A 35-year-old previously healthy woman presents with acute onset fever, pleuritic chest pain, and productive cough with rusty sputum. Chest X-ray shows consolidation of the entire right lower lobe with air bronchograms. Which of the following is NOT consistent with lobar pneumonia?

Explanation

## Pathogenesis and Features of Lobar Pneumonia **Key Point:** Lobar pneumonia is characterized by **uniform consolidation of an entire anatomical lobe** with **fibrinous exudate filling alveolar spaces**, typically caused by S. pneumoniae. The process begins in alveoli and spreads through collateral channels, NOT through bronchioles. ### Pathogenesis of Lobar Pneumonia 1. **Inhalation** of S. pneumoniae into distal alveoli 2. **Alveolar inflammation** with fibrinous exudate accumulation 3. **Spread** through pores of Kohn and canals of Lambert to adjacent alveoli 4. **Uniform consolidation** of entire lobe or segment 5. **Resolution** with fibrinolysis and resorption of exudate **High-Yield:** The critical distinction is the **site of origin**: lobar pneumonia begins in **alveolar spaces** (not bronchioles), and spreads through **pores of Kohn** (not bronchi). ### Comparison: Lobar vs Bronchopneumonia | Feature | Lobar Pneumonia | Bronchopneumonia | |---------|-----------------|------------------| | **Site of origin** | Alveolar spaces | Terminal bronchioles | | **Spread mechanism** | Pores of Kohn, canals of Lambert | Through bronchi to alveoli | | **Distribution** | Segmental/lobar, uniform | Patchy, multifocal, non-segmental | | **Exudate type** | Fibrinous | Purulent | | **Common organism** | S. pneumoniae | S. aureus, gram-negatives | | **Clinical onset** | Acute, sudden | Insidious, gradual | **Clinical Pearl:** Rusty sputum (blood-tinged) is a classic sign of lobar pneumonia and reflects fibrinous exudate with hemorrhage — not seen in bronchopneumonia. ### Why Option 2 is Incorrect Option 2 describes the pathogenesis of **bronchopneumonia**, not lobar pneumonia. In bronchopneumonia, inflammation originates in terminal bronchioles and extends to surrounding alveoli in a patchy pattern. In lobar pneumonia, the process begins directly in alveolar spaces and spreads through pores of Kohn. ### Correct Features of Lobar Pneumonia (Options 0, 1, 3) - **Option 0:** ✓ Correct. Lobar pneumonia begins in alveolar spaces and spreads through pores of Kohn. - **Option 1:** ✓ Correct. Fibrinous exudate uniformly fills alveoli throughout the affected lobe. - **Option 3:** ✓ Correct. S. pneumoniae is the classic causative organism of lobar pneumonia.