Pleural Infection as the First Presentation of a Large Retroperitoneal Abscess

Empyema originating from a retroperitoneal source is rare due to the anatomical separation between the retroperitoneal and pleural spaces. We report the case of an 81-year-old man who presented with pleuritic chest pain following empirical antibiotic treatment for a urinary tract infection. Imaging revealed a large retroperitoneal gas-containing fluid collection and a left-sided loculated pleural effusion with a small pneumothorax. Pleural and retroperitoneal collection fluid both grew Escherichia coli suggestive of trans-diaphragmatic spread. A large hiatal hernia, structural defects of the hemidiaphragm and a Bochdalek hernia may also have been contributing factors. The patient improved with systemic antibiotics, percutaneous drainage of both collections and intrapleural administration of low dose tPA/DNase therapy. This case underscores the importance of considering extra-thoracic (especially abdominal) sources, especially in patients with structural diaphragmatic abnormalities.