Lung Abscess

Causes

aspiration of oropharyngeal contents
- in patients predisposed to lose consciousness
  - alcoholics, epileptics, comatosed
  - cavitations may occur ; air-fluid levels on CXR
  - due to anaerobes (eg, Bacteroides, Fusobacterium, Peptostreptococcus) or S aureus
bronchial obstruction (eg, cancer)
complication of bacterial pneumonia (necrotizing)
- nosocomial ; caused by S.aureus, E. coli, Klebsiella, Pseudomonas aeruginosa
- secondary to TB / bronchiectasis
hematogenous spread of infection
- in patients with septicemia or infectious endocarditis (septic emboli)
- often multiple and monomicrobial
- most common causative agents being Staph and Strep

Lysosomal enzymes serve to digest the offending pathogens and tissue debris, as well as to chemotactically summon additional neutrophils or macrophages to the area
Occasionally, however, the enzymes will also damage the surrounding parenchyma, setting the stage for abscess formation
Suppurative destruction : necrosis secondary to the release of lysosomal enzymes by neutrophils and macrophages

Lung abscess 2° to aspiration is most often found in right lung. Location depends on patient’s position during aspiration:

Upright = basal segments of right lower lobe
Supine = posterior segments of right upper lobe or superior segment of right lower lobe