Practice Essentials
A lung abscess is a subacute infection that destroys lung parenchyma. Furthermore, chest radiographs reveal one or more cavities, often with an air-fluid level. Because the development of a cavity requires some amount of prior tissue damage and necrosis, it may be presumed that lung abscesses usually begin as a localized pneumonia.
Before the availability of antibiotics, a typical abscess arose from complications after oral surgical procedures (ie, tonsillectomy), resulting in aspiration of infected material into the lungs. In the absence of satisfactory antibiotic treatment, this event usually led to a lung abscess or to a necrotizing pneumonia with or without pleural empyema.
In the preantibiotic era, the clinical course of a patient with a lung abscess would gradually worsen. At one time, mortality was in excess of 50%, and many patients were left with significant residual symptomatic disease. Most patients underwent surgery during the latter stages of the disease, and the results were discouraging.
The availability of effective antibiotic therapy for primary lung abscess has drastically modified the natural history of the disease and diminished the role of surgery. [1] In current practice, operative indications are less frequent, and these procedures are undertaken electively for chronic illnesses only after medical therapy has been unsuccessful.
In addition to antibiotics, pulmonary care has advanced and now includes postural drainage. Currently, bronchoscopy is occasionally employed as an adjunct to expedite drainage and to identify underlying occult lesions (eg, foreign bodies and malignancies).
The increasing use of corticosteroids, immunosuppressive drugs, and chemotherapeutic agents has changed the natural milieu of the oropharyngeal cavity and contributed to the mounting frequency of opportunistic lung abscesses.
Lung abscesses are commonly classified on the basis of their duration, as follows:
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Acute - < 6 weeks
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Chronic - >6 weeks
They may also be classified as follows:
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Bronchogenic (due to inhalation or aspiration)
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Hematologic (spread via the bloodstream from other infected sites)
For patient education resources, see the Infections Center, Lung and Airway Center, Pneumonia Center, and Procedures Center, as well as Bacterial Pneumonia, Abscess, Antibiotics, and Bronchoscopy.
Pathophysiology
Aspiration of infectious material is the most frequent pathogenetic mechanism in the development of pyogenic lung abscess. Aspiration due to dysphagia (eg, achalasia) or to compromised consciousness (eg, alcoholism, seizure, cerebrovascular accident, or head trauma) appears to be a predisposing factor. Poor oral hygiene, dental infections, and gingival disease are also common in these patients.
Although lung abscesses can occur in edentulous patients, an occult carcinoma should be considered. Edentulous patients very seldom, if ever, develop a putrefied abscess, because they lack periodontal flora. In many studies, dental caries and poor oral mouth hygiene have been major contributing factors for lung abscesses. [2]
Patients with alcoholism and those with chronic illnesses frequently have oropharyngeal colonization with gram-negative bacteria, especially when they undergo prolonged endotracheal intubation and receive agents that neutralize gastric acidity. A pyogenic lung abscess can also develop from aspiration of infectious material from the oropharynx into the lung when the cough reflex is suppressed in a patient with gingivodental disease.
Abscesses generally develop in the right lung and involve the posterior segment of the right upper lobe, the superior segment of the lower lobe, or both. This is due to gravitation of the infectious material from the oropharynx into these dependent areas. Initially, the aspirated material settles in the distal bronchial system and develops into a localized pneumonitis. Within 24-48 hours, a large area of inflammation results, consisting of exudate, blood, and necrotic lung tissue. The abscess frequently connects with a bronchus and partially empties.
After pyogenic pneumonitis develops in response to the aspirated infected material, liquefactive necrosis can occur secondary to bacterial proliferation and an inflammatory reaction to produce an acute abscess. As the liquefied necrotic material empties through the draining bronchus, a necrotic cavity containing an air-fluid level is created. The infection may extend into the pleural space and produce an empyema without rupture of the abscess cavity. The infectious process can also extend to the hilar and mediastinal lymph nodes, and these too may become purulent. (See the images below.)
