Lung Abscess

Lung Abscess is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Pulmonary abscess or lung abscess is a microbial infection of the lung that results in necrosis and destruction of the normal pulmonary parenchyma resulting in cavitation with or without central necrosis surrounded by thick wall (1).
  • Usually >2 cm in diameter (1,2)
  • Cavitations are filled with purulent material.
  • Necrotizing pneumonia and lung gangrene, which are on the same clinical spectrum, have multiple areas affected parenchyma.
  • If infected tissue involves visceral pleura, it will develop pyopneumothorax or pleural empyema (3).

Epidemiology

Incidence
  • Constitute an uncommon infection due to access to antibiotics and advances in oral and dental hygiene; exact incidence is unknown.
  • Mortality ranges from 2% to 38.2% (1,3) but can go as high as 75% if not recognized and treated in timely manner (2,3).
  • Middle-aged men have more predisposition.

Etiology and Pathophysiology

  • Commonly presents secondary to aspiration from oral bacteria from the gingival crevice, leading to inflammation cascade and eventual liquefactive necrosis of tissue
  • Less commonly, septic emboli from endocarditis can seed and predispose lung abscesses (2).
  • Classification
    • By etiology: primary (i.e., aspiration of secretions, necrotizing pneumonia) and secondary (i.e., bronchial obstruction, hematogenic dissemination) (3)
    • By time of development in acute (<6 weeks) versus chronic (>6 weeks) (3)
    • By routes of spreading: bronchogenic (i.e., aspiration, bronchial obstruction by tumor or foreign body) and hematogenic (i.e., endocarditis, septic emboli)
  • Microbiology
    • Preantibiotic era abscesses were caused by one type of bacteria, whereas more recently is cause by polymicrobial flora 90% of cases (3).
    • Immunocompetent hosts: anaerobic bacteria (i.e., Bacteroides fragilis, Fusobacterium capsulatum and Fusobacterium necrophorum, Peptostreptococcus, and microaerophilic streptococci) and aerobic bacteria (i.e., Staphylococcus aureus, including methicillin-resistant S. aureus [MRSA]; Streptococcus pyogenes and Streptococcus pneumoniae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Haemophilus influenzae type B, Acinetobacter spp., Escherichia coli, and Legionella)
    • Immunocompromised patients: gram-negative rods in addition to those mentioned above. Consider atypical organisms like fungi, Nocardia, Rhodococcus, Mycobacterium tuberculosis, and Actinomyces.
    • Rarely, amoebic liver abscesses can rupture through the diaphragm and cause lung abscess; consider if there is history of prolonged stay in an endemic region.

Genetics
No specific genetic predisposition has been described.

Risk Factors

  • Aspiration risk factors
    • Alcohol intoxication
    • Use of CNS depressant drugs (i.e., opiates)
    • Seizures
    • General anesthesia with surgery
    • Dysphagia from muscular dysfunction either local or systemic
    • Nasogastric tube and severe gastroesophageal reflux disease (GERD)
    • Gingivitis
    • Diabetes, altered mental status, coma
  • Airway obstruction (3)
    • Neoplasia
    • External compression from lymph nodes
    • Endobronchial foreign bodies
    • Underlying abnormal parenchyma (bullous emphysema, bronchiectasis)
    • Congenital malformation (i.e., bronchoesophageal fistula)
  • Immunosuppression
    • Neutropenia
    • Chemotherapy
    • HIV/AIDS
    • Chronic steroid use
    • Cystic fibrosis

General Prevention

  • Treatment of predisposing conditions
  • Aspiration precautions
  • Treatment of periodontal diseases and improving oral hygiene
  • Optimization of underlying comorbidities
  • Pulmonary physical therapy
  • Alcohol cessation counseling
  • Identifying underlying predispositions and correcting them
Pediatric Considerations
  • Lung abscess in children are rare and represents 0.7/100,000 admissions per year (1).
  • Pediatric population has toxic presentation that ranges from only loss of appetite to fever with altered mental status.
  • Lung abscesses after resolution have less morbidity when compared to adult presentations (1).
  • Commonly occurs in children with underlying conditions such as immunodeficiency syndromes, immunosuppression states, neurologic conditions which can predispose to aspiration (1)
  • S. aureus is the most common isolated etiologic pathogen in children (3).

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