The clinical presentation of both the adult and pediatric patient with pleural empyema depends upon several factors, including the causative micro-organism. Most cases present themselves in the setting of a pneumonia, although up to one third of patients do not have clinical signs of pneumonia and as many as 25% of cases are associated with trauma (including surgery). Typical symptoms include cough, chest pain, shortness of breath and fever.

Pleural empyema is a collection of pus in the pleural cavity caused by microorganisms, usually bacteria. Often it happens in the context of a pneumonia, injury, or chest surgery. It is one of various kinds of pleural effusion. There are three stages: exudative, when there is an increase in pleural fluid with or without the presence of pus; fibrinopurulent, when fibrous septa form localized pus pockets; and the final organizing stage, when there is scarring of the pleura membranes with possible inability of the lung to expand. Simple pleural effusions occur in up to 40% of bacterial pneumonias. They are usually small and resolve with appropriate antibiotic therapy. If however an empyema develops additional intervention is required.

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

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.

Onset of symptoms is often gradual, but in necrotizing staphylococcal or gram-negative bacillary pneumonias patients can be acutely ill. Cough, fever with shivering, and night sweats are often present. Cough can be productive of foul smelling purulent mucus (≈70%) or less frequently with blood in one third of cases). Affected individuals may also complain of chest pain, shortness of breath, lethargy and other features of chronic illness.

Those with a lung abscess are generally cachectic at presentation. Finger clubbing is present in one third of patients. Dental decay is common especially in alcoholics and children. On examination of the chest there will be features of consolidation such as localized dullness on percussion and bronchial breath sounds.

Rare nowadays but include spread of infection to other lung segments, bronchiectasis, empyema, and bacteremia with metastatic infection such as brain abscess.

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.

Abscesses may occur in any kind of solid tissue but most frequently on skin surface (where they may be superficial pustules (boils) or deep skin abscesses), in the lungs, brain, teeth, kidneys, and tonsils. Major complications are spreading of the abscess material to adjacent or remote tissues, and extensive regional tissue death (gangrene).

The main symptoms and signs of a skin abscess are redness, heat, swelling, pain, and loss of function. There may also be high temperature (fever) and chills.

An internal abscess is more difficult to identify, but signs include pain in the affected area, a high temperature, and generally feeling unwell.

Internal abscesses rarely heal themselves, so prompt medical attention is indicated if such an abscess is suspected.

An abscess could potentially be fatal (although this is rare) if it compresses vital structures such as the trachea in the context of a deep neck abscess.

If superficial, abscesses may be fluctuant when palpated. This is a wave-like motion that is caused by movement of the pus inside the abscess.

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.

An "incisional abscess" is one that develops as a complication secondary to a surgical incision. It presents as redness and warmth at the margins of the incision with purulent drainage from it. If the diagnosis is uncertain, the wound should be aspirated with a needle, with aspiration of pus confirming the diagnosis and availing for Gram stain and bacterial culture.

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.

Signs that consolidation may have occurred include:

- Expansion of the thorax on inspiration is reduced on the affected side

- Vocal fremitus is increased on the side with consolidation

- Percussion is dull in affected area

- Breath sounds are bronchial

- Possible medium, late, or pan-inspiratory crackles

- Vocal resonance is increased. Here, the patient's voice (or whisper, as in whispered pectoriloquy) can be heard more clearly when there is consolidation, as opposed to in the healthy lung where speech sounds muffled.

- A pleural rub may be present.

- A lower expected Pa02 than calculated in the alveolar gas equation

Patients with pancreatic abscesses may experience abdominal pain, chills and fever or the inability to eat. Whereas some patients present an abdominal mass, others do not. Nausea and vomiting may also occur.

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.

An unremoved infected abscess may lead to sepsis. Also, multiple abscesses may occur. Other complications may include fistula formation and recurrent pancreatitis.

Unlike tonsillitis, which is more common in the children, PTA has a more even age spread, from children to adults. Symptoms start appearing two to eight days before the formation of an abscess. A progressively severe sore throat on one side and pain during swallowing (odynophagia) usually are the earliest symptoms. As the abscess develops, persistent pain in the peritonsillar area, fever, a general sense of feeling unwell, headache and a distortion of vowels informally known as "hot potato voice" may appear. Neck pain associated with tender, swollen lymph nodes, referred ear pain and foul breath are also common. While these signs may be present in tonsillitis itself, a PTA should be specifically considered if there is limited ability to open the mouth (trismus).

Physical signs of a peritonsillar abscess include redness and swelling in the tonsillar area of the affected side and swelling of the jugulodigastric lymph nodes. The uvula may be displaced towards the unaffected side.

A pulmonary consolidation is a region of (normally compressible) lung tissue that has filled with liquid, a condition marked by induration (swelling or hardening of normally soft tissue) of a normally aerated lung. It is considered a radiologic sign. Consolidation occurs through accumulation of inflammatory cellular exudate in the alveoli and adjoining ducts. Simply, it is defined as alveolar space that contains liquid instead of gas. The liquid can be pulmonary edema, inflammatory exudate, pus, inhaled water, or blood (from bronchial tree or hemorrhage from a pulmonary artery). It must be present to diagnose pneumonia: the signs of lobar pneumonia are characteristic and clinically referred to as consolidation.

Phlegmon is a spreading diffuse inflammatory process with formation of purulent exudate (the suppuration of pus). This is the result of acute purulent inflammation which may be related to bacterial infection; however, the term 'phlegmon' (from Greek 'phlegmone', inflammation) mostly refers to a walled-off inflammatory mass without bacterial infection, one that may be palpable on physical examination.

