The initial investigations for suspected empyema remains chest X-ray, although it cannot differentiate an empyema from uninfected parapneumonic effusion. Ultrasound must be used to confirm the presence of a pleural fluid collection and can be used to estimate the size of the effusion, differentiate between free and loculated pleural fluid and guide thoracocentesis if necessary. Chest CT and MRI do not provide additional information in most cases and should therefore not be performed routinely. On a CT scan, empyema fluid most often has a radiodensity of about 0-20 Hounsfield units (HU), but gets over 30 HU when becoming more thickened with time.

The most often used "golden" criteria for empyema are pleural effusion with macroscopic presence of pus, a positive Gram stain or culture of pleural fluid, or a pleural fluid pH under 7.2 with normal peripheral blood pH. Clinical guidelines for adult patients therefore advocate diagnostic pleural fluid aspiration in patients with pleural effusion in association with sepsis or pneumonic illness. Because pleural effusion in the pediatric population is almost always parapneumonic and the need for chest tube drainage can be made on clinical grounds, British guidelines for the management of pleural infection in children do not recommend diagnostic pleural fluid sampling.

Blood and sputum culture has often already been performed in the setting of community acquired pneumonia needing hospitalization. It should however be noted that the micro-organism responsible for development of empyema is not necessarily the same as the organism causing the pneumonia, especially in adults. As already mentioned before, sensitivity of pleural fluid culture is generally low, often partly due to prior administration of antibiotics. It has been shown that culture yield can be increased from 44% to 69% if pleural fluid is injected into blood culture bottles (aerobic and anaerobic) immediately after aspiration. Furthermore, diagnostic rates can be improved for specific pathogens using polymerase chain reaction or antigen detection, especially for Streptococcus pneumoniae, Streptococcus pyogenes and Staphylococcus aureus. In a study including 78 children with pleural empyema, the causative micro-organism could be identified using direct culture of fresh pleural fluid in 45% of patients, with an additional 28% using PCR on pleural fluid of negative cultures. Pneumococcal antigen detection in pleural fluid samples by latex agglutination can also be useful for rapid diagnosis of pneumococcal empyema. In the previously noted study, positive and negative predictive value of pneumococcal antigen detection was 95% and 90%, respectively. However, despite the additional diagnostic value of these tests, PCR and antigen detection have limited value in determining treatment choice because of the lack of information on antibiotic resistance.

Proven empyema (as defined by the "golden" criteria mentioned earlier) is an indication for prompt chest tube drainage. This has been shown to improve resolution of the infection and shorten hospital admission. Data from a meta-analysis has shown that a pleural fluid pH of <7.2 is the most powerful indicator to predict the need for chest tube drainage in patients with non-purulent, culture negative fluid. Other indications for drainage include poor clinical progress during treatment with antibiotics alone and patients with a loculated pleural collection.

Because of the viscous, lumpy nature of infected pleural fluid, in combination with possible septation and loculation, it has been proposed that intrapleural fibrinolytic or mucolytic therapy might improve drainage and therefore might have a positive effect on the clinical outcome. Intrapleural fibrinolysis with urokinase decreased the need for surgery but there is a trend to increased serious side effects.

Approximately 15 to 40 percent of people require surgical drainage of the infected pleural space because of inadequate drainage due to clogging of the chest tube or loculated empyema. Patients should thus be considered for surgery if they have ongoing signs of sepsis in association with a persistent pleural collection despite drainage and antibiotics. Video-assisted thoracoscopic surgery (VATS) is used as a first-line therapy in many hospitals, although open thoracic drainage remains a frequently used alternative technique.

Raised inflammatory markers (high ESR, CRP) are common but nonspecific. Examination of the coughed up mucus is important in any lung infection and often reveals mixed bacterial flora. Transtracheal or transbronchial (via bronchoscopy) aspirates can also be cultured. Fiber optic bronchoscopy is often performed to exclude obstructive lesion; it also helps in bronchial drainage of pus.

A parapneumonic effusion is a type of pleural effusion that arises as a result of a pneumonia, lung abscess, or bronchiectasis. There are three types of parapneumonic effusions: uncomplicated effusions, complicated effusions, and empyema. Uncomplicated effusions generally respond well to appropriate antibiotic treatment.

