Chest X-Ray | CXR Interpretation Guide & Imaging Diagnosis

Systematic Approach to CXR Interpretation

Follow the ABCDE-FGHI mnemonic for comprehensive evaluation.

Airway & Adequacy

Trachea — midline or deviated?
Carina — bifurcation at T4-T5
Main bronchi visible
Rotation: spinous processes equidistant from clavicle heads
Inspiration: 5-7 anterior ribs or 9-10 posterior ribs visible
Exposure: vertebral bodies just visible behind heart

Bones & Soft Tissues

Ribs: fractures, lytic/sclerotic lesions
Clavicles: symmetry, fractures
Spine: alignment, vertebral body height
Scapulae: projected out in PA film
Soft tissues: subcutaneous emphysema, masses
Breast shadows: mastectomy signs

Cardiac Silhouette

Cardiothoracic ratio < 0.5 on PA film
Right heart border: RA + SVC
Left heart border: aortic knob, PA, LAA, LV
Boot-shaped (RVH), globular (pericardial effusion)
Retrocardiac space (lateral view)
Valvular calcifications

Diaphragm

Right hemidiaphragm ~1-2 cm higher than left
Smooth dome shape
Costophrenic angles: sharp (blunting = effusion ~200ml)
Free gas under diaphragm (pneumoperitoneum)
Elevated hemidiaphragm: phrenic nerve palsy, subpulmonic effusion
Eventration vs paralysis

Effusion & Extra-thoracic

Pleural effusion: meniscus sign
Loculated vs free-flowing
Supine: veiling opacity over hemithorax
Lines & tubes: ETT, CVC, NG tube, chest drain
Pacemaker/ICD leads positioning
Surgical clips, sternal wires

Fields (Lung)

Compare zones: upper, mid, lower bilaterally
Opacities: consolidation, ground-glass, nodules
Lucency: pneumothorax, bullae, emphysema
Interstitial vs alveolar pattern
Pulmonary vasculature: upper lobe diversion
Hilum: size, density, position (left 2cm higher)

Technical Quality Assessment (RIPE)

R — Rotation

Spinous processes equidistant between medial clavicular ends

I — Inspiration

5-7 anterior ribs or 9-10 posterior ribs above diaphragm

P — Projection

PA preferred (scapulae rotated out); AP magnifies heart

E — Exposure

Lower thoracic vertebrae just visible behind cardiac silhouette

Normal CXR Anatomy

Key anatomical landmarks on a standard PA chest radiograph.

Mediastinal Structures

Superior mediastinum	Trachea, great vessels, esophagus, thoracic duct
Anterior mediastinum	Thymus (4 T's: Thymus, Teratoma, Thyroid, Terrible lymphoma)
Middle mediastinum	Heart, pericardium, great vessels, trachea bifurcation
Posterior mediastinum	Descending aorta, esophagus, vertebral bodies, neurogenic tumors

Hilum & Vasculature

Left hilum	~2 cm higher than right (left PA rides over left main bronchus)
Hilar density	Equal bilaterally; increased = lymphadenopathy/mass
Normal vasculature	Lower lobe vessels > upper lobe (gravity-dependent)
Upper lobe diversion	Indicates pulmonary venous hypertension (>10 mmHg wedge)

Lung Zones

Upper zone	Above 2nd anterior rib (TB, sarcoidosis apical predominance)
Mid zone	Between 2nd and 4th anterior ribs
Lower zone	Below 4th anterior rib (aspiration, basal fibrosis)
Fissures	Horizontal (right only at 4th rib); oblique (bilateral)

Normal Measurements

CTR	< 50% on PA (< 60% on AP is unreliable)
Tracheal width	~2 cm (adult)
Aortic knob	< 4 cm width; unfolded in elderly
PA diameter	< 29 mm (pulmonary hypertension if enlarged)

Pathological Findings & Differential Diagnoses

Major radiological findings with clinical significance.

