An Overview of Lung Abscess

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A lung abscess or pulmonary abscess is a pus-filled cavity in the lungs caused by infections with bacteria or sometimes fungi or parasites. They may be primary, developing in a region of pneumonia or other lung disease, or secondary, in which bacteria from another region of the body are aspirated into the lungs or spread to the lungs in another way. A lung abscess may be seen on chest X-ray, though the best test for diagnosis is a chest CT. The majority of the time they resolve with antibiotics alone, but in some cases drainage or surgery is needed.

Signs, Symptoms, and Complications

The symptoms of a lung abscess may begin rapidly, or come on slowly and insidiously. Abscesses are described as:

  • Acute: Less than 6 weeks in duration
  • Chronic: Greater than 6 weeks

Early signs and symptoms may include:

  • Fever and chills: A fever is often the first sign of a lung abscess, with at least 80% of people experiencing this symptom.
  • Night sweats: In contrast to "hot flashes," night sweats are often described as "drenching" and require a change of nightclothes. Sweats may also occur during the day.
  • Persistent cough: At first the cough is usually dry, but may become productive (coughing up phlegm), especially if an abscess ruptures into the bronchi.

Later signs and symptoms may include:

Complications

If a lung abscess persists or if the diagnosis is delayed, a number of complications may occur. These include:

  • Empyema: An abscess may rupture into the pleural cavity, the space between the membranes that line the lungs. When this occurs, the condition is often treated differently.
  • Bronchopleural fistula: A fistula (abnormal passageway) may develop between a bronchus and the pleural cavity.
  • Gangrene of the lungs
  • Hemorrhage (bleeding into the lungs)
  • Septic emboli: Pieces of the abscess may break off and travel to other regions, especially the brain, resulting in a brain abscess or meningitis.
  • Secondary amyloidosis

Causes and Risk Factors

Lung abscesses are broken down into two main categories when looking at potential causes:

  • Primary: A primary lung abscess stems from an extension of a condition involving the lung itself.
  • Secondary: Lung abscesses may occur secondarily as the result of a condition outside of the lungs spreading to the lungs.

These causes, in turn, have different underlying risk factors.

Most Common Cause

The most common cause of a lung abscess is aspiration of anaerobic bacteria (bacteria that live without oxygen) from the mouth.

Abscesses can be single or multiple, with multiple abscesses more commonly found with pneumonia or due to sepsis.

Primary Lung Abscess Causes and Risk Factors

A number of conditions that directly affect the lungs may predispose a person to developing a lung abscess.

  • Pneumonia: Any type of pneumonia, but especially aspiration pneumonia may lead to a lung abscess, especially if diagnosis and treatment are delayed.
  • Tumors: An underlying cancer contributes to the formation of a lung abscess in roughly 10% or 15% of people. In this case, obstruction of the airways due to a tumor often leads to pneumonia (post-obstructive pneumonia), which in turn leads to an abscess. Squamous cell carcinoma of the lungs is the most common form of lung cancer to result in a lung abscess, but other cancers, such as lymphomas, may also be the root cause.
  • Underlying lung disease: Lung conditions such as bronchiectasis, cystic fibrosis, lung contusions (bruises), and infected infarcts may lead to a lung abscess.
  • Immune deficiency: Congenital immunodeficiency syndromes, as well as those acquired (such as with HIV/AIDS or due to chemotherapy), may lead to a lung abscess.

Secondary Lung Abscess Causes

A secondary lung abscess may occur when bacteria present in other regions spread to the lungs by inhalation (aspiration), via the bloodstream, or from outside the body (such as with penetrating trauma).

  • Aspiration of infective material from the mouth and upper airways
  • Septic emboli: Infections may spread via the bloodstream to the lungs from an area of thrombophlebitis, an infected heart valve (bacterial endocarditis) on the right side of the heart (such as the tricuspid valve), an infected central catheter, or IV drug abuse.
  • Penetration: Infection may penetrate through to the lungs from nearby regions such as the esophagus (bronchoesophageal fistula), a mediastinal infection, or an abscess under the diaphragm (subphrenic abscess).

