Parapneumonic effusion	Imaging characteristics	Aspirate characteristics	Therapy overview
Minimal	Lateral anterior chest radiography with costophrenic angle blunting, minimal size on POCUS or CT (estimated < 100 mL, < 10 mm fluid in height on lateral decubitus film)	Unknown	Thoracentesis usually not indicated; antibiotic therapy with close monitoring
Simple	Effusion without complex features on POCUS or CT (free-flowing and without septations or loculations); often a small, unilateral effusion (estimated size 100 mL, > 20 mm in height on CT or POCUS, > 10 mm on lateral decubitus film)	Gram negative, culture negative, pH > 7.2, and glucose > 60 mg per dL (3.33 mmol per L)	Thoracentesis is indicated; medical management with antibiotics; monitoring for exacerbations, increasing effusion size, and new complex features on repeat imaging
Complicated	Variable in size—any large (more than one-half of the hemithorax on chest radiography) effusion is suspect; septations and loculations on POCUS; loculation and thickened parietal pleura on contrast CT; absence of these findings on imaging does not rule out a complicated parapneumonic effusion	Gram positive, culture positive, or pH < 7.2; glucose < 40 mg per dL (2.22 mmol per L), or purulence on initial aspirate (empyema)	Thoracentesis plus catheter or chest tube drainage; tissue plasminogen activator/deoxyribonuclease therapy; medical thoracoscopy and video-assisted thoracoscopic surgery for decortication; expanded antibiotic coverage and duration