A lung abscess is a cavity with a well-defined wall that develops in the lung due to microbial infection. This most commonly occurs with polymicrobial aerobic and anerobic infections related to aspiration pneumonia. Lung abscess may also be related to necrotizing pneumonia from aerobic organisms (eg, Staphylococcus aureus, Pseudomonas aeruginosa), septic emboli, or bronchial obstruction (eg, tumor). Most patients respond to appropriate antimicrobial therapy. However, catheter or surgical drainage may be needed if initial therapy is ineffective or the patient has complications such as extension into the pleural space (empyema). Pleural effusion is a manifestation of various underlying pathologies with a broad differential diagnosis. Defining the etiology of pleural effusion is critical for appropriate management. Thoracentesis should be considered for all pleural effusions associated with pneumonia. Parapneumonic effusions and empyema should be treated with prompt initiation of antibiotics and drainage of infected pleural fluid.

Case 1. DB is a 36-year-old man brought to the emergency department by paramedics. He has alcohol use disorder, housing insecurity, and a 20-pack-year smoking history. He has a cough producing dark, foul-smelling sputum that has been worsening for 1 week and is now associated with midsternal and left upper back pain. DB reports weakness, dyspnea, and chills but no hemoptysis. His temperature is 102°F (38.9°C), pulse is 106 beats/min, blood pressure is 145/89 mm Hg, and pulse oximetry is 93% on room air. Auscultation reveals coarse rales in the left middle to lower lung fields and normal heart sounds. His white blood cell count is 16,000/μL (16 × 10⁹ /L) with a normal differential. Chest radiography shows a 4-cm, left midlung cavitary lesion with a definite air-fluid level.