Principles
X-rays: electromagnetic radiation, absorbed by dense tissues (bone = white), transmitted through air (black). PA (posterior-anterior): standard, heart size accurate. AP (anterior-posterior): portable, supine, heart appears larger. Lateral: complements PA. Exposure: too light (underexposed, whiteout), too dark (overexposed, blackout). Penetration: thoracic spine visible through heart. Rotation: clavicles symmetric, spinous processes midline. Inspiration: 9-10 posterior ribs, 5-6 anterior ribs visible.
Systematic Approach
ABCDE: Airway (trachea midline), Bones (clavicles, ribs, spine), Cardiac (heart size, contours), Diaphragm (costophrenic angles, position), Effusions/Everything else (soft tissue, lines, tubes). Compare to prior. Look for: pneumothorax (absent lung markings, pleural line), effusion (blunting costophrenic angle), consolidation (air bronchograms), cardiomegaly (heart >50% thoracic width on PA), pulmonary edema (batwing, Kerley B lines).
Common Findings
Chest: consolidation (pneumonia, white opacity, air bronchograms), atelectasis (volume loss, shifted structures), pneumothorax (dark, no lung markings, pleural line), pleural effusion (blunted costophrenic angle), CHF (cardiomegaly, pulmonary edema, Kerley B lines), COPD (hyperinflation, flat diaphragms), tension pneumothorax (tracheal shift, mediastinal shift). Abdomen: free air (perforation), bowel obstruction (dilated loops, air-fluid levels), ileus. Bones: fractures, dislocations. Tubes/lines: verify placement.
Important Notes
- On a good inspiratory PA chest X-ray: 9-10 posterior ribs and 5-6 anterior ribs should be visible above the diaphragm.
- Tension pneumothorax: tracheal deviation AWAY from the affected side, mediastinal shift — emergency, decompress before X-ray if clinically suspected.
Clinical Tips
- Consolidation with air bronchograms indicates pneumonia — the alveoli are filled with fluid, but the bronchi remain air-filled (dark).
- Cardiomegaly: heart width >50% of thoracic width on PA film — but on AP (portable) film, heart appears artificially larger.
Summary
X-ray interpretation uses ABCDE approach (Airway, Bones, Cardiac, Diaphragm, Effusions) with attention to technique (rotation, penetration, inspiration).
