An Overview of Lung Abscess

A lung abscess, also called a pulmonary abscess, is a pus-filled cavity in the lungs caused by an infection.

It's usually caused by a bacterial infection, and sometimes by fungi or parasites. A lung abscess may be diagnosed with imaging studies of the chest. They usually resolve with antibiotics, but in some cases, drainage or surgery is needed.

Signs, Symptoms, and Complications

The symptoms of a lung abscess may worsen rapidly, or they can come on slowly and insidiously.

Abscesses are described as:

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

Early signs and symptoms may include:

• Fever and chills
• Night sweats
• Persistent cough: At first the cough is usually dry, but it may become productive (coughing up phlegm), especially if an abscess ruptures into the bronchi.

Later signs and symptoms may include:

• Pain with deep breathing
• Hemoptysis (coughing up blood)
• Shortness of breath
• Foul-smelling and/or foul-tasting sputum
• Unintentional weight loss
• Fatigue
• Clubbing, an upside-down spoon-like appearance of the fingernails

Complications

If a lung abscess persists or if the diagnosis is delayed, complications may occur.

Complications of an untreated lung abscess can include:

• Empyema: An abscess may rupture into the pleural cavity, the space between the membranes that line the lungs.
• 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 of the body, especially the brain, resulting in a brain abscess or a stroke.
• Secondary amyloidosis

Causes and Risk Factors

Lung abscesses may be primary or secondary. A primary lung abscess develops in a region of pneumonia or another lung disease. A secondary lung abscess occurs when an infection from another region of the body spreads to the lungs.

Abscesses can be single or multiple. Multiple abscesses tend to occur with pneumonia or due to sepsis.

Primary Lung Abscess Causes and Risk Factors

Some conditions that directly affect the lungs may predispose to a lung abscess.

• Pneumonia: Any type of pneumonia, including aspiration pneumonia, may lead to a lung abscess, especially if diagnosis and treatment are delayed.
• Tumors: Cancer contributes to the formation of a lung abscess in roughly 10 percent or 15 percent of people. Obstruction of the airways due to a tumor often leads to post-obstructive pneumonia, which leads to an abscess. Squamous cell carcinoma of the lungs is the most common form of lung cancer to cause a lung abscess, but other cancers, such as lymphomas, can cause it as well.
• 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 an infection from another area of the body spreads to the lungs. This can occur by inhalation (aspiration), through the bloodstream, or from outside the body (such as with penetrating trauma).

Causes of secondary lung abscess include:

• 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 (infectious endocarditis), an infected central catheter, or IV drug abuse.
• Penetration: Infection may penetrate to the lungs from nearby regions such as the esophagus, 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: Alcohol and other drug use, 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

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 methicillin-resistant Staphylococcus aureus (MRSA)
• 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.

For example:

• 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 anaerobic 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 (developed 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. Klebsiella is associated with underlying diabetes.

Diagnosis

A lung abscess may be suspected based on symptoms and risk factors, as well as physical findings.

On physical exam, a fever is common. Your healthcare professional may hear bronchial breath sounds and the area overlying an abscess may sound dull when the chest is tapped. This is described as dullness to percussion.

Imaging

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

Some imaging changes associated with a lung abcess:

• As an abscess progresses, the abscess cavity may be seen more clearly on imaging tests and may appear as a thick-walled cavity with an air-fluid level (often surrounded by evidence of pneumonia).
• At later stages, the abscess may become less clear on imaging tests as the area is replaced by scar tissue.
• The most common locations of abscesses that occur due to aspiration are the right middle lobe or the upper portions of the lower lobes of either lung.

Bacterial Analysis/Culture

A sputum sample (sample of coughed up phlegm) is sometimes taken but tends to be inaccurate.

Blood cultures are often negative when anaerobes are the predominant type of bacteria present because these organisms can take longer to grow in the blood.

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 appears as a round cavity inside the lungs, whereas an empyema is located in the pleural space (outside lungs or between lungs and chest wall).

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

Some of these include:

• Tuberculous cavity
• Pulmonary infarct, which is an area of cell death in the lungs due to lack of blood flow
• Cavitary lesions due to lung cancer
• Fungal infections
• Granulomas due to rheumatoid nodules in the lungs
• Necrotizing pneumonia, which is usually marked by multiple areas of cavitation

Treatment

Antibiotics alone are often sufficient in treating a lung abscess and are effective roughly 80 percent of the time. Drainage or surgery is seldom needed for the treatment of lung abscesses.

Drainage is the preferred method of treatment for abscesses in many other regions of the body,

Antibiotics and Lung Physiotherapy

A combination of broad-spectrum antibiotics is most often used to treat the variety of bacteria present. 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—possibly up to 6 months.

If the abscess doesn't improve with antibiotics, other treatments may be needed.

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

Percutaneous or Endoscopic Drainage

If a lung abscess doesn't respond to antibiotic therapy (less than 10 percent of cases), drainage may be needed. This is usually considered if no improvement is noted after 10 to 14 days of antibiotics.

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 considered 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 very rare cases, surgery may be required. The most common procedures are a lumpectomy or segmentectomy in which the abscesses and some surrounding tissue is removed. This 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 not successfully treated with antibiotics or drainage
• When an underlying cancer is suspected

Prognosis

With timely antibiotic treatment, the prognosis of a lung abscess often depends on the underlying cause, and many lung abscesses resolve without any long-term problems.

Prompt recognition and treatment of a lung abscess are important for reducing the risk of complications.

As with many conditions, prevention is key. Good dental hygiene, prompt medical attention for suspected pneumonia, careful management of blood sugars if you have diabetes, and airway management can help reduce your risk.