Empyema necessitatis.

Empyema necessitatis is the accumulation of pus in a small space in the pleural cavity, with subsequent rupture of the purulent material into the surrounding soft tissue. Drainage may occur into the breast, bronchus, mediastinum, esophagus, diaphragm, pericardium or retroperitoneum. Pus may even reach the flank, groin or thigh. Before antibiotics became available, empyema necessitatis was a complication of tuberculosis, fungal infections and various forms of pneumonia. Silent infections due to tuberculosis or fungus can still present as empyema necessitatis, even in healthy young adults.