Table of contents · 7 sections
Chest X-ray (CXR) is the most common diagnostic imaging procedure in the world. Every physician must be able to systematically evaluate a chest radiograph and identify main pathological patterns. This article provides a step-by-step analysis algorithm, normal radiographic anatomy, and key pathologies.
Technique and Projections
| Parameter | Standard Radiography |
|---|---|
| Projection | Posteroanterior (PA) view — standard. Lateral view — supplementary |
| Respiration | Deep inspiration (≥10 posterior ribs visible) |
| Distance | 180 cm (PA) — minimizes cardiac silhouette magnification |
| AP projection | In supine patients — heart appears enlarged (closer to the film), mediastinum widened |
Systematic Approach to Analysis (ABCDE)
The ABCDE mnemonic ensures consistency and completeness:
- A — Airway: trachea midline? Deviation → pneumothorax (away from the lesion), atelectasis (toward the lesion), mediastinal mass
- B — Bones: ribs (fractures, lytic lesions), spine, clavicles, scapulae
- C — Cardiac: cardiothoracic ratio (CTR) <50% in PA. Enlargement → cardiomegaly. Chamber contours
- D — Diaphragm: right hemidiaphragm 1–2 cm higher than the left (liver). Free air under the diaphragm → perforation! Costophrenic angles (sinuses) — must be sharp
- E — Effusions/Everything else: pleural effusion (blunting of the sinus, Damoiseau meniscus), soft tissues (subcutaneous emphysema, mastectomy)
And further — lung fields: compare symmetrical zones, look for opacities, lucencies, nodules.
Normal X-ray Anatomy
| Structure | Normal Findings |
|---|---|
| Lung Hila | Left hilum is higher than the right (left pulmonary artery arches over the left main bronchus). Structured, without enlargement |
| Mediastinum | Expansion ≤8 cm. Aortic «nipple» on the left |
| Pulmonary pattern | Visible to the periphery, tapering toward the edges. Vascular genesis |
| Pleural sinuses | Sharp (free). Blunting → effusion ≥200–300 ml |
| Heart | CTR <50%. Right contour — RA, left — LV + aortic arch |
Main pathological patterns
| Pattern | Description | Causes |
|---|---|---|
| Consolidation (opacity) | Homogeneous opacity with air bronchogram | Pneumonia (lobar), pulmonary edema |
| Atelectasis | Opacity + mediastinal shift TOWARD the lesion + elevated diaphragm dome | Bronchial obstruction (tumor, mucus), compression |
| Pleural effusion | Homogeneous opacity at the base, Damoiseau's meniscus, mediastinal shift AWAY from the lesion (with large volume) | Transudate (CHF, cirrhosis), exudate (pneumonia, cancer, TB) |
| Pneumothorax | Radiolucency without pulmonary pattern + visible lung margin | Spontaneous (young, tall), traumatic, iatrogenic |
| Interstitial changes | Reticularity (reticular pattern), Kerley lines (B-lines) | Pulmonary edema, fibrosis, lymphangitis |
| Solitary pulmonary nodule | Rounded shadow <3 cm in diameter | Benign (granuloma, hamartoma) vs malignant (cancer) |
Radiological signs of heart failure
Mnemonic ABCDE (alternative):
- Alveolar oedema — "bat-wing" opacification (peripheral oedema)
- B (Kerley B lines) — horizontal lines at the periphery of the lower lobes (interstitial oedema)
- Cardiomegaly — CTR >50%
- Diversion (pulmonary blood flow redistribution) — upper lobe vessel dilatation (normally lower lobe vessels are wider)
- Effusion — pleural effusion (most commonly right-sided or bilateral)
Radiological Emergencies
- Tension pneumothorax — mediastinal shift AWAY from the affected side, diaphragmatic flattening → emergency decompression (needle in the 2nd intercostal space)
- Free gas under the diaphragm → hollow viscus perforation → emergency surgery
- Mediastinal widening + history of trauma → aortic rupture → emergency CT angiography
- Foreign body — radiopaque (metal, bone), unilateral ventilation impairment
Frequently asked questions
How to differentiate atelectasis from pleural effusion?
Both cause opacification, but: atelectasis — mediastinum shifts TOWARDS the affected side (volume loss), elevated diaphragmatic dome. Effusion — mediastinum shifts AWAY from the side (volume increase), Damoiseau's meniscus. In lateral decubitus (lying on the affected side), effusion fluid shifts along the chest wall.
Why shouldn't the cardiothoracic ratio (CTR) be assessed on an AP chest X-ray?
In the AP projection (supine), the heart is closer to the X-ray tube and farther from the detector → its shadow is magnified (magnification effect). The CTR is falsely elevated. The standard is the PA projection (standing), where the heart is closer to the detector. If the patient cannot stand, interpret with caution.
Study radiology through interactive lessons on the platform. Related topics: pneumonia, ECG, acute abdomen. Use clinical calculators for radiological scoring systems.