- Diagnosis

The criteria for a complicated parapneumonic effusion include the presence of pus, Gram stain–positive or culture-positive pleural fluid, pleural fluid pH <7.20, and pleural fluid LDH that is greater than three times the upper limit of normal of serum LDH. Diagnostic techniques available include plain film chest x-ray, computed tomography (CT), and ultrasound. Ultrasound can be useful in differentiating between empyema and other transudative and exudative effusions due in part to relative echogenicity of different organs such as the liver (often isoechogenic with empyema).

- Treatment

Appropriate management includes chest tube drainage (tube thoracostomy). Treatment of empyemas includes antibiotics, complete pleural fluid drainage, and reexpansion of the lung.

Other treatments include the use of decortication.

Most cases respond to antibiotics and prognosis is usually excellent unless there is a debilitating underlying condition. Mortality from lung abscess alone is around 5% and is improving.

An empyema (from Greek ἐμπύημα, "abscess") 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.

For those with a history of intravenous drug use, an X-ray is recommended before treatment to verify that no needle fragments are present. In this population if there is also a fever present infectious endocarditis should be considered.

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

Abscesses should be differentiated from empyemas, which are accumulations of pus in a preexisting rather than a newly formed anatomical cavity.

Other conditions that can cause similar symptoms include: cellulitis, a sebaceous cyst and necrotising fasciitis. Cellulitis typically also has an erythematous reaction, but does not confer any purulent drainage.

In some cases, abscesses may be prevented by draining an existing pseudocyst which is likely to become inflamed. However, in most cases the developing of abscesses cannot be prevented.

Most patients who develop pancreatic abscesses have had pancreatitis, so a complete medical history is required as a first step in diagnosing abscesses. On the other hand, a white blood cell count is the only laboratory test that may indicate the presence of an abscess.

Some of the imaging tests are more commonly used to diagnose this condition. Abdominal CT scans, MRIs and ultrasounds are helpful in providing clear images of the inside of the abdomen and successfully used in the diagnosing process. These tests may reveal the presence of infected necrosis which has not yet developed into an abscess and as a result, doctors usually order repeated imaging tests in patients with acute pancreatitis whose abdominal pain worsens and who develop signs of abdominal obstruction. Also, it is recommended that patients who have a prolonged clinical response are tested repeatedly as a prevention method to avoid the development of an abscess that may rupture.

Diagnosis is usually based on the symptoms. Medical imaging may be done to rule out complications. Medical imaging may include CT scan or MRI.

Treatment of hydrothorax is difficult for several reasons. The underlying condition needs to be corrected; however, often the source of the hydrothorax is end stage liver disease and correctable only by transplant. Chest tube placement should not occur. Other measures such as a TIPS procedure are more effective as they treat the cause of the hydrothorax, but have complications such as worsened hepatic encephalopathy.

Possible complications include the horse becoming a chronic carrier of the disease, asphyxia due to enlarged lymph nodes compressing the larynx or windpipe, bastard strangles (spreading to other areas of the body), pneumonia, guttural pouch filled with pus, abscesses, purpura haemorrhagica, and heart disease. The average length for the course of this disease is 23 days.

The diagnosis of mastoiditis is clinical—based on the medical history and physical examination. Imaging studies provide additional information; The standard method of diagnosis is via MRI scan although a CT scan is a common alternative as it gives a clearer and more useful image to see how close the damage may have gotten to the brain and facial nerves. Planar (2-D) X-rays are not as useful. If there is drainage, it is often sent for culture, although this will often be negative if the patient has begun taking antibiotics. Exploratory surgery is often used as a last resort method of diagnosis to see the mastoid and surrounding areas.

Spinal epidural abscess (SEA) is a collection of pus or inflammatory granulation between the dura mater and the vertebral column. Currently the annual incidence rate of SEAs is estimated to be 2.5-3 per 10,000 hospital admissions. Incidence of SEA is on the rise, due to factors such as an aging population, increase in use of invasive spinal instrumentation, growing number of patients with risk factors such as diabetes and intravenous drug use. SEAs are more common in posterior than anterior areas, and the most common location is the thoracolumbar area, where epidural space is larger and contains more fat tissue.

