Chest xray how to read
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how to read a chest X-ray systematic approach
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systematic approach to reading chest X-ray
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How to Read a Chest X-Ray
Step 0 - Before You Even Look at the Image
Always check:
- 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)
Before interpreting any findings, confirm the film is technically adequate. Use the mnemonic RIPE:
| Letter | Stands for | What to check |
|---|---|---|
| R | Rotation | Medial ends of clavicles should be equidistant from the spinous processes. A rotated film can falsely suggest tracheal deviation or cardiomegaly. |
| I | Inspiration | Should see 5-6 anterior ribs (or 9-10 posterior ribs) above the diaphragm. Poor inspiration makes the heart look bigger and the bases appear collapsed. |
| P | Projection | PA (posteroanterior) vs AP (anteroposterior). On AP films the scapulae project into the lung fields and the heart appears magnified - do NOT call cardiomegaly on an AP. Bedside films are almost always AP. |
| E | Exposure | Vertebral bodies should just be visible behind the cardiac shadow. Underexposed = everything looks white; overexposed = subtle opacities are hidden. |
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)
Compare both lungs systematically - divide each into upper, mid, and lower zones.
What to look for:
| Finding | Description | Common causes |
|---|---|---|
| Consolidation | Homogeneous opacity, air bronchograms present | Pneumonia, infarction, hemorrhage |
| Collapse/atelectasis | Lobar volume loss, fissure displacement, increased density | Endobronchial obstruction, mucus plug |
| Pneumothorax | Visible pleural line with no lung markings beyond it | Spontaneous, trauma, iatrogenic |
| Nodule/mass | Focal rounded opacity | Malignancy, granuloma, abscess |
| Interstitial pattern | Reticular, nodular, or ground-glass changes | Pulmonary edema (Kerley B lines), ILD, infection |
| Hyperinflation | Flat diaphragms, increased AP diameter, barrel chest appearance | COPD, asthma |
Silhouette sign: Loss of a normal border (e.g., right heart border lost with right middle lobe consolidation) tells you which lobe is affected.
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
Divide into:
- 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)
Always check position and document:
| Device | Correct position |
|---|---|
| ETT (endotracheal tube) | Tip 3-5 cm above carina, at level of T3-T4 |
| Central venous catheter | Tip at SVC/right atrial junction |
| NG tube | Tip below diaphragm, well into stomach |
| Chest drain | In pleural space, oriented toward the pathology |
| PICC line | Tip in SVC or upper right atrium |
Quick Reference: Common Patterns
| Pattern | Think of |
|---|---|
| Unilateral white-out | Large pleural effusion, total lung collapse, pneumonectomy |
| Bilateral basal airspace shadowing + Kerley B lines | Pulmonary edema (heart failure) |
| Upper lobe fibrosis + cavitation | TB, sarcoidosis, ankylosing spondylitis |
| Lower lobe fibrosis | IPF, asbestosis |
| Bat-wing/butterfly perihilar pattern | Pulmonary edema |
| Ring shadows / hyperinflation | Bronchiectasis, COPD |
| Air under diaphragm | Perforated viscus |
Practical Tips
- Always use the same sequence - it doesn't matter which order, but being consistent prevents you from skipping things.
- Compare sides - asymmetry is often the clue.
- Context is king - the same opacity can be pneumonia or malignancy depending on the patient.
- Look at the edges - apices, costophrenic angles, and behind the heart are common areas where abnormalities are missed.
- A normal CXR doesn't rule out serious pathology - a PA film misses around 20-25% of pulmonary nodules < 1 cm.
Sources: Harrison's Principles of Internal Medicine 22E (2025) | Grainger & Allison's Diagnostic Radiology | NCBI Bookshelf - A Systematic Approach to Chest Radiographic Analysis | GeekyMedics CXR Interpretation Guide
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