Risk Factors

Risk factors for a lung abscess include:

  • Decreased level of consciousness leading to aspiration: Alcoholism and other drug abuse, coma, stroke, general anesthesia, seizure disorders, mechanical ventilation
  • Decreased muscle control: Neuromuscular conditions that lead to dysphagia (difficulty swallowing), or an inability to cough.
  • Dental issues: Dental decay, poor dental hygiene, dental and periodontal infections (eg. gum disease)
  • Upper airway conditions: Sinus infections, oropharyngeal surgery
  • Immune suppression: Long term corticosteroid use, immunosuppressant medications, sepsis, advanced age, malnutrition
  • Other conditions: Diabetes (especially a risk factor for lung abscesses with Klebsiella, gastroesophageal reflux disease, bronchial obstruction, joint and muscle infections, sepsis

Alcohol abuse is the most common risk factor for lung abscess (but certainly not the only cause).

Pathogens (Bacteria and Other Organisms Present in the Abscess)

Lung abscesses most often contain a combination of both aerobic (bacteria that live in oxygen) and anaerobic bacteria, with an average of six or seven different species present. The type of bacteria present varies depending on the underlying cause, whether the infection begins in the community or the hospital setting, and geography.

Anaerobic bacteria are usually most predominant and can include:

  • Bacteroides
  • Fusobacterium
  • Peptostreptococcus magnus (now called Finegoldia magna)
  • Prevotella melaninogenica
  • Porphyromonas
  • Bacteroides fragilis
  • Clostridium perfringens
  • Veillonella (more common in children who have had surgery, and in people with cancer or immunodeficiency)

Aerobic bacteria are also commonly present, especially in people who are immunocompromised. These may include:

  • Klebsiella pneumoniae
  • Haemophilus influenzae
  • Pseudomonas aeruginosa
  • Legionella
  • Staphylococcus aureus, including MRSA (multiple abscesses may be present)
  • Streptoccous pneumoniae, Streptococcus pyogenes, Streptoccocus anginosus, or group B strep
  • Nocardia species
  • Actinomyces species
  • Burkholderia pseudomallei (SE Asia)
  • Mycobacterium species

Parasites

  • Entamoeba histolytica (hydatid cysts)
  • Paragogonimus westermani
  • Echinococcus

Fungi

  • Aspergillus
  • Blastomyces
  • Histoplasma
  • Cryptococcus
  • Coccidioides
  • Fusarium

Bacteria Associated with Underlying Causes

The types of bacteria found in an abscess are associated with the underlying cause and risk factors. Staph. aureus is a common culprit when multiple abscesses are seen, and is more commonly found in secondary abscesses, such as those associated with heart valve infections. Other common bacteria found in secondary lung abscesses include Streptococcus, Klebsiella, Pseudomonas, Haemophilus parainfluenzae, Acinetobacter, and Escherichia coli. Primary lung abscesses are often caused by gram-negative bacteria such as Bacteroides, Clostridium, and Fusobacterium.

Responsible Bacteria May Be Changing

In the past, anaerobes were the predominant bacteria present in community-acquired abscesses (people who developed abscesses outside of the hospital), with Streptococcus following as the second most common cause. This appears to be changing, and now Klebsiella is commonly found in community-acquired abscesses. The association of Klebsiella with underlying diabetes, and the recent increase in diabetes, may play a role.

Diagnosis

A lung abscess may be suspected based on symptoms and risk factors, as well as physical findings. On physical exam, a physician may hear bronchial breath sounds with the area overlying an abscess sounding dull when tapping on the chest (dullness to percussion). Fever is commonly present. Risk factors, such as dental decay and gum disease may also be noted.

Imaging

Early on, a chest X-ray may only show infiltrates (evidence of pneumonia) without an obvious abscess present. Chest computerized tomography (CT) is the most reliable test, although an ultrasound of the lungs may also be helpful in evaluating an abscess, especially in children. CT is also helpful in distinguishing between a lung abscess and empyema (which is important as the two conditions are treated in different ways).

As an abscess progresses, the abscess cavity may be seen more clearly on imaging, an may be seen as a thick-walled cavity with an air-fluid level (often surrounded by evidence of pneumonia). As the abscess progresses further, it may become less clear on imaging tests as the area is replaced by scar tissue.

