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Complete Guide to Reading a Chest X-Ray

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1. Projections and Technical Quality

Standard Projections

• PA (Posteroanterior): The standard view. Patient stands with chest against the detector, X-ray beam enters from behind. The heart appears its true size because it is close to the detector.
• AP (Anteroposterior): Used for portable/bedside films. The heart appears magnified (~15-20% larger) because it is farther from the detector.
• Lateral: Obtained at 90° to the PA. Helps localize lesions to anterior or posterior segments and assess the retrosternal and retrocardiac spaces.

Assessing Technical Quality (RIPE mnemonic)

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2. Systematic Approach - "ABCDE"

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3. Airways

Trachea

• Midline or slightly right-deviated at the carina (normal, due to aortic arch).
• The right paratracheal stripe is a thin (≤5 mm) stripe visible in ~two-thirds of normals, formed by the tracheal wall and adjacent mediastinal fat. Widening suggests paratracheal lymphadenopathy or mass.
• The carina angle (subcarinal angle) is normally less than 70°. Widening suggests left atrial enlargement or subcarinal lymphadenopathy.

Bronchi

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4. Bones and Soft Tissues

Ribs

• Count ribs systematically: anterior ribs slope downward; posterior ribs are more horizontal.
• Look for fractures (including posterior rib fractures, which are harder to see than anterior ones).
• Lytic rib lesions (metastases, myeloma), sclerotic lesions, periosteal reaction.
• Key patterns:
  • Lytic lesion + anterior chest wall + chondroid calcification = chondrosarcoma
  • Expansile rib lesion in young patient = Ewing sarcoma or aneurysmal bone cyst
  • Posterior rib "ground-glass matrix" lesion = fibrous dysplasia
  • Multiple multifocal lytic lesions = myeloma or metastases

Clavicles and Sternum

• Erosion of the distal clavicle: rheumatoid arthritis, hyperparathyroidism.
• Sternal fractures are often not visible on PA film - lateral view or CT needed.

Soft Tissues

• Check for subcutaneous emphysema (linear lucencies tracking along tissue planes).
• Breast shadows (look for asymmetry suggesting mastectomy or mass).
• Skin folds from positioning can mimic pneumothorax.
• Fat pads at the cardiophrenic angles can simulate cardiomegaly if film is underexposed.

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5. Cardiac Silhouette and Mediastinum

Cardiac Size

• On a PA film: measure the cardiothoracic ratio (CTR). Normal is ≤0.5 (heart width < half the widest thoracic diameter at the same level as the widest cardiac point).
• On an AP film the heart always appears larger - CTR is unreliable.
• Cardiomegaly (CTR >0.5) suggests: left ventricular dilation (heart failure, dilated cardiomyopathy, valvular disease), pericardial effusion, or right heart enlargement.

Cardiac Borders

Mediastinal Contours and Stripes

• Right paratracheal stripe: ≤5 mm. Widening = lymphadenopathy, goiter, vascular anomaly.
• Azygos vein: Visible in the right tracheobronchial angle; ≤10 mm diameter is normal. Enlarges with raised central venous pressure (heart failure, IVC obstruction).
• Aortic knuckle: The aortic arch knob is normally visible left of the trachea. Unfolding/widening = hypertension, aneurysm. Absent/indistinct = acute aortic dissection (emergency).
• Left paraspinal line: Follows the thoracic spine. Widening or displacement = paraspinal abscess, hematoma (aortic pathology), mass.

Mediastinal Widening

• Aortic aneurysm/dissection
• Superior mediastinal mass (thyroid, thymoma, lymphoma, teratoma)
• Mediastinal hematoma after trauma
• Lymphadenopathy (TB, sarcoidosis, lymphoma, metastases)

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6. Diaphragm

• The right hemidiaphragm is normally higher than the left by ~15 mm (up to 30 mm is normal).
• Both hemidiaphragms are normally smooth convex domes, with their midpoint at the level of the 5th-6th anterior rib interspace.
• The lateral costophrenic angle is a sharp acute angle - blunting indicates pleural fluid (at least 200-500 mL needed to blunt the lateral angle; posterior CP angle blunts first with smaller effusions).

