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- 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).
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).
- 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)
- 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.
No specific genetic predisposition has been described.
- Aspiration risk factors
- Alcohol intoxication
- Use of CNS depressant drugs (i.e., opiates)
- General anesthesia with surgery
- Dysphagia from muscular dysfunction either local or systemic
- Nasogastric tube and severe gastroesophageal reflux disease (GERD)
- Diabetes, altered mental status, coma
- Airway obstruction (3)
- External compression from lymph nodes
- Endobronchial foreign bodies
- Underlying abnormal parenchyma (bullous emphysema, bronchiectasis)
- Congenital malformation (i.e., bronchoesophageal fistula)
- Chronic steroid use
- Cystic fibrosis
- 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
- 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).