A 62-year-old man with COPD presents with acute dyspnea and cough. Chest X-ray shows an area of increased opacity in the right lower lobe with air bronchograms and preserved volume. What is the most common cause of this radiological finding?

Question

Accepted Answer

C. Bacterial pneumonia. ## Consolidation: Definition and Etiology

**Key Point:** Consolidation is characterized by replacement of alveolar air with fluid, pus, blood, or cells, resulting in increased opacity with preserved lung volume and air bronchograms.

### Most Common Cause: Bacterial Pneumonia

Bacterial pneumonia is the most frequent cause of consolidation on chest X-ray, accounting for the majority of acute consolidative opacities in clinical practice.

### Radiological Features of Consolidation

| Feature | Present | Absent |
|---------|---------|--------|
| Air bronchograms | ✓ (pathognomonic) | — |
| Preserved volume | ✓ | — |
| Silhouette sign | ✓ (if lobar) | — |
| Increased opacity | ✓ | — |
| Mediastinal shift | ✗ | ✓ |

**High-Yield:** Air bronchograms (visible bronchi within opacified lung) are the hallmark of consolidation and indicate patent airways within consolidated parenchyma — this distinguishes consolidation from other causes of opacity.

### Differential Causes of Consolidation

1. **Infectious** (most common)
   - Bacterial pneumonia (pneumococcal, staphylococcal, gram-negative)
   - Viral pneumonia
   - Atypical pneumonia (mycoplasma, chlamydia)
   - Fungal (less common)

2. **Non-infectious**
   - Aspiration pneumonia
   - Pulmonary edema (cardiogenic)
   - Pulmonary infarction
   - Hemorrhage

**Clinical Pearl:** In an acute presentation with fever, cough, and consolidation, bacterial pneumonia should be the first diagnosis until proven otherwise. The presence of air bronchograms confirms alveolar filling rather than collapse.

### Why This Case Represents Consolidation, Not Collapse

- **Preserved volume** of the right lower lobe rules out atelectasis (collapse would reduce volume)
- **Air bronchograms** are present (pathognomonic for consolidation)
- **Acute presentation** in COPD patient with respiratory symptoms fits infectious etiology

[cite:Felson's Principles of Chest Roentgenology Ch 3]

Answer

A. Atelectasis

Answer

B. Pleural effusion

Answer

D. Pulmonary embolism

A 62-year-old man with COPD presents with acute dyspnea and cough. Chest X-ray shows an area of increased opacity in the right lower lobe with air bronchograms and preserved volume. What is the most common cause of this radiological finding?

Explanation

Consolidation: Definition and Etiology

Most Common Cause: Bacterial Pneumonia

Radiological Features of Consolidation

Differential Causes of Consolidation

Why This Case Represents Consolidation, Not Collapse

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Feature	Present	Absent
Air bronchograms	✓ (pathognomonic)	—
Preserved volume	✓	—
Silhouette sign	✓ (if lobar)	—
Increased opacity	✓	—
Mediastinal shift	✗	✓