Pneumonia Acute inflammation of lung parenchyma Inflammatory infiltrate in alveoli ( = consolidation)
CLASSIFICATION: Aetiology. Morpological class. - Bronchopneumonia vs. lobar pneumonia. Community acquired vs hospital acquired (nosocomial) infection. The patient's immune status.
AETIOLOGY Bacteria, viruses, fungi, mycoplasma, chlamydia. Microbiological identification of organism often not possible.
Previously healthy individual: S. pneumoniae Pre-existing viral infection Staph. aureus or S. pneumoniae Chronic bronchitis Haemophilus influenzae or S. pneumoniae AIDS Pneumocystis carinii, cytomegalovirus, TB
Morphological classification - Bronchopneumonia - Lobar pneumonia
Bronchopneumonia: Infants + young children and the elderly. Usually secondary to other conditions associated with local and general defence mechanisms: - viral infections (influenza, measles) - aspiration of food or vomitus - obstruction of a bronchus (foreign body or neoplasm) - inhalation of irritant gases - major surgery - chronic debilitating diseases, malnutrition
Lobar pneumonia: S. pneumoniae. Previously healthy individuals. Abrupt onset. Unilateral stabbing chest pain on inspiration (due to fibrinous pleurisy).
Pathology of lobar pneumonia: 4 phases: Congestion Lasts < 24 hours: Alveoli filled with oedema fluid and bacteria.
Red hepatization Firm, 'meaty' and airless appearance of lung. Alveolar capillary dilatation. Strands of fibrin extending from one alveolus to another via inter-alveolar pores of Kohn. Also neutrophils in alveoli. Pleura: Fibrinous exudate.
Grey hepatization Less hyperaemia. Macrophages, neutrophils + fibrin
Resolution - Lysis and removal of fibrin via sputum + lymphatics. - Begins after 8-9 days (without antibiotics). - Sudden improvement of patient's condition.
Complications of lobar pneumonia 1. Abscess formation 2. Empyema 3. Failure of resolution intra-alveolar scarring ('carnification') permanent loss of ventilatory function of affected parts of lung. 4. Bacteraemia: - Infective endocarditis - Cerebral abscess / meningitis - Septic arthritis
Klebsiella pneumoniae Common inhabitant of oral cavity (poor oral hygiene). Lobar pneumonia in the elderly, diabetics, alcoholics (aspiration of saliva).
Community acquired vs. nosocomial infection Nosocomial infection: - Often patients in ICU - Local resistance to infection in lungs - Intubation of respiratory tract - Altered normal flora due to antibiotics - E.coli, Klebsiella, Proteus, Pseudomonas, Staph. aureus.
Immune status Infection by usually non-pathogenic organisms ('opportunistic infection') - Pneumocystis carinii - Other fungi - Cytomegalovirus (CMV)
Fig. A viral pneumonia with interstitial lymphocytic infiltrates. Note that there is no alveolar exudate. Thus, the patient with this type of pneumonia will probably not have a productive cough.
The most common causes for viral pneumonia are: Influenza Parainfluenza Adenovirus Respiratory syncytial virus (RSV) - appears mostly in children Cytomegalovirus - in immunocompromised hosts.
Fig. RSV accounts for many cases of pneumonia in children under 2 years, and can be a cause for death in infants 1 to 6 months of age or older.
Lung abscess DEFINITION: Localised area of suppuration and tissue necrosis.
Fig. Chest X-ray. Abscess. Note air-fluid level
Aetiopathogenesis Aspiration of infected oropharyngeal contents / vomitus. NB: Poor oral hygiene and sepsis. Risk of aspiration: - Loss of consciousness (alcoholic stupor, anaesthesia, epilepsy). - Oesophageal pathology (carcinoma, congenital atresia / fistula).
Obstruction of bronchus - carcinoma, foreign body. Complication of pneumonia - virulent organisms esp. Klebsiella, Staph. Bronchiectasis. Septic embolism (infective endocarditis on right-sided heart valves) or septisaemia. Penetrating trauma e.g. stab wound. Direct spread of sepsis from other organs (e.g. amoebic liver abscess).
Complications Rupture into pleural space empyema or broncho-pleural fistula ( pyopneumothorax). Rupture into pericardium pericarditis. Septisaemia sepsis in other organs e.g. osteomyelitis, brain abscess. Erosion of blood vessels haemoptysis. Organisation fibrosis.