85 - Pathology of Lung Infection Flashcards
Most important determinant of whether a lung infection becomes clinical or not
Intact immune system
What causes classical pattern of pneumonia?
Traditional bacteria
- Aerobic bacteria, known to medicine for a long time (as can be cultured easily)
S pneumoniae, H influenzae, Klebsiella pneumoniae, P aerusinosa, Legionella pneumophila
Strict definition of pneumonia
Inflammation of the lung
Two patterns of acute bacterial pneumonia
Acute bronchopneumonia
Acute lobar pneumonia
Most common form of acute inflammation of the lung
Acute bronchopneumonia
Prototypical atypical bacteria causing pneumonia
Mycoplasma
Patients with a much higher risk of G- bacterial pneumonia
Those who acquire it in a hospital
When was acute lobar pneumonia more common?
Pre-antibiotic era
Five principle defence mechanisms of the lung
Cough reflex Mucociliary function Secretion clearance Alveolar macrophage phagocytic action Clearance of fluid from pulmonary circulation
Five principle ways in which lung defences can be subverted
Loss of cough reflex
Impairment of mucociliary function
Accumulation of secretions (EG: CF)
Interference with alveolar macrophage function
Pulmonary oedema/congestive heart failure
How does bronchopneumonia present grossly?
Discrete patches of inflammation (spots), not necessarily limited by lobes.
Often bilateral.
Where does bronchopneumonia begin?
In terminal bronchioles, hence multifocal distribution.
How does lobar pneumonia begin?
Inflammatory oedema spreads throughout a lobe.
Indicative of a highly-pathogenic organism.
Difference in virulence of organisms that cause bronchopneumonia and lobar pneumonia
Bronchopneumonia often caused by less-pathogenic pathogens.
Most-common cause of lobar pneumonia
S pneumoniae
Second-most-common cause of lobar pneumonia
H influenzae
Pneumonia more likely to cause inflammation of the pleura
Lobar
Difference in auscultation between bronchopneumonia and lobar pneumonia
Bronchial breath sounds heard over area of lobar pneumonia
Consolidation
Filling of alveolar spaces with fluid or inflammatory cells. Lung becomes harder to compress, harder.
*ALVEOLARSLIDE NO LABELS
ALVEOLAR SLIDE
Appearance of a histological slide of acute bronchopneumonia
Exudate from inflammation moves from alveolar septa into alveolar space.
Alveolar spaces full of inflammatory cells, protein-rich exudate.
Areas of lots of neutrophils are full of pus.
Blood vessels are thicker, from vasodilation.
What does bronchopneumonia lung consolidation look like grossly?
Pale, solid areas are areas of consolidation.
What does lobar pneumonia consolidation look like grossly?
Entire lobe is pale, hard.
Red hepatisation initially, grey hepatisation develops over time (because consolidated lung apparently looks like a cut surface of a liver).
Why does red hepatisation develop before grey hepatisation?
Because early lobar pneumonia involves more haemorrhage.
Becomes white as neutrophils infiltrate, form pus.
How does a lobar pneumonia appear on a CXR
Pale, solid.
Condition where puss-filled cavities form in lung
Lung abscess
Abscess
A collection of pus
Causes of lung abscesses 1 2 3 4 5
Aspiration
Obstruction of the bronchial tree
Haematogenous seeding of the lung from an extra-pulmonary infection (EG: osteomyelitis)
Certain kinds of bacterial pneumonia (S pyogenes, S aureus, Klebsiella pneumoniae)
Acute bronchopneumonia in debilitated hosts.
Most important cause of lung abscesses
Aspiration of vomit when supine, asleep.
What should you search for when theres an abscess caused by obstruction?
Bronchial carcinoma
Kind of infection from aspiration
Mixed anaerobic infection (bacteroides)
Key difference between viral and bacterial pneumonias
Viral don’t cause consolidation.
Exudate from viral is lymphocyte-rich. Exudate from bacterial is neutrophil-rich.
Type of oedema from viral pneumonias
A lot of exudate, but not purulent consolidation.
How do viral pneumonias predispose to secondary bacterial pneumonias?
Cytopathic - destroy epithelial cells.
Cause death of epithelial cells within the upper and lower respiratory tract, predisposing to secondary bacterial infections and severe pulmonary oedema
Aetiological agent leading to lymphocytic bronchiolitis
Viral, leading to pneumonia
Bronchiectasis
Dilation of large, cartilage-containing airways.
Permanent, irreversible.
What causes bronchiectasis
Scar tissue deposition around the bronchi, weakening of bronchial walls from inflammation.
Gross appearance of bronchiectasis
Very dilated (almost cyst-like) bronchi. White sections surrounding bronchi (scar tissue)
Aetiological agent leading to bronchiectasis
Chronic bacterial infection.
Inflammatory exudate weakens bronchial wall.
Scar tissue deposits, widens bronchi as it contracts.
Pooling of secretion.
Complications of bronchiectasis 1 2 3 4 5 6
1) Copious, offensive sputum production
2) Poor drainage of secretions, leading to recurrent bacterial pneumonia and abscesses.
3) Ruputure of vessels in bronchial walls, leading to haemoptysis
4) Pulmonary fibrosis leading to cor pulmonale
5) Cerebral abscesses (haematogenous spread of pathogen from lungs to brain)
6) Amyloidosis (very rare)