Histologic evaluation of lung abscess shows dense inflammatory reaction (low power).
Etiology
Lung abscesses have numerous infectious causes. Anaerobic bacteria continue to be accountable for most cases. These bacteria predominate in the upper respiratory tract and are heavily concentrated in areas of oral-gingival disease. Other bacteria involved in lung abscesses are gram-positive and gram-negative organisms.
More specifically, gram-negative organisms that have been associated with lung abscess include the following:
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Bacteroides species
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Fusobacterium species
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Proteus species
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Aerobacter species
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Escherichia coli
Gram-positive organisms that have been associated with lung abscess include the following:
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Peptostreptococcus species
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Microaerophilic Streptococcus
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Clostridium species
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Staphylococcus species
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Actinomyces species
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Nocardia species [3]
Opportunistic organisms associated with lung abscess include the following:
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Candida species
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Legionella species
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Mycobacterium species
However, lung cavities may not always be due to an underlying infection. Some evidence suggests that individuals with cyanotic heart disorders may also be more prone to lung abscess formation. The continuous hypoperfusion of the pulmonary tissues may predispose the individuals to chronic pulmonary infections. [4]
Factors contributing to lung disease include the following:
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Oral cavity disease - Periodontal disease, gingivitis
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Sinus infections
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Altered consciousness - Alcoholism, coma, drug abuse, anesthesia, seizures
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Immunocompromised host - Steroid therapy, chemotherapy, malnutrition, multiple trauma
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Esophageal disease - Achalasia, reflux disease, depressed cough and gag reflex, esophageal obstruction
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Bronchial obstruction - Tumor, foreign body, stricture, enlarged lymph nodes
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Generalized sepsis
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Persistent vomiting
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Mechanical ventilation, tracheostomy
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Intravenous (IV) drug use
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Infected central venous catheters
Prognosis
The prognosis of patients with lung abscesses depends on the underlying or predisposing pathologic event and the speed with which appropriate therapy is established. Negative prognostic factors include the following:
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Large (>6 cm) cavity
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Necrotizing pneumonia
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Multiple abscesses
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Immunocompromise
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Age extremes
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Associated bronchial obstruction
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Aerobic bacterial pneumonia
The mortality associated with an anaerobic lung abscess is lower than 15%, though it is slightly higher in patients with necrotizing anaerobic pneumonia and pneumonia caused by gram-negative bacteria. The prognosis associated with amebic lung abscess is good when treatment is prompt. Overall, lung abscess can have a better prognosis and shorter length of hospital admission if the diagnosis is made promptly and a consensus on antibiotics is available. [5]
Most cases of empyema have an infectious cause and add high morbidity, as well as increase hospital costs. In patients who have empyema with a lung abscess, morbidity is even higher; hence, more aggressive early treatment is recommended. [6]
Over the years, numerous prognostic factors have been identified in patients with lung abscess. The two main factors are advanced age and the presence of comorbidity. The rate of reduction of the abscess is also felt to be predictive of recurrence. This again emphasizes the importance of follow-up with an imaging study, such as computed tomography (CT). [7]
In a study of 91 patients who underwent major thoracic surgery for infectious lung abscess at six centers for general thoracic surgery in Europe and and the United States, Schweigert et al found that the following were significant predictors of fatal outcome [8] :
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Pulmonary sepsis
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Septic complications (air leak, pleural empyema)
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Septic organ failure (respiratory, acute renal failure)
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Preexisting comorbidity (Charlson index of comorbidity ≥3)
The extent of surgical resection was not found to have a significant influence on the risk of a fatal outcome. [8]
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Histologic evaluation of lung abscess shows dense inflammatory reaction (low power).
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Thick-walled lung abscess.
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Lateral chest radiograph shows air-fluid level characteristic of lung abscess.
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Chest radiograph reveals lung abscess occurring as complication of necrotizing pneumonia.
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CT reveals lung abscess with air-fluid level occurring as complication of necrotizing pneumonia.
