Pneumonia

What's in the alveoli?

• Consolidation = Many bacteria + scattered polymorphs + oedema fluid.
  
  
• Red hepatisation = Packed with polymorphs + red cells + fibrin + fibrinous pleurisy.
  
  
• Grey hepatisation = Red cells lyse + fibrinous exudate persists.
  
  
• Resolution = Exudate resorbed/digested/expectorated + intact structure + pleura resolves or organises with adhesions.

This happens in both lobar and broncho pneumonia, but is more 'dramatic' in bronchopneumonia.

Pleural involvement is more common in lobar pneumonia, and complications are more common in lobar pneumonia.

Uncommon complications of pneumonia

1. Lung abscess (a localised suppurative area, characterised by necrosis).
2. Empyema.
3. Alveolar fibrosis in organisation.
4. Bacteraemia with metastatic abscesses --> endocarditis, meningitis, arthritis.
5. Pleural adhesions.
6. Bronchiectasis (caused by necrotising pneumonias, commonly due to anaerobes +/- aerobes and uncommonly due to S. aureus, Klebsiella, or S. pyogenes type 3 pneumococcus).