Lung abscesses have a slow, insidious presentation, usually developing from 1-2 weeks after the initial aspiration event. Empyema is defined as pus in the pleural space. It is typically a complication of pneumonia. It can also arise, however, from penetrating chest trauma, esophageal rupture, or inoculation of the pleural cavity after thoracentesis or chest tube placement. An empyema can also occur from extension of a subdiaphragmatic or paravertebral abscess.
Lung abscesses involve the lung parenchyma while empyema involves the pleural space.
Many patients give a history of a recent diagnosis and treatment for pneumonia. A recent history of penetrating chest trauma should raise a clinical suspicion for empyema. Patients complain of a cough productive of bloody sputum and frequently with a fetid odor or appearance. The microbiology of lung abscesses and empyema is typically polymicrobial oral flora, including Bacteroides species, Fusobacterium species, and Peptostreptococcus . Pseudomonas , Klebsiella , Staphylococcus aureus , Streptococcus pneumoniae , Nocardia , and fungal species are less commonly seen.