SEAs are more common in males, and can occur in all ages, although highest prevalence is during the fifth and seventh decades of life.

The pus can be removed by a number of methods including needle aspiration, incision and drainage, and tonsillectomy.

Treatment can also be given while a patient is under anesthesia, but this is usually reserved for children or anxious patients. Tonsillectomy can be indicated if a patient has recurring peritonsillar abscesses or a history of tonsillitis. For patients with their first peritonsillar abscess most ENT-surgeons prefer to "wait and observe" before recommending tonsillectomy.

Both intramuscular and intranasal vaccines are available. Isolation of new horses for 4 to 6 weeks, immediate isolation of infected horses, and disinfection of stalls, water buckets, feed troughs, and other equipment will help prevent the spread of strangles. As with any contagious disease, handwashing is a simple and effective tool.

Hydrothorax is a type of pleural effusion in which transudate accumulates in the pleural cavity. This condition is most likely to develop secondary to congestive heart failure, following an increase in hydrostatic pressure within the lungs. More rarely, hydrothorax can develop in patients with cirrhosis or ascites. Hepatic hydrothorax is often difficult to manage in end-stage liver failure and often fails to respond to therapy.

Pleural effusions may also develop following the accumulation of other fluids within the pleural cavity; if the fluid is blood it is known as hemothorax (as in major chest injuries), if the fluid is pus it is known as pyothorax (resulting from chest infections), and if the fluid is lymph it is known as chylothorax (resulting from rupture of the thoracic duct).

Urinothorax ("pl". urinothoraces) means urine in the fluid-filled cavity that surrounds the lungs. It is a rare cause of pleural effusion secondary to obstructive uropathy whereby urine forms a collection in the pleural cavity. The urine arrives in the pleural space either retroperitoneally under the posterior diaphragm, or via the retroperitoneal lymphatics. It remains a rare, possibly under-diagnosed, differential in the case of transudative pleural effusion.

Handa et al., described 47 cases between 1967 and 2007, noting that it was more prevalent in males, generally ipsilateral to the obstruction, and in most cases relieved by clearance of the obstruction.

A cranial epidural abscess involves pus and granulation tissue accumulation in between the dura mater and cranial bone. These typically arise (along with osteomyelitis of a cranial bone) from infections of the ear or paranasal sinuses. They rarely can be caused by distant infection or an infected cerebral venous sinus thrombosis. Staphylococcus aureus is the most common pathogen. Symptoms include pain at the forehead or ear, pus draining from the ear or sinuses, tenderness overlying the infectious site, fever, neck stiffness, and in rare cases focal seizures. Treatment requires a combination of antibiotics and surgical removal of infected bone.

Treatment for a nasal septal abscess is similar to that of other bacterial infections. Aggressive broad spectrum antibiotics may be used after the infected area has been drained of fluids.

The prevalence of pulmonary interstitial emphysema widely varies with the population studied. In a 1987 study 3% of infants admitted to the neonatal intensive care unit (NICU) developed pulmonary interstitial emphysema.

The main goal of treatment is to remove the cause of the phlegmonous process in order to achieve effective treatment and prevention of recidives.

If the patient's condition is mild and signs of inflammatory process are present without signs of infiltrates, then conservative treatment with antibiotics is sufficient.

If the patient's condition is severe, however, immediate operation is usually necessary with application of drainage system. All of these are done under general anaesthesia. During operation, the cavity or place of phlegmonous process are washed with antiseptic, antibiotic solutions and proteolyic ferments.

In post-operative period, patients are treated with intravenous antibiotics, haemosorbtion, vitaminotherapy. Additionally, the use of i/v or i/m antistaphylococci γ-globulin or anatoxin can be taken as immunotherapy.

During operation of phlegmon dissection at any location, it is important:

1. to avoid spreading of pus during operation;

2. to take into account the cosmetic value of the operating site, especially when treating phlegmmonous process of the face; and

3. to avoid damaging nerves.

Studies reflecting international frequency demonstrated that 2-3% of all infants in NICUs develop pulmonary interstitial emphysema. When limiting the population studied to premature infants, this frequency increases to 20-30%, with the highest frequencies occurring in infants weighing fewer than 1000 g.