Chest X-rays (CXRs) are among the most frequently ordered imaging investigations in clinical practice. For a radiology resident, becoming fluent in interpreting CXRs is non-negotiable. Beyond pattern recognition, certain classic radiological signs serve as diagnostic shortcuts—alerting you to specific conditions at a glance.
Here’s a resident-friendly guide to the most important chest X-ray signs you must know — for exams, viva prep, and on-call confidence.
🔍 1. Silhouette Sign
What it means:
Loss of normal borders between thoracic structures of different radiographic densities (usually air and soft tissue).
Where it helps:
-
Right heart border obscured → Right middle lobe consolidation
-
Left heart border obscured → Lingular consolidation
Remember:
Localization of lung pathology is often possible by understanding which structure's silhouette is lost.
🪶 2. Air Bronchogram Sign
What it means:
Air-filled bronchi are made visible by surrounding alveolar consolidation.
Seen in:
-
Pneumonia
-
Pulmonary edema
-
ARDS
-
Alveolar tumors (e.g., bronchoalveolar carcinoma)
Tip:
If air bronchograms are present, the lesion is likely intrapulmonary, not pleural.
🪞 3. Golden S Sign (Reverse S Sign of Golden)
What it means:
An S-shaped curve of the minor fissure due to upper lobe collapse with a central mass preventing complete fissure movement.
Seen in:
-
Right upper lobe collapse due to central bronchogenic carcinoma.
Remember:
Mass + lobar collapse → think malignancy until proven otherwise.
🌫 4. Bat Wing Appearance
What it means:
Bilateral, perihilar alveolar opacities resembling bat wings.
Classic for:
-
Pulmonary edema, especially of cardiogenic origin.
Other causes:
ARDS, alveolar hemorrhage, Pneumocystis pneumonia (PCP)
🫧 5. Deep Sulcus Sign
What it means:
An abnormally deep costophrenic angle on a supine film due to air collecting anteriorly.
Seen in:
-
Pneumothorax, especially in trauma patients on ventilators.
Remember:
Always suspect pneumothorax in sudden desaturation + trauma with a deep sulcus on supine film.
🌪 6. Hydropneumothorax (Straight Line Sign)
What it means:
A horizontal air-fluid level in the pleural space.
Seen in:
-
Trauma with lung laceration
-
Iatrogenic injury (central line, biopsy)
-
Ruptured hydatid cyst
Tip:
Unlike pleural effusion (which shows a meniscus), this has a flat horizontal line.
🛠 7. Rib Notching
What it means:
Indents on the inferior border of ribs due to enlarged intercostal arteries.
Seen in:
-
Coarctation of aorta
Other causes:
Neurofibromatosis, Blalock-Taussig shunt (post-op)
🦋 8. Figure of 3 Sign
What it means:
Pre- and post-stenotic dilatation with indentation at the site of coarctation.
Seen in:
-
Aortic coarctation
Remember:
Often seen in conjunction with rib notching.
💧 9. Meniscus Sign
What it means:
Curved upper border of a pleural effusion rising higher laterally than medially.
Classic for:
-
Free pleural effusion
Tip:
If there's a straight upper border, suspect loculated fluid or hydropneumothorax.
💨 10. Collapsed Lung Signs
Right Upper Lobe Collapse:
-
Elevation of horizontal fissure
-
Golden S sign (if mass is present)
Right Middle Lobe Collapse:
-
Silhouette of right heart border lost
-
Wedge-shaped opacity seen on lateral view
Left Upper Lobe Collapse:
-
Veil-like opacity over upper zone
-
Shift of trachea toward the left
Bonus Signs (Exam Favorites):
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Hampton’s Hump – Wedge-shaped opacity from pulmonary infarction (PE)
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Westermark Sign – Oligemia distal to PE
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Boot-shaped Heart – TOF (Tetralogy of Fallot)
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Snowman Sign – TAPVC (Total Anomalous Pulmonary Venous Connection)
Conclusion
Mastering CXR signs is like learning a language—start with the alphabet (basic signs) before forming sentences (differentials and diagnosis). During residency, seeing is believing, so correlate these signs with real cases on PACS. Repetition and clinical correlation are the keys to retention.
Pin this blog, revise regularly, and let these signs guide your eye like a pro!
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