empyema empyema an empyema (/ˌɛmpaɪˈiːmə/) is a collection or gathering 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. the term is from greek ἐμπύημα, "abscess". empyemaspecialtypulmonology, infectious disease classification 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