How to Read a Chest X-Ray

Step 1 - Before You Look at the Film

• Patient ID - confirm name, date of birth, and date of the X-ray
• Clinical context - why was the film ordered? (cough, dyspnea, chest pain?)
• Compare with old films if available - this alone can change your interpretation

Step 2 - Assess Image Quality (RIP)

A poor-quality film means your interpretation must carry a disclaimer, and repeat imaging may be needed.

Step 3 - Systematic Anatomical Review (ABCDE)

A - Airway

• Is the trachea midline? Deviation suggests a tension pneumothorax (pushed away) or lung collapse/fibrosis (pulled toward).
• Check the carina - it should be a sharp angle (~60-70 degrees). Splaying of the carina suggests left atrial enlargement.
• Follow the main bronchi bilaterally.

B - Breathing (Lungs & Pleura)

• Lung fields: Do a rapid visual "ping-pong" comparison - left vs. right. Look for asymmetry, opacification, or hyperlucency.
• Lung parenchyma patterns to know:
  • Consolidation - dense white opacity, often with air bronchograms (pneumonia)
  • Interstitial pattern - diffuse fine lines (pulmonary edema, fibrosis)
  • Nodules/masses - nodules are 5-30 mm; masses are >30 mm
  • Cephalization of flow - enlarged upper lobe vessels = early heart failure
  • Vascular markings should stop 3-5 mm from the chest wall
• Pleura: Look for blunting of the costophrenic angles (pleural effusion) or a visible pleural line with absent lung markings (pneumothorax).
• Hilum: Normally the left hilum is higher than the right in ~70% of people. Bilateral hilar enlargement suggests sarcoidosis, lymphoma, or TB.

C - Cardiac/Circulation

• Cardiac size: On a PA view, the heart should be less than 50% of the transthoracic diameter (cardiothoracic ratio). Greater than 50% = cardiomegaly.
• Cardiac borders: Loss of a border = silhouette sign (pathology is in contact with that structure).
• Mediastinum: Width >8 cm at the aortic knob level is considered wide - think aortic dissection, lymphoma, or thymoma. If the mediastinal width exceeds 25% of the thoracic diameter at the carina level, it is abnormal.

D - Diaphragm

• The right hemidiaphragm is normally 2-20 mm higher than the left (stomach gas bubble beneath the left).
• Free air beneath the diaphragm = surgical emergency (bowel perforation) until proven otherwise.
• Blunted costophrenic angles = fluid.
• Elevated diaphragm = atelectasis, phrenic nerve palsy, subphrenic pathology.

E - Everything Else

• Bones: Rib fractures, lytic lesions, vertebral collapse, sclerotic changes (metastases).
• Soft tissues: Subcutaneous emphysema, breast shadows, skin folds.
• Lines and tubes: If present - check ETT position (2-5 cm above carina), central line tip (SVC/RA junction), NG tube (below diaphragm, not bronchus).

Step 4 - Check the Lateral View

• Review the spine - vertebral bodies should get gradually darker (more lucent) from top to bottom. Loss of this gradient = posterior consolidation.
• Anterior clear space (behind the sternum) - opacification suggests anterior mediastinal mass or fluid.
• Retrocardiac space - consolidation or mass here can only be seen on lateral.
• Diaphragms - the left ends at the anterior chest wall, the right passes all the way across.

Step 5 - The Silhouette Sign

Summary Checklist

1. Patient ID and clinical context
2. Image quality (RIP - rotation, inspiration, penetration)
3. Lateral view (spine, anterior space, retrocardiac space, diaphragms)
4. Bones and soft tissues
5. Mediastinum (width, trachea)
6. Cardiac silhouette (size, borders)
7. Diaphragms (level, free air)
8. Lungs: hila, parenchyma, pleura

• Pfenninger and Fowler's Procedures for Primary Care, 3rd ed., p. 1613
• Radiopaedia ABCDEF approach and Radiology Masterclass offer good supplementary visual guides.