A continuum. Empyema is a severe infection in the chest in which pus accumulates within the pleural space. Also known as pleural empyema, empyema thoracis and pyothorax. It will often develop as a consequence of a pneumonia. A fluid collection forms (parapneumonic effusion) and this fluid becomes infected. The treatment is to drain the pus, re-expand lung, and treat underlying infection. http://goo.gl/5dncp.