Empyema

An empyema (from Greek ἐμπύημα, "abscess") is a collection of pus within a naturally existing anatomical cavity. For example, pleural empyema is empyema of the pleural cavity. It must be differentiated from an abscess, which is a collection of pus in a newly formed cavity.

Classification
In human medicine, empyema occurs in:
 * the pleural cavity (pleural empyema also known as pyothorax)
 * the thoracic cavity
 * the uterus (pyometra)
 * the appendix (appendicitis)
 * the meninges (subdural empyema)
 * the joints (septic arthritis)
 * the gallbladder