Pathology 101 - Pneumonia

Jorvi Intensive Care by jsade

Background Reading

For normal histology and anatomy of the lungs, view Pathology 101 - Pulmonary Tumours.
To learn how to diagnose patients with pneumonia, consider reviewing clinical examination of the respiratory system. To refresh yourself on the symptoms and treatment, take a look at a brief rundown on Pneumonia. As always, Michelle (@eleytherius) has provided us with a quick snapshot.

 

Host Defence Mechanisms of the Respiratory System

• Physical Processes (e.g. Mucociliary escalator, particle expulsion, etc)
• Chemical Barriers (e.g. Mucus secreting goblet cells, α1-antitrypsin, etc)
• Cellular Mechanisms (e.g. Alveolar macrophages, NK Cells, etc)

Normal flora of the respiratory tract

• Streptococcus pneumonia
• Haemophilus influenza
• Diptheroids
• Staphylococcus aureus
• Moraxella catarrhalis
• Neisseria spp

Lower respiratory tract is normally sterile.

Pneumonia

Balancing Act

Aaron Sparshott

Ways to classify Pneumonia.

• Pathological Classification (air-space spread & interstitial spread)
• Morphological Classification
• Clinical Classification

 

Types of Pneumonia by Aaron Sparshott

Lobar & Broncho-pneumonia by Aaron Sparshott.
Adapted with gross morphology images by Pulmonary Pathology.

BACTERIAL PNEUMONIA
Pathogenesis

• Bacterial entry into alveoli and growth
• Tissue injury - injury to mucocilliary apparatus
• Inflammation - mΦs can be disrupted by EtOH, 
• Filling of alveolar spaces, spread to proximal alveoli - congestion can exacerbate CHF
• Systemic effects leading to fever and sepsis - G- (Endotoxin), G+ (cell wall) components

 Lobar Pneumonia

• Typically bilateral, widespread 
• Affects the young and healthy
• Caused by very virulent organisms (most commonly due to Strep. pneumoniae)
• Disease localized to an entire lobe of lung
• Fibrino-suppurative consolidation

4 Stages of Lobar Pneumonia

1. Congestion (24 hours - 2 days) - vascular engorgement, intra-alveolar fluid, few nΦ
2. Red Hepatization (2 - 4 days) - exudation, red cells, neutrophils and fibrin fill alveolar spaces
3. Grey Hepatization (4 - 8 days) - disintegration of red cells, persistence of fibrinosuppurative exudate
4. Resolution (after 8 days) - mΦs digest debris, organization by fibroblasts

Bronchopneumonia

• Affects the very young or old
• Patchy parenchymal involvement
• Multiple foci of consolidation 
• Bilateral and often widespread

Complications

1. Empyema - spread to pleural cavity - fibrinosuppurative rxn
2. Bacteremia dissemination - (e.g. IE, pericarditis, meningitis, etc)
3. Abscess formation - tissue destruction + necrosis
4. Organisation - convert regions to solid tissue

 CURD Guidelines for Severity (≥ 2 of the following → 36x risk of death)

• Confusion
• Urea >7 mmol/L
• Respiratory rate >30 /min
• Diastolic BP <60 mmHg 

Special Pneumonias

1. Viruses
2. Mycoplasma
3. Legionnaires (Legionella pneumophila / longbeachae / micdadei)
4. Meliodosis (Burkholderia pseudomallei)

 A collection of Pneumonia Tutorials

Aspiration Pneumonia

Early Pneumonia

Organizing Pneumonia

Interstitial pneumonia

Pneumocystis pneumonia

Aspiration pneumonia in an infant

References
Videos are thanks to  WashingtonDeceit. Material is sourced from my notes from pathology tutorials at UQ, and Robbin's Pathologic Basis of Disease. References for images are underneath the image.