Pathology of pneumonia Flashcards
Recall the components of the lower respiratory tract
- Larynx
- Trachea
- Primary bronchi
- Secondary bronchi
- Tertiary bronchi
- Bronchioles
- Terminal bronchioles
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
- Alveoli
Recall the histology of trachea, primary bronchi and lobar bronchus
- respiratory epithelium: pseudostratified columnar ciliated epithelium
- mucosa
- submucosal glands for lubrication
- hyaline cartilage
Describe normal lung macroscopy
- pink
- aerated
- mild anthracosis at apices
- just covering heart
Describe pulmonary infections broadly
- Respiratory tract infections are more frequent than infections of any other organ.
- Upper respiratory tract infections are primarily caused by viruses.
- Lower respiratory tract infections are common and are caused by bacterial, viral, mycoplasmal, and fungal infections.
Describe the three determinants of pneumonia pathogenesis
- virulence of organism
- host and factors affecting resistance
- factors affecting airway defences
List the two types of airway defences
- local defence mechanisms
- systemic resistance of the host
Describe local and systemic defence mechanisms
Local Defense Mechanisms
- Nasal clearance
- Tracheobronchial clearance (Muco-ciliary action)
- Alveolar clearance (Alveolar macrophages)
Systemic Resistance of Host
- Innate immunity
- Humoral immunity
Breakdown factors affecting resistance and airway defence
Factors affecting resistance in general
- Extremes of age
- Other conditions: chronic diseases, immunodeficiency (immunosuppressive treatment, leukopenia)
Factors affecting airway defenses (local defense)
- Altered cough reflex (anaesthesia, coma, drugs)
- Injury to mucociliary apparatus (cigarette smoking, immotile cilia syndrome)
- Interference of macrophage activity (alcohol, tobacco smoke)
- Accumulations of airway secretions (cystic fibrosis, bronchial obstruction)
Define pneumonia
- Inflammation of the lung parenchyma usually associated with consolidation.
- Wide variety of causes.
- Majority are either bacterial or viral.
Describe the features of bacterial pneumonia
- Respiratory tract exposed to 10,000 L of air per day.
- Bacteria 1-5 um can be deposited in the terminal airways or bronchi.
- Bacterial invasion evokes an acute inflammatory reaction.
- Consolidation.
Breakdown the classifications of pneumonia
Anatomic Distribution
- Bronchogenic
- Lobar
Aetiologic Agent
- Bacteria
- Virus
- Fungus
Mechanism
- Aspiration
- Community acquired
- Hospital acquired
Describe the patterns of bacterial pneumonia distribution
-
Bronchopneumonia
- Patchy consolidation of the lung.
-
Lobar pneumonia
- Consolidation of a large portion of a lobe or of an entire lobe.
Bronchopneumonia
- Common at the extremes of life.
- Patchy consolidation of the lung.
- Extension of a preexisting bronchitis.
Lobar Pneumonia
- Acute infection of an entire lobe.
- Usually due to a virulent organism.
- Abrupt onset.
- Now infrequent due to antibiotic treatment.
Describe the pathological findings and stages in lobar pneumonia
- Morphologic changes in the lung tend to follow a classic sequence.
- Four stages:
- Congestion
- Red hepatisation
- Grey hepatisation
- Resolution
- Since the introduction of antibiotics, this sequence is often altered.
Congestion
- Enlarged lobe.
- Heavy and congested with blood.
- Blood-stained fluid from the cut surface.
- Dilated alveolar capillaries.
- Air spaces filled with pale fluid.
- Scattered red blood cells and neutrophils.
- Occasional bacteria.
Red Hepatisation
- Cut surface is dry and red.
- Resembles liver macroscopically.
- Fluid containing fibrinogen has clotted in alveolar spaces.
- Increased numbers of neutrophils.
- Bacteria more numerous.
Grey Hepatisation
- After 2-3 days, loss of the red color.
- Starts at the hilum and moves out.
- Migration of large numbers of neutrophils.
- Decrease in capillary congestion.
- Virtual cessation of blood flow through the unventilated lobe.
Resolution
- Liquefaction of the previously solid exudate.
- Fibrinolytic enzymes.
- Apoptosis of neutrophils.
- Fluid contents removed:
- Expectoration
- Lymphatics.
- Takes several weeks.
Describe the symptoms and signs of bacterial pneumonia
ACUTE INFLAMMATION
- Fever
- Leukocytosis
- Cough - ALVEOLAR EXUDATE
- Sputum - ALVEOLAR EXUDATE
- Pleuritic chest pain - PLEURITIS
- Increased respiratory rate
- Cyanosis - HYPOXIA – V/Q MISMATCH
Describe the complications of bacterial pneumonia
- Complications may be seen in either bronchopneumonia or lobar pneumonia.
- Bronchopneumonia:
- Healing by fibrosis.
- Lobar pneumonia:
- Pleuritis
- Empyema
- Abscess formation
- Haematogenous seeding
- Death
Organisation / Fibrosis
- Healing by fibrosis rather than resolution is more common in bronchopneumonia.
- Leads to organizing pneumonia.
- Polyps of fibrous granulation tissue within alveoli.
- ‘Masson Bodies’.
Pleuritis
- Inflammation extends to involve the pleura.
- Gives rise to typical pleuritic pain.
- Initially may just be an effusion.
- Followed by fibrinous pleuritis +/- bacteria.
- Healing leads to fibrous adhesions between visceral and parietal pleura.
Abscess Formation
- Localized suppurative process characterized by necrosis of lung tissue.
- Associated with Staphylococcus Aureus and Klebsiella pneumoniae.
- Ranges from millimeters to centimeters.
- Can be single or multiple.
- Macro: Cavities filled with suppurative debris.
Abscess Formation Histology
- Florid inflammation.
- Destruction of alveolar walls.
- Liquefactive necrosis.
- Chronic abscess surrounded by fibrous tissue.
Empyema
- Collection of pus in the pleural cavity is called an empyema.
- Collection usually loculates, followed by scarring.
- Requires drainage.
- Heals by fibrosis.
Haematogenous Spread
- Dissemination of bacterial organisms throughout the lungs or other organs.
- Bacteraemia/septicaemia.
- Seeding to heart valves (bacterial endocarditis), meninges (meningitis), kidneys (pyelonephritis).
Haematogenous Seeding Examples
- Bacterial endocarditis with vegetations on the aortic valve.
- Brain with surface purulent exudate.
- Kidney with surface petechial haemorrhages.
- Meninges (Meningitis).
- Kidneys (Acute pyelonephritis).
Death
- Still one of the commonest causes of death.
- Especially in the very young and old.
- Often represents the terminal event secondary to some other debilitating process.
