What are the key findings to look for on a chest X-ray (CXR) for pneumonia (PNA)?

Key Chest X-Ray Findings for Pneumonia

Look for consolidation (alveolar opacities/infiltrates) as the primary radiographic finding for pneumonia, along with ground-glass opacities, air bronchograms, and parapneumonic effusions—but remember that a normal CXR does NOT rule out pneumonia, especially early in the disease course. 1, 2

Primary Radiographic Findings to Identify

Consolidation Patterns

• Alveolar opacities or infiltrates appearing as areas of increased density that obscure underlying lung markings—this is the most reliable finding for pneumonia diagnosis 2
• Air bronchograms are highly specific (96%) when present, especially if single, indicating severe alveolar filling 2
• Patchy or confluent lesions distributed along the pleura, with the lower right lobe most frequently affected, followed by upper and lower left lobes 2

Ground-Glass Opacities

• Hazy areas that partially obscure underlying lung markings—commonly seen in viral pneumonias including COVID-19 1, 2
• Bilateral interstitial pattern with ground-glass opacities is characteristic of viral pneumonias 2

Associated Findings

• Parapneumonic effusions occur in 10-32% of pneumonia cases—both PA and lateral views are superior to AP radiography for detecting these 1, 2
• Interlobular septal thickening creating grid-like opacities, particularly in viral pneumonia 2

Critical Imaging Approach

Optimal Technique

• Obtain upright PA and lateral chest radiographs when feasible—this is the reference standard and superior to AP portable radiography 1
• Lateral views may reveal infiltrates not visible on frontal projections alone 2

Temporal Considerations

• Initial CXR shows typical pneumonia appearances in only 36% of cases 2, 3
• Repeat CXR after 24-48 hours if clinical suspicion remains high despite negative initial imaging 2, 3
• For COVID-19, severity of imaging findings peaks at 10-12 days from symptom onset 1

Integration with Clinical Assessment

When CXR is Most Useful

• Abnormal vital signs: temperature ≥38°C, respiratory rate >24/min, heart rate >100/min 3
• Physical examination findings: crackles, rhonchi, decreased breath sounds, egophony, or fremitus 1
• Laboratory markers: C-reactive protein >100 mg/L, leukocytosis, elevated procalcitonin 1

Special Populations

• Elderly patients and those with dementia: >75% may have pneumonia on CXR despite normal vital signs and physical examination 1
• Patients with organic brain disease (stroke, delirium) warrant CXR regardless of examination findings 1

Critical Pitfalls to Avoid

Do Not Rely Solely on CXR

• CXR sensitivity ranges only 43.5-69% compared to CT 3
• A normal CXR does NOT exclude pneumonia, particularly early in disease 1, 2, 3
• The false-negative rate is substantial in early disease 3

Specificity Limitations

• Overall radiographic specificity of pulmonary opacity for pneumonia is only 27-35% 2
• Must distinguish from non-infectious causes: atelectasis, pulmonary edema, pulmonary embolism, organizing pneumonia, pulmonary contusion, hemorrhage 2

Technical Limitations

• Poor-quality portable films in hospitalized patients compromise diagnostic accuracy 2
• CXR has difficulty detecting central infections not adjacent to pleura 1

Alternative Imaging When CXR is Negative

Lung Ultrasound

• Superior sensitivity (93-96%) and specificity (93-96%) compared to CXR 1, 2
• Consider when CXR is negative but clinical suspicion remains high 2
• Limited by subcutaneous emphysema, obesity, thick chest wall, and inability to detect central infections 1

CT Chest

• Detects pneumonia in 27-33% of cases with negative CXR 2, 3
• Reserve for hospitalized patients with high risk factors, increased comorbidities, or suspected complications 1
• Not recommended as initial screening tool 2