Bacterial pneumonia with associated pleural empyema is the most common cause of pleural effusion found in the pediatric population. Parapneumonic effusions are predominately exudative and occur in as many as 50-70% of patients admitted with a complicated pneumonia.
See the image below.
Most parapneumonic effusions treated with the appropriate antimicrobials of sufficient duration resolve without the development of complications or sequelae. The series of radiographs represent a patient treated with thoracentesis alone. Figure A illustrates the patient at presentation. Note the amount of fluid present. In Figure B, the radiograph demonstrates progression of the pleural fluid accumulation with further airspace disease and scoliosis noted. Despite the radiographic evidence of disease progression, the patient was clinically improving. Figure C illustrates the radiograph at follow-up, 6 months following completion of therapy. Resolution of the parapneumonic effusion with no evidence of pleural thickening or fibrosis occurred.
The pulmonary infections of these patients extend into the pleural space and require more extensive therapy, with associated increased morbidity and extended hospital stay. Involvement of the pleural space with pulmonary infections has been recognized since ancient times. Aristotle identified the increased morbidity and mortality associated with empyema and described drainage of empyema fluid with incision. The practice of surgical drainage as part of therapy for empyema has continued into the era of modern medicine. In his 1901 text, The Principles and Practice of Medicine, Sir William Osler, MD, stated that empyema should be treated as an ordinary abscess, “with incision and drainage.”
Of note, Osler underwent a rib resection for his own postpneumonic empyema, from which he ultimately expired.
Complicated parapneumonic effusions are appearing more frequently by most accounts, with reported increases in incidence rates in both in Europe and the United States. In England, the rate of admission with a diagnosis of empyema increased over the last decade, most notably in children aged 1-4 years. In addition, the identification of Streptococcus pneumoniae as the primary pathogen has also been reported, both in both the United States and abroad.
Whereas the overall rate of parapneumonic effusions may have stabilized over the last decade, the rate of bacterial resistance, specifically methicillin-resistant Staphylococcus aureus, has predominated.