In abscesses that are due to aspiration, the most common locations of an abscess are the right middle lobe or the upper portions of the lower lobes of either lung.

Bacterial Analysis/Culture

A sample may be taken to evaluate the type of bacteria present but is not always needed. A sputum sample (sample of coughed up phlegm) is sometimes taken, but tends to be inaccurate. More accurate samples may be obtained via an endobronchial ultrasound/aspiration during a bronchoscopy. Blood cultures are often negative when anaerobes are the predominant type of bacteria present.

Differential Diagnosis

An important first step in evaluating a lung abscess is to distinguish an abscess from an empyema, though an empyema may occur as a complication of an abscess. On imaging, a lung abscess often appears as a round cavity, whereas an empyema has more of a biconvex shape.

There are a number of conditions other than abscesses that may cause cavitation in the lungs. Some of these include:

  • Tuberculosis (tuberculous cavity)
  • Pulmonary infarct: Area of cell death in the lungs due to lack of blood flow as occurs with a heart attack (myocardial infarction) or stroke (cerebrovascular infarct)
  • Cancer (cavitary lesions due to lung cancer)
  • Fungal infections
  • Granulomas (with rheumatoid nodules in the lungs)
  • Necrotizing pneumonia (usually marked by multiple areas of cavitation)

Treatment

While drainage is the preferred method of treatment for abscesses in many regions of the body, drainage or surgery is seldom needed with lung abscesses. Antibiotics alone are often sufficient in treating a lung abscess, and are effective roughly 80% of the time.

Antibiotics and Lung Physiotherapy

A combination of broad-spectrum antibiotics is most often used to cover the variety of bacteria present. Depending on how ill a person is, antibiotics are often started intravenously, and continued for four weeks to six weeks or until evidence of the abscess is no longer seen on imaging studies.

With abscesses due to fungi, parasites, as well as infections with Mycobacterium, Actinomyces, or Nocardia, a longer duration of treatment may be needed, for example, up to 6 months.

Antibiotics alone lead to resolution of the abscess roughly 80% of the time, but if improvement isn't seen, other treatments may be needed.

Lung physiotherapy and postural drainage are frequently helpful as well, and often are combined with antibiotic treatment.

Percutaneous or Endoscopic Drainage

If a lung abscess doesn't respond to antibiotic therapy, drainage may still be needed. This is usually considered if no improvement is noted after 10 days to 14 days of antibiotics, and should be considered earlier rather than later in this case.

Drainage may either be done via a needle inserted through the chest wall into the abscess (percutaneous drainage) or via a bronchoscopy and endobronchial ultrasound (endobronchial drainage). Endobronchial drainage may be a better option for abscesses that are centrally located and away from the pleura when there is a risk of puncturing lung tissue, but percutaneous drainage is done more often.

Surgery

In rare cases (roughly 10% of the time), surgery may be required. The most common procedures are a lumpectomy or segmentectomy in which the abscesses and some surrounding tissue is removed, and can often be done with minimally invasive surgery (video-assisted thoracoscopic surgery, or VATS).

Indications for surgery may include:

  • Large abscesses (larger than 6 centimeters or roughly 3 inches in diameter).
  • Coughing up blood
  • Sepsis
  • Prolonged fever or elevated white blood cell count
  • Bronchopleural fistula formation
  • Empyema
  • Abscesses that are unsuccessfully treated with antibiotics or drainage
  • When an underlying cancer is suspected

Prognosis

Before antibiotics were available, the prognosis for lung abscesses was poor. Now, with timely antibiotic treatment, the prognosis often depends more on the underlying cause, and many lung abscesses resolve without any long term problems.

Lung abscesses are, in general, much less serious than in the past due to the widespread availability of broad-spectrum antibiotics.

A Word From Verywell

Prompt recognition and treatment of a lung abscess are important in order to reduce complications of the condition. As with many conditions, prevention is the best "cure." Good dental hygiene, prompt medical attention for suspected pneumonia, careful management of blood sugars in those who have diabetes, and airway management in people who are predisposed all play a role in reducing risk.

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Article Sources

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Additional Reading

  • Long, S. S., Prober, C. G., & Fischer, M. (2018). Principles and practice of pediatric infectious diseases. Philadelphia, PA: Elsevier.