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

Systematic Approach to Chest X-Ray Interpretation

Interpret a chest X-ray using a consistent, systematic approach that evaluates technical quality first, followed by sequential assessment of airways, bones, cardiac silhouette, diaphragm, lung fields, mediastinum, and pleural spaces—recognizing that CXR has significant limitations in detecting small nodules, ground-glass opacities, and lesions obscured by anatomical structures. 1

Technical Quality Assessment

Begin by confirming adequate technical factors before interpretation:

• Rotation: Check if the medial ends of the clavicles are equidistant from the spinous processes 2
• Inspiration: Count posterior ribs—adequate inspiration shows 8-10 posterior ribs visible above the diaphragm 2
• Penetration: The vertebral bodies should be just visible through the cardiac silhouette 2
• Positioning: Verify if posteroanterior (PA), anteroposterior (AP), or lateral view 2

Systematic Review Pattern (ABCDEFGH Approach)

Airways

• Evaluate tracheal position and caliber for deviation or narrowing 2
• Assess main bronchi for patency and symmetry 2

Bones and Soft Tissues

• Examine ribs, clavicles, scapulae, and visible spine for fractures or lytic lesions 2
• Review soft tissues for subcutaneous emphysema or masses 2

Cardiac Silhouette

• Measure cardiothoracic ratio (should be <0.5 on PA film) 3
• In pulmonary hypertension, look for right heart chamber enlargement 3
• Assess cardiac borders for clarity (silhouette sign indicates adjacent consolidation) 2

Diaphragm

• Confirm smooth, dome-shaped contours 2
• Right hemidiaphragm normally sits 1-2 cm higher than left 2
• Look for free air under diaphragm (pneumoperitoneum) 4

Lung Fields and Effusions

• Compare symmetry between right and left lungs 2
• Assess for consolidation, masses, nodules, or infiltrates 5
• Examine costophrenic angles for blunting (pleural effusion) 5, 4

Mediastinum and Hila

• Evaluate mediastinal contours and width 4
• In pulmonary hypertension, measure right interlobar artery: >15 mm in women or >16 mm in men suggests PH 3
• Look for hilar enlargement or lymphadenopathy 3

Hidden Areas (Common Pitfall Zones)

• Apices: Often missed location for small nodules or pneumothorax 1, 2
• Behind heart: Lesions obscured by cardiac silhouette require lateral view 1, 2
• Below diaphragm: Check for pneumoperitoneum 4
• Lung periphery: Small peripheral nodules easily missed 1

Critical Limitations to Recognize

CXR has inherently poor sensitivity for many pathologies—you must understand when to escalate to CT imaging:

Detection Limitations

• Sensitivity for pulmonary metastases is only 28% compared to CT 3, 1
• Misses small nodules: CXR detected only 68 nodules versus 233 on CT in screening studies 1
• Cannot reliably detect ground-glass opacities, bronchial wall thickening, or small consolidations 1
• Normal CXR in 49 of 166 confirmed acute respiratory infections on CT 1
• Up to 34% of CT-proven bronchiectasis shows normal CXR 1

Anatomical Blind Spots

• Lesions behind heart, mediastinum, diaphragm, and bony structures are commonly missed 1
• Lateral view reveals 15% of lung hidden on PA film 2

Specific Disease Contexts

Pulmonary Hypertension: CXR findings include enlarged central pulmonary arteries with pruning, right heart enlargement, and right interlobar artery >15-16 mm, but normal CXR does not exclude mild PH 3

Tuberculosis: Machine learning studies show CXR can achieve 89-96% accuracy, but human interpretation has substantial inter-observer variability 3

Pneumothorax, Pneumonia, Heart Failure, Pleural Effusion: AI tools are being developed to assist emergency detection of these conditions 5

Essential Practice Points

• Always compare with prior films when available to identify subtle changes 2
• Read the CXR yourself first before reviewing the radiology report to develop interpretive skills 2
• Use the same systematic approach every time to avoid missing findings 2
• Consider lateral view routinely, as it reveals pathology hidden on PA view 2
• Recognize when CXR is insufficient: Persistent symptoms with normal CXR warrant CT imaging 3, 1
• Interpreter skill matters significantly: Even visible lesions can be missed due to perceptual errors 1

When to Escalate to CT

Order chest CT instead of or in addition to CXR when:

• Screening for pulmonary metastases in cancer patients 3
• Evaluating suspected pulmonary hypertension with persistent symptoms despite normal CXR 3
• Detecting small pulmonary nodules or early lung cancer 1
• Assessing interstitial lung disease or bronchiectasis 1
• Patient has high-risk smoking history warranting lung cancer screening 3

CT provides superior spatial resolution and contrast, detecting pathology that CXR routinely misses 3, 1.