A 68-year-old man with a 40-year smoking history presents with acute onset fever (39.5°C), productive cough with purulent sputum, and pleuritic chest pain for 3 days. On examination, he has consolidation with bronchial breath sounds over the left lower lobe. Chest X-ray shows a homogeneous opacity confined to the left lower lobe with air bronchograms. Sputum culture grows Streptococcus pneumoniae. What is the most likely diagnosis?

Question

Accepted Answer

B. Lobar pneumonia. ## Diagnosis: Lobar Pneumonia ### Clinical Presentation Analysis **Key Point:** The constellation of acute onset, consolidation confined to a single anatomical lobe, homogeneous opacity with air bronchograms, and isolation of S. pneumoniae are hallmark features of lobar pneumonia. ### Pathological Features of Lobar Pneumonia | Feature | Lobar Pneumonia | Bronchopneumonia | |---------|-----------------|------------------| | **Onset** | Sudden, acute | Insidious | | **Distribution** | Single lobe or segment | Patchy, multifocal, bilateral | | **Radiological pattern** | Homogeneous consolidation with air bronchograms | Scattered infiltrates around bronchi | | **Pathology** | Alveolar filling with fibrin, RBCs, WBCs, bacteria | Inflammation of bronchi with surrounding alveolar involvement | | **Common organism** | S. pneumoniae, S. pyogenes | H. influenzae, S. aureus, Gram-negatives | | **Clinical course** | Rapid progression, crisis (defervescence) | Slow, insidious, gradual recovery | | **Pleural involvement** | Fibrinous pleuritis common | Rare | ### Why This Is Lobar Pneumonia 1. **Anatomical distribution:** Consolidation strictly confined to left lower lobe (not patchy or multifocal) 2. **Radiological appearance:** Homogeneous opacity with air bronchograms — classic for lobar pneumonia 3. **Organism:** S. pneumoniae is the classic causative agent of lobar pneumonia 4. **Acute presentation:** Sudden onset with pleuritic chest pain and high fever 5. **Physical findings:** Bronchial breath sounds and consolidation on percussion indicate alveolar filling **High-Yield:** Lobar pneumonia follows a predictable pathological sequence: congestion → red hepatization → gray hepatization → resolution. This is why the radiological appearance is so characteristic. **Clinical Pearl:** The presence of air bronchograms (dark branching lines within the opacity) indicates patent airways within consolidated lung — this is pathognomonic for alveolar filling and rules out pure bronchial inflammation. ### Pathological Stages of Lobar Pneumonia ```mermaid flowchart TD A[Acute Infection by S. pneumoniae]:::action --> B[Stage 1: Congestion
24 hrs]:::outcome B --> C[Stage 2: Red Hepatization
2-3 days]:::outcome C --> D[Stage 3: Gray Hepatization
4-6 days]:::outcome D --> E[Stage 4: Resolution
7-10 days]:::outcome E --> F[Complete recovery]:::action ``` **Key Point:** Each stage corresponds to specific histopathological changes: fibrin deposition, RBC exudation, WBC infiltration, and eventual organization/resolution.

Answer

A. Aspiration pneumonia

Answer

C. Atypical pneumonia

Answer

D. Bronchopneumonia

Explanation

Diagnosis: Lobar Pneumonia

Clinical Presentation Analysis

Pathological Features of Lobar Pneumonia

Why This Is Lobar Pneumonia

Pathological Stages of Lobar Pneumonia

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Feature	Lobar Pneumonia	Bronchopneumonia
Onset	Sudden, acute	Insidious
Distribution	Single lobe or segment	Patchy, multifocal, bilateral
Radiological pattern	Homogeneous consolidation with air bronchograms	Scattered infiltrates around bronchi
Pathology	Alveolar filling with fibrin, RBCs, WBCs, bacteria	Inflammation of bronchi with surrounding alveolar involvement
Common organism	S. pneumoniae, S. pyogenes	H. influenzae, S. aureus, Gram-negatives
Clinical course	Rapid progression, crisis (defervescence)	Slow, insidious, gradual recovery
Pleural involvement	Fibrinous pleuritis common	Rare