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Normal Chest X-Ray (CXR) - Anatomy & Interpretation

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Standard Views

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Key Structures - What to See

1. Trachea

• Midline at the neck, deviates slightly to the right at the level of the aortic arch - a normal variant.
• The carina (bifurcation) lies at the level of T4/T5 (roughly the angle of Louis).
• The carinal angle is normally < 70°; widening suggests left atrial enlargement.

2. Heart

• The cardiothoracic ratio (CTR) should be < 0.5 on a PA film (heart width : widest chest width).
• Right heart border = right atrium.
• Left heart border (top to bottom) = aortic knuckle → pulmonary trunk → left atrial appendage → left ventricle.
• The right hemidiaphragm is normally higher than the left by ~15 mm (up to 30 mm is normal) because of the liver.

3. Mediastinum

• Superior mediastinum: contains aorta, SVC, trachea, oesophagus, lymph nodes.
• Aortic knuckle: visible on the left at the level of T4 - the aortic arch.
• Mediastinal widening (> 8 cm at T4) raises concern for aortic pathology, lymphoma, or mass.

4. Hila

• Left hilum is normally higher than the right by up to 3 cm.
• Hila are composed mainly of pulmonary arteries (upper lobe veins also contribute).
• Hilar enlargement may be unilateral (lymphoma, sarcoid, lung cancer) or bilateral (sarcoidosis, bilateral hilar lymphadenopathy).

5. Lungs

• Lung markings (vascular shadows) should be visible to the lung periphery.
• Upper zone vessels are normally smaller than lower zone vessels on an erect film.
• Upper lobe blood diversion (upper > lower lobe vessel size) = sign of raised pulmonary venous pressure.
• The fissures: horizontal fissure (right side, runs from hilum to 6th rib laterally); oblique fissures (not seen on PA, visible on lateral).

6. Diaphragm

• Each hemidiaphragm is a smooth, convex upward curve.
• The diaphragm normally lies at the level of the 5th or 6th anterior rib interspace in the mid-lung field.
• The costophrenic (CP) angles should be sharp and acute - blunting requires ~200-500 mL of pleural fluid.
• The cardiophrenic angles are often less well-defined due to adjacent fat.

7. Soft Tissues & Bones

• Check ribs (fractures, notching), clavicles, scapulae, spine.
• Rib notching (inferior) = coarctation of the aorta.
• Soft tissue: breast shadows, subcutaneous emphysema, neck/axillary masses.

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A Systematic Approach (ABCDE)

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Common Normal Variants (Not Pathology)

• Slight right tracheal deviation at the aortic arch
• Prominent aortic knuckle in the elderly (unfolded aorta)
• Visible azygos fissure (accessory fissure, right upper lobe)
• Slight leftward rotation making the left heart border appear more prominent
• Fat pads at cardiophrenic angles - can simulate cardiomegaly

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Judging Film Quality (RIPE)

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