## Radiological Signs of Pneumothorax **Key Point:** The visceral pleural line (lung edge) with absent lung markings beyond it is the pathognomonic sign of pneumothorax on chest X-ray. This represents the collapsed lung margin separated from the chest wall by air. ### Frontal (PA/AP) Radiograph Findings | Finding | Sensitivity | Specificity | Notes | |---------|-------------|-------------|-------| | Visceral pleural line | High | Very high (pathognomonic) | Curved line parallel to chest wall; no vessels beyond | | Mediastinal shift | Low-medium | Medium | Only in tension pneumothorax | | Tracheal deviation | Low | Low | Non-specific; occurs in many conditions | | Hyperinflation contralateral | Low | Low | Occurs in obstructive diseases | **High-Yield:** The visceral pleural line is best seen at the lung apex and along the lateral chest wall. Small pneumothoraces (<2 cm) may be missed on standard frontal views and require: - Expiratory films (collapse increases relative air volume) - Lateral decubitus views (air rises, becomes more visible) - CT chest (gold standard for small PTX) **Clinical Pearl:** In a supine patient (ICU), pneumothorax air rises anteriorly and may only be visible as a deep sulcus sign (hyperlucency at lung base) or anterior pneumomediastinum on CT. **Mnemonic: VPL** — **V**isceral **P**leural **L**ine = the diagnostic finding. [cite:Felson's Principles of Chest Roentgenology] 
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