Diaphragm Abnormalities

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7. Pleura

Pleural Effusion

• Small amounts of free fluid initially collect under the lower lobes (subpulmonary position) and may be invisible on erect PA film.
• As volume increases:
  • ~200-500 mL: blunting of the posterior then lateral costophrenic angle
  • ~1000 mL: the opacity reaches the 4th anterior rib; classic concave (meniscus) upper margin, higher laterally
  • Massive effusion: opacification of the entire hemithorax with contralateral mediastinal shift

• Pleural effusion (massive)
• Consolidation (lobar pneumonia)
• Collapse
• Fibrothorax
• Combination (e.g., effusion + collapse)

Pneumothorax

• Visible as a sharp white pleural line with absent lung markings peripheral to it.
• Best seen in the apex on erect PA film. If suspected but not seen, obtain an expiratory film (accentuates the contrast) or lateral decubitus.
• On supine AP films (ICU), air collects anteriorly and inferiorly - look for the "deep sulcus sign" (abnormally deep lateral costophrenic angle).
• Tension pneumothorax: contralateral mediastinal shift, ipsilateral diaphragm depression - a clinical/radiological emergency.

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8. Lung Fields and Hila

Normal Lung Markings

• Lung markings (pulmonary vessels) taper toward the periphery.
• In the erect position, vessels in the lower zones are larger than those in the upper zones (gravity-dependent blood flow).
• Upper lobe blood diversion: vessels in the upper zones appear equal to or larger than lower zone vessels - indicates raised left atrial pressure (pulmonary venous hypertension, early heart failure).

Opacification Patterns

Consolidation

• Air space opacification with air bronchograms (air-filled bronchi visible as dark tubes within the opacity).
• Typically lobar or segmental, with preserved lung volume (unlike collapse).
• Causes: pneumonia, pulmonary edema (butterfly/bat wing pattern centrally), pulmonary hemorrhage, lung contusion.

Lobar Collapse (Atelectasis)

Ground-Glass Opacification (GGO)

• Hazy increased lung density without obliteration of vascular markings (unlike consolidation).
• On HRCT it is characteristic of early interstitial disease, alveolar edema, viral pneumonitis (COVID-19), drug reactions.

Interstitial Patterns

The Hila

• The left hilum is normally 0.5-1.5 cm higher than the right.
• Normal hilar shadows are formed by the pulmonary arteries and upper pulmonary veins.
• The right pulmonary artery lies anterior to the bronchi; the left pulmonary artery arches over the left main bronchus.
• Hilar enlargement: bilateral = sarcoidosis, lymphoma, bilateral hilar lymphadenopathy (BHL); unilateral = lymph node enlargement, pulmonary artery enlargement (proximal PE or pulmonary hypertension).
• Hilar displacement: upward = upper lobe collapse; downward = lower lobe collapse.

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9. Lines, Tubes, and Devices

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10. Common Abnormalities - Quick Reference

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11. Chest X-Ray in Trauma

• Pneumothorax (sensitivity ~50-80% vs. ~92% for ultrasound)
• Hemothorax
• Aortic/great vessel injury (mediastinal widening, obliterated aortic knuckle, tracheal deviation)
• Multiple rib fractures
• Sternal fracture (requires lateral view)
• Diaphragmatic rupture
• Pulmonary contusions

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12. HRCT Correlation

• Interstitial lung disease (fibrosis, EAA, sarcoidosis)
• Characterization of pulmonary nodules (volumetric assessment ≥0.6 mm)
• Pulmonary embolism (CTPA)
• Suspected bronchiectasis
• Diffuse alveolar processes

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Summary: A Systematic CXR Report Template

1. TECHNICAL QUALITY: PA/AP, rotation (symmetric clavicles?), 
   inspiration (posterior ribs visible?), exposure (vertebrae 
   through heart?)

2. AIRWAYS: Trachea midline? Carina angle? Paratracheal stripe?

3. BONES/SOFT TISSUES: Rib fractures? Lytic/sclerotic lesions? 
   Soft tissue abnormality?

4. CARDIAC: Size (CTR), borders, mediastinum width, aortic knuckle

5. DIAPHRAGM: Level (5th-6th AIS), symmetry, costophrenic angles 
   (sharp or blunted?)

6. PLEURA: Effusion? Pneumothorax? Pleural thickening?

7. LUNG FIELDS: Consolidation, collapse (silhouette signs), 
   nodules, masses, interstitial pattern

8. HILA: Left higher than right? Enlarged? Displaced?

9. DEVICES: ETT, CVC, NGT, drain positions correct?

10. EXTRAS: Sub-diaphragmatic air, surgical clips, foreign bodies

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