Identifying Various Pneumonias on Chest X-Ray
Chest radiography remains the primary imaging modality for identifying pneumonia, with specific radiographic patterns often suggesting particular etiologies when correlated with clinical information. 1, 2
Key Radiographic Patterns of Pneumonia
Community-Acquired Pneumonia (CAP)
- Lobar Consolidation: Air-space consolidation limited to one lobe or segment
- Typically homogeneous opacity with air bronchograms
- Sharp borders when confined by fissures
- Most commonly seen with Streptococcus pneumoniae 3
- Bronchopneumonia Pattern:
- Patchy, multifocal opacities
- Often bilateral and predominantly in lower lobes
- Common with Haemophilus influenzae, Staphylococcus aureus 1
- Interstitial Pattern:
- Reticular or reticulonodular opacities
- Often associated with atypical pathogens (Mycoplasma, viral)
Hospital-Acquired Pneumonia
- Multifocal, Diffuse Involvement
- Pleural Effusions more common
- Rapid Progression of infiltrates
- Cavitation more frequent (especially with Pseudomonas, Klebsiella) 1, 3
Aspiration Pneumonia
- Dependent Segments involvement (posterior segments of upper lobes, superior/basal segments of lower lobes)
- Bilateral Multicentric Opacities
- Right Lung more commonly affected than left 3
Epidemiologic Factors Affecting Radiographic Presentation
| Patient Factor | Common Radiographic Finding | Likely Pathogens |
|---|---|---|
| Alcoholism | Right lower lobe consolidation | S. pneumoniae, anaerobes, gram-negative bacilli |
| COPD/Smoker | Patchy bronchopneumonia | H. influenzae, M. catarrhalis, Legionella |
| Nursing Home | Multilobar involvement | S. pneumoniae, gram-negative bacilli, S. aureus |
| Influenza Active | Bilateral interstitial pattern | Influenza, secondary S. pneumoniae, S. aureus |
| Aspiration Risk | Dependent segment opacities | Anaerobes, chemical pneumonitis |
| Structural Lung Disease | Cavitary lesions | P. aeruginosa, S. aureus |
Limitations of Chest X-Ray
- Sensitivity Issues: May miss early pneumonia
- Up to 30% of early pneumonias may not be visible on initial radiographs
- Consider CT in high clinical suspicion with negative X-ray 2
- Interpretation Variability: Significant inter-observer variation in radiograph interpretation 4
- Technical Factors: Quality affected by patient positioning, inspiration depth, and portable technique 1
Advanced Imaging Considerations
CT Indications:
Ultrasound Applications:
Specific Radiographic Findings by Pathogen
- Streptococcus pneumoniae: Homogeneous lobar consolidation with air bronchograms
- Klebsiella pneumoniae: Upper lobe consolidation with bulging fissures, potential cavitation
- Staphylococcus aureus: Patchy bronchopneumonia, rapid progression, pneumatoceles, abscesses
- Legionella: Asymmetric patchy infiltrates progressing to consolidation, often lower lobe
- Mycoplasma: Reticular interstitial pattern, often worse than clinical presentation
- Viral pneumonia: Bilateral interstitial pattern, peribronchial thickening
Approach to Radiographic Diagnosis
- Assess Distribution: Lobar vs. bronchopneumonic vs. interstitial
- Evaluate Extent: Single lobe vs. multilobar vs. bilateral
- Look for Complications: Effusion, cavitation, pneumatocele, abscess
- Consider Patient Factors: Age, comorbidities, immune status
- Correlate with Clinical Presentation: Onset, severity, associated symptoms
Common Pitfalls to Avoid
- Failing to obtain both PA and lateral views when possible (single-view AP has lower sensitivity) 1
- Overlooking pneumonia in areas of underlying lung disease
- Misinterpreting atelectasis as pneumonia
- Not considering non-infectious causes of consolidation
- Inadequate follow-up imaging to monitor resolution 2
By systematically evaluating chest radiographs and correlating findings with clinical information, clinicians can more accurately identify various pneumonias and guide appropriate management.