Top 10 Classic X-Ray Findings with Images and Hallmarks

1. Air Bronchogram Sign

• Branching linear lucencies (air-filled bronchi) visible within an opacified/consolidated lung
• Confirms the opacity is intrapulmonary (not pleural or mediastinal)
• Seen when alveoli are fluid-filled but airways remain patent
• Generalized form = ARDS/hyaline membrane disease
• Also seen in: bronchoalveolar carcinoma, lymphoma, radiation fibrosis, sarcoidosis

2. Silhouette Sign

• Loss of a normally visible border between two structures of the same radiodensity (soft tissue + soft tissue = no visible margin)
• Right heart border lost = right middle lobe/right lingular pathology
• Left heart border lost = lingula or left lower lobe
• Diaphragm obscured = lower lobe consolidation or effusion
• Key teaching point: "You can only see a structure if something of different density is adjacent to it"
• Hilum overlay sign: subtype - used to localize hilar masses (if hilar vessels still visible through mass, it's anterior or posterior to hilum)

3. Pleural Effusion - Meniscus Sign

• Dependent opacity with a curved (meniscus-shaped) upper border - higher laterally, lower medially on PA view
• Blunting of costophrenic angles (need ~200-300 mL to blunt on PA; 50-75 mL on lateral)
• Ipsilateral diaphragm obscured (silhouette sign)
• Massive effusion: complete white-out of hemithorax + contralateral mediastinal shift
• Subpulmonic effusion: apparent elevation of hemidiaphragm; lateral decubitus view confirms

4. Pneumothorax + Deep Sulcus Sign

• Visible visceral pleural line with absent lung markings peripheral to it
• Ipsilateral hyperlucency
• Tension PTX: mediastinal shift away from affected side + ipsilateral diaphragmatic depression

• Unusually deep and lucent costophrenic angle - air collects anteriorly/basally in supine patient
• Etched diaphragm: hemidiaphragm appears sharper than contralateral side
• Etched mediastinum: increased contrast along heart border

5. Bat-Wing / Butterfly Pattern - Pulmonary Edema

• Bilateral opacities radiating outward from the hila in a fan/bat-wing shape - perihilar consolidation sparing the lung periphery
• Develops when pulmonary venous pressure exceeds 30 mmHg
• Associated with: cardiomegaly (CTR >0.5), Kerley B lines, upper lobe vascular diversion, pleural effusions
• Kerley B lines: short horizontal lines (1.5-2 cm) at the lung bases, perpendicular to pleura = interlobular septal thickening
• Kerley A lines: longer lines (5-10 cm) from hilum to periphery = deep septal fluid

6. Cardiomegaly (CTR >0.5)

• Cardiothoracic ratio (CTR) > 0.5 on a PA film (unreliable on AP/supine)
• Pericardial effusion gives a "flask-shaped" or globular cardiac silhouette
• Constrictive pericarditis: pericardial calcification (shell-like, best seen on lateral)
• Associated findings: upper lobe diversion, Kerley B lines, pleural effusions

7. Lobar Consolidation

• Homogeneous opacification of a lobe with air bronchograms and intact lobe volume (no collapse)
• Silhouette sign localizes the lobe affected
• Right lower lobe: posterior opacity, visible through cardiac shadow
• Left lower lobe: triangular opacity behind heart, "straight lateral border of heart," loss of left hemidiaphragm
• Klebsiella: "Bulging fissure sign" - fissure bulges convexly toward the opacity due to exudate volume

8. Hampton's Hump + Westermark Sign (Pulmonary Embolism)

• Wedge-shaped, pleura-based opacity with a rounded convex apex pointing toward the hilum
• Represents pulmonary infarction distal to the embolus
• Also called the "melting sign" - resolves over days like a melting ice cube
• Present in ~22% of angiographically confirmed PE (not sensitive)

• Focal oligemia/hyperlucency distal to an occluded pulmonary artery - decreased vascular markings
• Rare (~2% of PE cases); caused by obstruction + reflex vasoconstriction
• Fleischner sign (companion): prominent dilated central pulmonary artery due to large embolus or elevated pulmonary arterial pressure

9. Golden S Sign (Right Upper Lobe Collapse with Central Mass)

• The "S-shaped" curve formed at the minor fissure:
  • Lateral/superior concave portion = downward-displaced minor fissure (collapsed RUL)
  • Medial/inferior convex portion = the central hilar mass bulging outward
• Virtually pathognomonic for central obstructing carcinoma when RUL collapses
• Named by Golden in 1925

10. Pneumoperitoneum (Free Air Under Diaphragm)

• Crescent of free air visible beneath one or both hemidiaphragms on upright CXR (right side more common - liver creates contrast)
• Requires as little as 1 mL of free air detectable on erect CXR
• Rigler's sign (supine): both sides of bowel wall visible due to intraluminal + extraluminal air
• Falciform ligament sign (supine): free air outlines the falciform ligament as a vertical line
• Continuous diaphragm sign: air outlines inferior aspect of diaphragm including under the heart
• Key: upright film is most sensitive; lateral decubitus (left side down) is alternative

Quick Reference Table