An empyema () 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". 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

External links

Shen, K. Robert; Bribriesco, Alejandro; Crabtree, Traves; Denlinger, Chad; Eby, Joshua; Eiken, Patrick; Jones, David R.; Keshavjee, Shaf; Maldonado, Fabien; Paul, Subroto; Kozower, Benjamin (February 2017). "The American Association for Thoracic Surgery consensus guidelines for the management of empyema". The Journal of Thoracic and Cardiovascular Surgery. 153 (6): e129–e146. doi:10.1016/j.jtcvs.2017.01.030. PMID 28274565.
Less common sites include the kidneys, intestines, and eyes. Risk factors
Risk factors for thromboembolism, the major cause of arterial embolism, include disturbed blood flow (such as in atrial fibrillation and mitral stenosis), injury or damage to an artery wall, and hypercoagulability (such as increased platelet count). Mitral stenosis poses a high risk of forming emboli which may travel to the brain and cause stroke. Endocarditis increases the risk for thromboembolism, by a mixture of the factors above. Atherosclerosis in the aorta and other large blood vessels is a common risk factor, both for thromboembolism and cholesterol embolism. The legs and feet are major impact sites for these types. Thus, risk factors for atherosclerosis are risk factors for arterial embolisation as well:

advanced age
cigarette smoking
hypertension (high blood pressure)
obesity
hyperlipidemia, e.g. hypercholesterolemia, hypertriglyceridemia, elevated lipoprotein (a) or apolipoprotein B, or decreased levels of HDL cholesterol)
diabetes mellitus
Sedentary lifestyle
stressOther important risk factors for arterial embolism include:

recent surgery (both for thromboembolism and air embolism)
previous stroke or cardiovascular disease
a history of long-term intravenous therapy (for air embolism)
Bone fracture (for fat embolism)A septal defect of the heart makes it possible for paradoxical embolization, which happens when a clot in a vein enters the right side of the heart and passes through a hole into the left side. The clot can then move to an artery and cause arterial embolisation. Pathophysiology
An arterial embolism is caused by one or more emboli getting stuck in an artery and blocking blood flow, causing ischemia, possibly resulting in infarction with tissue death (necrosis).