How to Read a Chest X-Ray

Normal PA (A) and lateral (B) chest X-ray of a healthy subject - Harrison's Principles of Internal Medicine, 22E

Step 0 - Before You Even Look at the Image

• Patient details: Name, date of birth, date/time of the film
• Clinical context: Why was this ordered? What are you looking for?
• Comparison films: Pull up the prior CXR if available - changes over time are often more important than a single snapshot

Step 1 - Assess Image Quality (RIPE)

Step 2 - Systematic Reading (ABCDE Approach)

A - Airway

• Trachea: Should be midline. Deviation can be caused by:
  • Pushed away: tension pneumothorax, large pleural effusion, mass
  • Pulled toward: lung collapse, fibrosis, pneumonectomy
• Carina: Check the carina angle (normally < 70°). Wide angle suggests left atrial enlargement.
• Main bronchi: Trace the left and right main bronchi branching from the carina.

B - Breathing (Lung Fields)

C - Cardiac

• Size: Cardiothoracic ratio (CTR) = maximum horizontal cardiac diameter / maximum horizontal thoracic diameter. Should be < 0.5 on a PA film. A CTR > 0.5 suggests cardiomegaly (pericardial effusion, dilated cardiomyopathy, etc.).
  • Do not apply this on AP films - the heart is magnified.
• Shape: Boot-shaped heart (RVH), flask-shaped (pericardial effusion), prominent left heart border
• Heart borders:
  • Right border = right atrium
  • Left upper border = aortic knuckle + pulmonary artery
  • Left lower border = left ventricle

D - Diaphragm

• Right hemidiaphragm is normally higher than the left (liver underneath).
• Check for:
  • Elevated hemidiaphragm: phrenic nerve palsy, subphrenic abscess, collapse/consolidation of lower lobe, hepatomegaly
  • Flattened diaphragm: COPD hyperinflation
  • Free air under the diaphragm: perforated viscus (surgical emergency!)
  • Costophrenic angles: should be sharp. Blunting = pleural effusion (at least ~200-300 mL to blunt the angle on PA view)

E - Everything Else (Extras)

Hila

• Left hilum is normally 0.5-1.5 cm higher than the right.
• Bilateral hilar enlargement: sarcoidosis, lymphoma, bilateral malignant nodes, pulmonary arterial hypertension
• Unilateral hilar enlargement: lymphoma, malignancy, infection

Mediastinum

• Superior mediastinum: check for widening (aortic dissection, lymphoma, retrosternal goitre)
• Anterior: thymoma, teratoma, "terrible lymphoma" ("4 Ts")
• Middle: pericardial cyst, lymph nodes
• Posterior: neurogenic tumors, esophageal pathology

Bones

• Rib fractures (look for steps or discontinuity)
• Rib notching (coarctation of the aorta - inferior rib margin erosions, usually sparing ribs 1-2)
• Lytic or sclerotic lesions (metastases, myeloma)
• Vertebral collapse
• Shoulder and clavicle pathology

Soft Tissues

• Subcutaneous emphysema (surgical emphysema - bubbly appearance in soft tissues)
• Breast shadows (absent breast shadow = previous mastectomy)
• Foreign bodies, pacemakers, central lines, ETT

Step 3 - Devices and Lines (If Present)

Quick Reference: Common Patterns

Practical Tips

1. Always use the same sequence - it doesn't matter which order, but being consistent prevents you from skipping things.
2. Compare sides - asymmetry is often the clue.
3. Context is king - the same opacity can be pneumonia or malignancy depending on the patient.
4. Look at the edges - apices, costophrenic angles, and behind the heart are common areas where abnormalities are missed.
5. A normal CXR doesn't rule out serious pathology - a PA film misses around 20-25% of pulmonary nodules < 1 cm.

Important Disclaimer

Looking at Your Image

Most Likely Diagnosis: Allergic Contact Dermatitis (ACD) from Mango Tree Sap

Why Mango?

"Mango dermatitis is uncommon in natives of mango-growing countries who have never been exposed to Toxicodendron species. Many persons who have been so exposed are sensitized by one or a few episodes of contact with the peel of the mango fruit."

"Mango (Mangifera indica) and cashew (Anacardium occidentale) are common foods with urushiol-like compounds. In sensitized individuals, reexposure can result in urticaria and pruritus. Over 12 to 48 hours, symptoms may progress to varying degrees of vesiculobullous formation."

Treatment Plan

Step 1 - Upgrade the Steroid (Most Important)

Step 2 - Oral Antihistamine (for Itch Relief)

Step 3 - Wash the Area Well

Step 4 - Keep the Area Cool and Dry

When to See a Doctor Urgently

• Blisters start forming or rash becomes weeping/oozing
• Rash spreads to your face, eyes, or genitals
• Fever develops
• The rash does not improve within 5-7 days of proper treatment
• Swelling around the rash increases

Prevention Going Forward

• Wear long sleeves and gloves when picking mangoes
• Wash exposed skin immediately after contact with mango sap
• You are now sensitized - future exposure will cause faster, possibly more severe reactions