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A lung abscess is a collection of pus within the lung parenchyma. While aspiration of oropharyngeal secretions is the most common cause, lung abscesses can also occur secondary to bronchial obstruction (e.g., malignancy, foreign body aspiration), hematogenous spread (e.g., infectious endocarditis, IV drug use), contiguous spread (e.g., liver abscess), and as a complication of necrotizing pneumonia. The most common causative pathogens are anaerobic bacteria, although aerobic bacteria and, in rare cases, fungi and parasites can also cause lung abscesses. Typical symptoms of a pyogenic lung abscess include fever and cough with production of foul-smelling sputum; they may take weeks or months to develop and may initially be attributed to pneumonia or pulmonary tuberculosis. Lung abscesses typically appear as spherical intraparenchymal cavitary lesions with an air-fluid level on chest imaging. Chest CT is useful for detecting smaller abscesses as well as differentiating abscesses from other cavitary pulmonary lesions. should be started immediately after obtaining relevant cultures and continued for several weeks. Occasionally, percutaneous or bronchoscopic drainage or surgical resection is required. The underlying cause should be evaluated for and treated in all patients.
- Lung abscess: a localized collection of pus and necrotic tissue within lung parenchyma caused by microbial infection
- Primary lung abscess: abscess in normal lung parenchyma, typically due to aspiration (∼ 80%)
- Secondary lung abscess: abscess in a patient with immunocompromise or preexisting disease (e.g., lung neoplasm), or due to hematogenous spread (e.g., septic emboli, IV drug use)
Causative pathogens 
Bacterial (pyogenic lung abscess)
- Most commonly caused by anaerobic bacteria that colonize the oral cavity (e.g., Peptostreptococcus spp., Prevotella spp., Bacteroides spp., Fusobacterium spp.)
- Less commonly caused by aerobic bacteria, such as:
- Parasitic: e.g., Entamoeba histolytica and Paragonimus westermani
- Fungal: e.g., Aspergillus spp., Cryptococcus spp., Coccidioides spp., and Histoplasma spp.
Risk factors for lung abscess 
, such as:
- Impaired consciousness
- Impaired swallow in neurological disorders and vocal cord paralysis
- Increased oropharyngeal bacterial growth (e.g., periodontal disease, dental abscesses, tonsillitis)
- Bronchial obstruction (e.g., lung cancer, foreign body aspiration, bronchial stenosis)
- Immunocompromised state
- Pneumonia, bronchiectasis
- Impaired respiratory mucus clearance (e.g., cystic fibrosis)
- Aspiration (most common etiology) of food or oropharyngeal secretions → pneumonitis and/or obstruction of the smaller airways → localized suppurative inflammation and necrosis → lung abscess formation (∼ after 1–2 weeks) 
- Other mechanisms by which lung abscesses can develop include: 
Typically indolent; symptoms can evolve over weeks to months, but may also be acute in onset.
- Acute: symptoms present for < 4–6 weeks
- Chronic: symptoms present for > 6 weeks
- Cough with production of foul-smelling purulent sputum
- Night sweats
- Anorexia, weight loss, fatigue
- Pleuritic chest pain
- Digital clubbing in chronic abscess
- Dullness to percussion over the affected area
- lung abscess may be present over the
General principles 
- All patients should undergo chest imaging, either CT (gold standard) or chest x-ray.
- Laboratory findings are typically nonspecific, showing signs of infection.
- Cultures of blood, sputum (or bronchoalveolar lavage), and any pleural fluid should be ordered to determine the causative pathogen.
- Further diagnostics (e.g., PCR testing, bronchoscopic-guided biopsy for suspected underlying neoplasm) may be required if there is an inadequate response to antibiotic therapy or for suspected secondary lung abscess.
- Chest x-ray: typically the initial investigation in any suspected lung pathology
- CT chest with IV contrast: to confirm the diagnosis and rule out 
Common findings on x-ray and CT
- Spherical intraparenchymal cavity with thick irregular walls
- Air-fluid level within the cavity that is dependent on body position
- Additional findings on CT
Location of abscess
- Due to aspiration: typically unilateral 
- Due to hematogenous dissemination: typically bilateral and multiple 
Laboratory studies 
- Blood culture
- Gram stain and culture
Additional testing (as needed)
HIV screening: Consider in the following situations. 
- Atypical pathogens are cultured
- No obvious identified
- Gram stain and culture of aspirate of abscess
Do not wait for culture results to start antibiotics. Start empirical treatment immediately after obtaining samples for culture, and tailor therapy as needed once culture results are available.
Diagnostics for the underlying cause
- Differential diagnoses of cavitary lung lesions, such as:
- See also “Differential diagnosis of pulmonary nodules.”
As lung abscesses due to aspiration appear in characteristic locations, imaging can help to differentiate them from other cavitary lesions. For example, tuberculosis more commonly affects the lung apices or apical segments of the lower lobes; embolic pulmonary infarcts typically appear as multiple, diffuse lesions. 
The differential diagnoses listed here are not exhaustive.
- Admit the patient and start immediate empiric antibiotic therapy (after obtaining samples for culture).
- Consider the following consults as appropriate:
- Identify and treat the underlying cause.
Antimicrobial therapy 
Suspected bacterial infection
Bacterial infection is the most common cause of lung abscess and empiric antibiotic therapy should be initiated in all patients with typical clinical features (e.g., fever, purulent sputum) and a cavitary lesion on imaging.
- Broad-spectrum antibiotics with anaerobic coverage are recommended; (e.g., ampicillin-sulbactam, carbapenems, or clindamycin).
- Ensure antibiotic coverage of gram-positive cocci in lung abscesses that are likely due to IV drug use. 
- Parenteral antibiotic therapy is preferred for seriously ill patients.
- Tailor antibiotic therapy as needed based on culture results and clinical response.
- Antibiotics are typically continued for 3–6 weeks or until clinical and radiological improvement is seen 
|Empiric antibiotic therapy for bacterial lung abscess |
|No risk factors for MRSA infection|
|Suspected MRSA infection|
Lung abscesses due to aspiration are typically caused by anaerobic bacteria. Lung abscesses due to hematogenous spread from IV drug use are typically caused by Staphylococcus aureus and streptococci. 
Parasitic or fungal infection 
Suspect parasitic or fungal infection in patients with atypical clinical features (e.g., nonpurulent sputum), an inadequate response to empiric antibiotic therapy, and risk factors (e.g., immunocompromise)
- Management of immunocompromised status, which includes: 
- Treatment depends on the underlying organism and whether disseminated disease is present.
Interventional therapy 
- Options 
Management of the underlying cause
- Extension or rupture into the pleural cavity, causing:
- Recurrence of abscess
- Development of chronic reactive changes: e.g., bronchiectasis or pneumatoceles
- Massive hemoptysis
We list the most important complications. The selection is not exhaustive.
Acute management checklist for lung abscess
- Confirm diagnosis on imaging.
- Send cultures of sputum (or bronchoalveolar lavage), blood, and any pleural fluid.
- Start .
- Consider if there are any indications for invasive treatment (e.g., large abscess, underlying malignancy, or significant hemoptysis) and refer to appropriate services as needed.
- Identify and treat the underlying cause.