Consolidation (Air-Space Opacification)

Radiological Features

• Homogeneous opacification
• Air bronchograms (pathognomonic)
• Silhouette sign (loss of border)
• No volume loss (unlike atelectasis)
• Lobar or segmental distribution

Differential Diagnosis

• Infectious: Bacterial pneumonia, TB, fungal
• Non-infectious: Pulmonary edema, hemorrhage
• Neoplastic: Bronchoalveolar carcinoma, lymphoma
• Other: Organizing pneumonia (COP), eosinophilic pneumonia

Clinical Pearl: Silhouette sign localizes pathology — right heart border loss = RML; left heart border loss = lingula; left hemidiaphragm loss = LLL.

Pneumothorax

Radiological Features

• Visible visceral pleural line
• Absent lung markings beyond pleural edge
• Best seen at apex on erect film
• Deep sulcus sign (supine film)
• Tension: mediastinal shift AWAY, flattened diaphragm

Classification & Management

• Small: < 2cm at hilum level → observe
• Large: > 2cm → aspiration or chest drain
• Tension: Emergency needle decompression (2nd ICS MCL)
• Causes: Trauma, iatrogenic, spontaneous (tall thin males), COPD

⚠️ Emergency: Tension pneumothorax is a CLINICAL diagnosis. Do not delay treatment for imaging. Signs: tracheal deviation, absent breath sounds, hypotension, distended neck veins.

Pleural Effusion

Radiological Features

• Blunting of costophrenic angle (~200ml minimum)
• Meniscus sign (concave upper margin)
• Complete whiteout with mediastinal shift = massive
• Supine: hazy opacification, apical cap
• Lateral decubitus confirms free-flowing

Differential by Light's Criteria

• Transudative: CCF, cirrhosis, nephrotic syndrome, hypoalbuminemia
• Exudative: Infection (parapneumonic/empyema), malignancy, TB, PE
• Hemorrhagic: Trauma, malignancy, PE
• Chylous: Thoracic duct injury, lymphoma

Cardiomegaly & Heart Failure

Cardiomegaly Signs

• CTR > 50% on PA film
• Chamber-specific enlargement patterns
• LA: double density, splayed carina (>90°), posterior displacement on lateral
• LV: elongated apex below diaphragm
• RV: boot-shaped heart, filling retrosternal space

Heart Failure — ABCDE

• Alveolar edema (bat-wing/butterfly pattern)
• B lines (Kerley B — septal lines at bases)
• Cardiomegaly
• Diversion (upper lobe pulmonary venous)
• Effusion (bilateral pleural, often R > L)

Pulmonary Nodule / Mass

Nodule vs Mass

• Nodule: ≤ 3 cm; Mass: > 3 cm
• Solitary vs multiple
• Margins: spiculated (malignant) vs smooth (benign)
• Calcification: popcorn (hamartoma), central (granuloma)
• Cavitation: thick wall (malignant), thin wall (abscess, Wegener's)

Differential Diagnosis

• Malignant: Primary lung Ca, metastases (cannonball)
• Benign: Hamartoma, granuloma, AVM
• Infectious: Abscess, fungal ball (mycetoma), hydatid cyst
• Multiple: Metastases, septic emboli, Wegener's, rheumatoid nodules

Fleischner Criteria: Solitary pulmonary nodules 6-8mm in low-risk patients: follow-up CT at 6-12 months. > 8mm: consider PET-CT or biopsy.

Atelectasis (Collapse)

Key Signs (Volume Loss)

• Displacement of fissures TOWARD opacity
• Mediastinal shift toward affected side
• Elevated hemidiaphragm
• Crowding of ribs
• Compensatory hyperinflation of adjacent lobes

Types

• Resorptive: Bronchial obstruction (tumor, mucus plug)
• Compressive: Pleural effusion, pneumothorax
• Passive: Loss of surfactant (ARDS)
• Cicatricial: Fibrosis, TB scarring

Miliary Pattern

Features

• Innumerable tiny (1-3mm) nodules
• Uniform size and diffuse distribution
• "Snowstorm" appearance
• All zones affected uniformly

Differential

• Miliary TB (most common)
• Miliary metastases (thyroid, renal)
• Sarcoidosis
• Pneumoconiosis (silicosis, coal workers)
• Fungal: Histoplasmosis, Coccidioidomycosis

Classic Radiological Signs & Patterns

Eponymous signs and characteristic patterns in chest radiography.

