Empyem

Empyema is the accumulation of pus within a preexisting anatomical cavity due to infection. The term most often refers to pleural empyema, an infected pleural effusion, but it can occur in other spaces such as the peritoneal cavity (abdominal empyema) or the brain (subdural empyema). Pleural empyema usually follows pneumonia or thoracic infection and may develop after chest surgery or trauma.

Pathophysiology involves an inflammatory exudate that becomes infected and trapped within the pleural space. Empyema progresses through three overlapping stages: an initial exudative phase with free-flowing pleural fluid; a fibrinopurulent phase with loculations and fibrin deposition; and an organizing phase in which a thick pleural peel restricts lung expansion and may require surgery.

Clinical features include fever, night sweats, pleuritic chest pain, dyspnea, and productive cough. Exam may show dullness to percussion and decreased breath sounds. Diagnosis uses imaging (ultrasound or CT) to identify loculations and pleural fluid analysis after thoracentesis. Fluid pH is often below 7.2, glucose below 60 mg/dL, and LDH elevated; neutrophilia is typical. Gram stain and culture of the fluid, along with blood cultures, aid identification. Imaging guides drainage.

Treatment requires antibiotics and drainage. Early stages may respond to thoracentesis; most require chest tube drainage. Intrapleural fibrinolytics (tPA and DNase) can help break loculations; organized disease may need video-assisted thoracoscopic surgery or open decortication. Prognosis improves with prompt drainage and appropriate antibiotic therapy; mortality varies with age and comorbidity.