How do you interpret a chest X-ray (CXR)?

How to Interpret a Chest X-Ray

Chest X-ray interpretation requires a systematic, structured approach that evaluates all anatomical compartments in a specific sequence to avoid missing critical findings.

Systematic Approach to CXR Interpretation

A standardized method is essential because unsystematic review leads to false negative rates of 20-30% and false positive rates of 2-5% 1. The most commonly missed findings occur in the retrocardiac area, chest wall-mediastinum border, and within the mediastinum itself 1.

Step-by-Step Interpretation Algorithm

Evaluate these structures in order:

• Technical factors first: Assess patient positioning, degree of inspiration (diaphragm should be at the 9th-10th posterior rib), rotation (clavicular heads equidistant from spinous processes), and penetration 2

• Soft tissues: Examine chest wall, subcutaneous emphysema, breast shadows 2

• Bones: Review ribs, clavicles, scapulae, spine, and shoulder girdle for fractures, lytic or blastic lesions 2

• Pleura: Look for pneumothorax, pleural effusions, pleural thickening 2

• Mediastinum: Assess width, contours, tracheal position, and mediastinal masses 2

• Cardiac silhouette: Evaluate size (cardiothoracic ratio <0.5 on PA view), borders, and chamber enlargement 2

• Pulmonary vasculature and hila: Examine hilar size and contours; the right interlobar artery should be ≤15 mm in women and ≤16 mm in men 3

• Lung fields: Systematically review all zones (upper, middle, lower) in both lungs for infiltrates, masses, nodules, or hyperinflation 2

• Diaphragm: Check position, contour, and costophrenic angles 2

• Medical devices: If present, verify positioning and look for device-related complications 4

Key Radiographic Patterns and Their Significance

Pulmonary Hypertension Signs

• Central pulmonary artery enlargement with rapid peripheral tapering ("pruning") 3
• Right heart chamber enlargement visible on lateral view as retrosternal space encroachment 3
• Main pulmonary artery prominence occurs in 90% of pulmonary arterial hypertension patients 3
• However, CXR has limited sensitivity for mild pulmonary hypertension; a normal CXR does not exclude the diagnosis 3

Hyperexpanded Lungs

• Flattened diaphragms with increased lung volumes 5
• Increased retrosternal airspace on lateral view 5
• Widened intercostal spaces 5
• These findings indicate obstructive lung disease (COPD, asthma, cystic fibrosis) and require pulmonary function testing for confirmation 5

Critical Limitations of CXR

CXR has poor sensitivity for detecting pulmonary metastases, with sensitivity as low as 28% compared to chest CT 3. Small peripheral nodules are particularly difficult to detect 3. For cancer staging or suspected metastatic disease, chest CT with IV contrast is the appropriate imaging modality, not CXR 3.

Common Pitfalls to Avoid

• Failing to compare with prior studies: This is essential for detecting subtle changes and avoiding false interpretations 1

• Not using lateral projections: Lateral views are critical for precise localization of abnormalities 1

• Ignoring clinical context: Knowledge of patient history and symptoms significantly reduces interpretation errors 1

• Overlooking the "hidden areas": Pay extra attention to retrocardiac regions, apices, lung bases behind the diaphragm, and areas obscured by medical devices 1

• Accepting suboptimal technical quality: Poor positioning, inadequate inspiration, or improper exposure directly impairs diagnostic accuracy 6, 7

When CXR Is Insufficient

Proceed to advanced imaging when:

• Suspected pulmonary metastases (use chest CT) 3
• Pulmonary hypertension suspected but CXR normal (use echocardiography) 3
• Hyperexpanded lungs requiring characterization of emphysema (use high-resolution CT) 5
• Clinical suspicion remains high despite normal CXR 3, 1