Silhouette Sign

Felson's Sign

Loss of normal silhouette when adjacent structures have same density. Localizes pathology: lost R heart border = RML; lost L heart border = lingula; lost diaphragm = lower lobe.

Air Bronchogram

Consolidation Marker

Air-filled bronchi visible within opacified lung parenchyma. Indicates alveolar (air-space) filling. Present in pneumonia, pulmonary edema, ARDS. Absent in pleural effusion and atelectasis from obstruction.

Deep Sulcus Sign

Supine Pneumothorax

Abnormally deep costophrenic angle on supine film. Air collects anteriorly and basally in supine position. Critical for ICU patients who cannot sit upright.

Sail Sign

Thymic Shadow / Pericardial Effusion

Triangular opacity: In children = normal thymus; In adults = pericardial fat pad or large pericardial effusion giving "water bottle" configuration.

Golden S Sign

Central Mass with Collapse

Reversed S-shape of minor fissure in RUL collapse. Convex component = hilar mass (typically bronchogenic carcinoma). Concave component = collapsed distal lobe.

Hampton's Hump

Pulmonary Embolism

Wedge-shaped, pleural-based opacity representing pulmonary infarction. Apex points toward hilum. Seen in ~30% of PE cases with infarction.

Westermark Sign

Pulmonary Embolism

Focal oligemia (reduced vascularity) distal to the occluded vessel in PE. Area of increased lucency. Low sensitivity but high specificity.

Kerley B Lines

Interstitial Edema

Short (1-2cm) horizontal lines at lung periphery perpendicular to pleura. Represent thickened interlobular septa. Seen in early CCF, lymphangitis carcinomatosa.

Bat-Wing Pattern

Pulmonary Edema

Bilateral perihilar alveolar opacification sparing periphery. Classic in acute cardiogenic pulmonary edema. Also: uremic lung, Pneumocystis pneumonia.

Air Crescent Sign

Mycetoma / Aspergilloma

Crescent of air between a mass and the cavity wall. Classic for aspergilloma (fungal ball) within pre-existing cavity. Moves with position change.

Eggshell Calcification

Silicosis / Sarcoidosis

Peripheral ring-like calcification in hilar/mediastinal lymph nodes. Most commonly silicosis. Also sarcoidosis, post-radiation, Hodgkin's lymphoma (treated).

Continuous Diaphragm Sign

Pneumomediastinum

Visualization of the entire diaphragm from one lateral chest wall to the other, due to air outlining the inferior heart border. Indicates pneumomediastinum.

Structured Reporting Checklist

Comprehensive framework for generating a systematic CXR report.

Standard Report Structure

1. Clinical Information

Patient demographics, indication, comparison studies

2. Technical Factors

Projection (PA/AP), rotation, inspiration, exposure adequacy

3. Findings

Systematic description: airway, lungs, pleura, heart, mediastinum, bones

4. Lines & Devices

ETT (2-4cm above carina), CVC (SVC/RA junction), chest drains, NG tube

5. Impression

Summary diagnosis with differential, urgency level, recommendation

Quick Review Checklist

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Lines & Tubes — Ideal Positioning

ETT (Endotracheal)

• Tip 2-4 cm above carina
• Midline, not in right main bronchus
• Carina at T4-T5

Central Venous Catheter

• Tip at SVC/RA junction (T6-T7)
• Parallel to vessel wall
• Not in right atrium

Nasogastric Tube

• Bisects carina (midline)
• Below left hemidiaphragm
• Tip in stomach (not bronchus!)

Chest Drain

• Pneumothorax: apex directed
• Effusion: base directed
• All holes within thorax

Critical / Urgent Findings — Require Immediate Communication

Tension pneumothorax

Massive pleural effusion with mediastinal shift

Widened mediastinum (aortic dissection/rupture)

Free air under diaphragm (perforated viscus)

Malpositioned ETT / lines

New large pulmonary mass with bone destruction

Acute pulmonary edema (flash)

Rib fractures with flail segment

Foreign body in airway