An example would be phlegmon of diverticulitis. In this case a patient would present to the emergency department with left lower-quadrant abdominal tenderness, and the diagnosis of sigmoid diverticulitis would be high on the differential diagnosis, yet the best test to confirm it would be CT scan.

Another example, phlegmon affecting the spine, is known as spondylodiscitis and is associated with endplate destruction and loss of disc height. In adults, the bone marrow is affected first, while in children, the disease starts in the disc itself and spreads rapidly to the adjacent vertebral bodies. Phlegmon in the spine can be a diffuse enhancement, or localized abscess, (peripheral enhancement) in the epidural, subligamentous or paraspinous spaces. Under MRI examination, phlegmon will show dark with T1, and high signal (bright) with T2.

Peritonsillar abscess (PTA), also known as a quinsy, is pus due to an infection behind the tonsil. Symptoms include fever, throat pain, trouble opening the mouth, and a change to the voice. Pain is usually worse on one side. Complications may include blockage of the airway or aspiration pneumonitis.

They are typically due to infection by a number of types of bacteria. Often it follows streptococcal pharyngitis. They do not typically occur in those who have had a tonsillectomy. Diagnosis is usually based on the symptoms. Medical imaging may be done to rule out complications.

Treatment is by removing the pus, antibiotics, sufficient fluids, and pain medication. Steroids may also be useful. Admission to hospital is generally not needed. In the United States about 3 per 10,000 people per year are affected. Young adults are most commonly affected.

Secondary peritonitis and intra-abdominal abscesses including splenic and hepatic abscesses generally occur because of the entry of enteric micro-organisms into the peritoneal cavity through a defect in the wall of the intestine or other viscus as a result of obstruction, infarction or direct trauma. Perforated appendicitis, diverticulitis, inflammatory bowel disease with perforation and gastrointestinal surgery are often associated with polymicrobial infections caused by aerobic and anaerobic bacteria, where the number of isolates can average 12 (two-thirds are generally anaerobes). The most common aerobic and facultative bacteria are "Escherichia coli", "Streptococcus" spp. (including Enterococcus spp.), and the most frequently isolated anaerobic bacteria are the "B. fragilis" group, "Peptostreptococcus" spp., and "Clostridium" spp.

Abdominal infections are characteristically biphasic: an initial stages of generalized peritonitis associated with "Escherichia coli" sepsis, and a later stages, in which intra abdominal abscesses harboring anaerobic bacteria ( including "B. fragilis" group ) emerge.

The clinical manifestations of secondary peritonitis are a reflection of the underlying disease process. Fever, diffuse abdominal pain, nausea and vomiting are common. Physical examination generally show signs of peritoneal inflammation, isuch as rebound tenderness, abdominal wall rigidity and decrease in bowel sounds. These early findings may be followed by signs and symptoms of shock.

Biliary tract infection is usually caused by "E. coli, Klebsiella" and "Enterococcus" spp. Anaerobes (mostly "B. fragilis" group, and rarely "C. perfringens") can be recovered in complicated infections associated with carcinoma, recurrent infection, obstruction, bile tract surgery or manipulation.

Laboratory studies show elevated blood leukocyte count and predominance of polymorphonuclear forms. Radiographs studies may show free air in the peritoneal cavity, evidence of ileus or obstruction and obliteration of the psoas shadow. Diagnostic ultrasound, gallium and CT scanning may detect appendiceal or other intra-abdominal abscesses. Polymicrobial postoperative wound infections can occur.

Treatment of mixed aerobic and anaerobic abdominal infections requires the utilization of antimicrobials effective against both components of the infection as well as surgical correction and drainage of pus. Single and easily accessible abscesses can be drained percutaneously.

A nasal septal abscess is frequently a result of a secondary bacterial infection of a nasal septal hematoma. Individuals with this condition may also have fever, general malaise and nasal pain, including tenderness over the dorsum of the nose. A bilateral persistent nasal obstruction may also be present.

Anaerobes can be isolated from most types of upper respiratory tract and head and neck and infection and are especially common in chronic ones. These include tonsillar, peritonsillar and retropharyngeal abscesses, chronic otitis media, sinusitis and mastoiditis, eye ocular) infections, all deep neck space infections, parotitis, sialadenitis, thyroiditis, odontogenic infections, and postsurgical and nonsurgical head and neck wounds and abscesses., The predominant organisms are of oropharyngeal flora origin and include AGNB, "Fusobacterium" and Peptostreptococcus spp.

Anaerobes involve almost all dental infections. These include dental abscesses, endodontal pulpitis and periodontal (gingivitis and periodontitis) infections, and perimandibular space infection. Pulpitis can lead to abscess formation and eventually spread to the mandible and other neck spaces. In addition to strict anaerobic bacteria, microaerophilic streptococci and "Streptococcus salivarius" can also be present.

"Fusobacterium" spp. and anaerobic spirochetes are often the cause of acute necrotizing ulcerative gingivitis (or Vincent's angina) which is a distinct form of ulcerative gingivitis.

Deep neck infections that develop as a consequence of oral, dental and pharyngeal infections are generally polymicrobial in nature. These include extension of retropharyngeal cellulitis or abscess, mediastinitis following esophagus perforation, and dental or periodontal abscess.

Potential complications of a nasal septal abscess include cavernous sinus thrombophlebitis, septal perforation, or saddle deformity due to cartilage necrosis.

Some common symptoms and signs of mastoiditis include pain, tenderness, and swelling in the mastoid region. There may be ear pain (otalgia), and the ear or mastoid region may be red (erythematous). Fever or headaches may also be present. Infants usually show nonspecific symptoms, including anorexia, diarrhea, or irritability. Drainage from the ear occurs in more serious cases, often manifest as brown discharge on the pillowcase upon waking.