---

How to Read a Chest X-Ray

---

Step 1 - Check Technical Quality First (RIPE)

• PA view - patient stands, X-ray beam goes from posterior to anterior. Best for outpatients; scapulae project outside lung fields.
• AP view - patient lies supine or sits in bed. Used for inpatients. The heart appears larger. Scapulae may overlie lung fields.

---

Step 2 - Systematic Review Using ABCDE

A - Airway

• Trace the trachea from above the clavicles down to the carina (at the level of the angle of Louis / T4-5).
• The trachea should be central or very slightly deviated to the right at the aortic arch.
• Tracheal deviation away from the affected side = tension pneumothorax or large pleural effusion.
• Tracheal deviation toward the affected side = lung collapse or fibrosis.
• The carina angle is normally less than 70°. Widening (>70°) suggests left atrial enlargement.
• Check the main bronchi bilaterally.

B - Breathing (Lung Fields)

• Consolidation - homogeneous opacity with air bronchograms; lobar or segmental; no volume loss
• Collapse/Atelectasis - opacity with volume loss (fissure displacement, mediastinal shift toward, raised hemidiaphragm)
• Pneumothorax - visible pleural line with absent lung markings beyond it
• Pleural effusion - homogeneous basal opacity with blunting of costophrenic angle; meniscus sign; needs ~200-500 mL to blunt the lateral costophrenic angle on an erect film (Grainger & Allison's Diagnostic Radiology)

C - Circulation (Heart and Great Vessels)

• Cardiac size: Cardiothoracic ratio (CTR) should be less than 50% on a PA film. A CTR > 50% suggests cardiomegaly. (Note: CTR is unreliable on AP films as the heart appears magnified.)
• Heart borders:
  • Right border = right atrium
  • Left border (top to bottom) = aortic knob, pulmonary artery, left atrial appendage, left ventricle
• Mediastinal width: A width greater than 8 cm at the level of the aortic arch raises concern for aortic injury or aneurysm; ratio > 0.38 (mediastinum:chest width) is suspicious (Tintinalli's Emergency Medicine).
• Aortic knob: Should be visible as a smooth, rounded left-sided opacity at the top of the mediastinum.
• Check for pulmonary vascular redistribution (upper lobe diversion = left heart failure), perihilar bat-wing" haziness (pulmonary oedema), or Kerley B lines (horizontal lines at periphery of lower lung = interstitial oedema).

D - Diaphragm

• Both hemidiaphragms should appear as smooth, convex upward domes (Grainger & Allison's Diagnostic Radiology).
• The right hemidiaphragm is normally higher than the left by ~15 mm (up to 30 mm in 90% of people). The gastric fundus should be visible below the left dome.
• The costophrenic angles should be sharp and acute. Blunted angles indicate pleural fluid or scarring.
• Raised hemidiaphragm = phrenic nerve palsy, subphrenic pathology, lower lobe collapse.
• Flattened diaphragms = emphysema, acute severe asthma (depression occurs in both; flattening only in emphysema).
• Free air under the diaphragm = bowel perforation (pneumoperitoneum). Best seen on an erect film.
• Look for diaphragm inversion - seen with tension pneumothorax, large basal bullae, or large pleural effusions.

E - Everything Else (Bones and Soft Tissues)

• Clavicles, scapulae, ribs (count both posteriorly and anteriorly)
• Look for rib fractures (especially multiple, suggesting flail chest), lytic or sclerotic lesions, and rib notching (coarctation of aorta)
• Fractures of the 1st/2nd ribs or bilateral clavicles raise suspicion for aortic rupture (Bailey and Love's Surgery)
• Lower rib fractures suggest liver or splenic injury

• Look for subcutaneous emphysema (gas in soft tissues)
• Check for breast shadows - asymmetric absence may indicate prior mastectomy (important not to mistake for lung pathology)
• Check for pacemakers, lines, drains, surgical clips

---

Step 3 - Review Areas Commonly Missed

---

Step 4 - Correlate Clinically

• What was the clinical indication for the film?
• Does the radiographic finding explain the symptoms?
• Are there lines, tubes, drains in the correct position?
  • Endotracheal tube: tip should be 2-3 cm above the carina
  • Central venous line: tip in the superior vena cava or right atrium junction
  • Chest drain: within the pleural space, pointing toward the apex (for pneumothorax) or base (for effusion)
• Compare with prior films - a subtle new change may be the only finding

---

Quick Summary Mnemonic

ABCDE - Airway, Breathing (lungs), Circulation (heart/vessels), Diaphragm, Everything else (bones/soft tissue)

Before ABCDE, always check RIPE (Rotation, Inspiration, Projection, Exposure)

---

Common Chest X-Ray Findings at a Glance

---

• Grainger & Allison's Diagnostic Radiology (chest radiograph anatomy, pleural effusion, diaphragm)
• Tintinalli's Emergency Medicine (mediastinal widening, chest radiograph in trauma)
• Bailey and Love's Short Practice of Surgery (rib fractures, thoracic injury)