structures. Surgical findings, bacterial cultures, and histopathology were reviewed for all cases.

Results
CT findings were consistent across all dogs, showing a fluid-filled, well-defined lesion in the caudal mediastinum, always located to the right of the esophagus. The lesions displayed minimal contrast enhancement, indicating a chronic inflammatory process. Four of five dogs had concurrent accessory lung lobe consolidation, and two had macroscopic plant material in the empyema cavity or mediastinum. Histology confirmed chronic pyogranulomatous inflammation, with no evidence of esophageal perforation. Review of prior literature identified 12 additional cases with similar imaging and surgical findings.

Limitations
The study was limited by its small sample size and retrospective design. The precise mechanism leading to empyema development remains unclear, though the findings suggest a potential link to pulmonary disease or migrating foreign bodies. Additionally, surgical exploration may not have detected small esophageal perforations.

Conclusions
Paraesophageal empyema in dogs appears to originate from inflammatory processes within the mediastinal serous cavity, likely secondary to pulmonary disease or foreign body migration rather than esophageal perforation. Recognition of the mediastinal serous cavity as an anatomical structure is important for accurate diagnosis and surgical planning. CT is valuable for lesion localization and characterization, aiding in the differentiation from other mediastinal abnormalities.

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