A 28-year-old male presents to the emergency department with acute onset right-sided chest pain and dyspnea after a fall from a motorcycle 2 hours ago. Vital signs: HR 110/min, BP 128/82 mmHg, RR 24/min, SpO₂ 94% on room air. Physical examination reveals decreased breath sounds on the right side with hyperresonance to percussion. A chest X-ray (PA view) is obtained. Which radiological sign, if present on the CXR, would be most specific for pneumothorax?

Explanation

## Radiological Signs of Pneumothorax **Key Point:** The **visceral pleural line** (also called the lung edge or pleural stripe) is the most specific radiological sign of pneumothorax. It appears as a thin, sharply demarcated radiopaque line that represents the collapsed lung edge, with air (black) visible between this line and the chest wall. ### Pathophysiology of the Pleural Line When air enters the pleural space, the lung collapses inward. The visceral pleura (which clings to the lung surface) becomes visible on X-ray because: 1. Air in the pleural space (radiolucent) contrasts with the visceral pleura (radiopaque) 2. The normal lung parenchyma beyond the pleural line is absent (only air remains) 3. This creates a sharp, linear boundary ### High-Yield Radiological Signs of Pneumothorax | Sign | Description | Specificity | Notes | |------|-------------|-------------|-------| | **Visceral pleural line** | Thin radiopaque line = lung edge | **Most specific** | Diagnostic gold standard on CXR | | Lung edge sign | Same as above | Very high | Pathognomonic when present | | Absent lung markings | No vascular markings beyond pleural line | High | Confirms air-filled pleural space | | Hyperlucency | Increased radiolucency of hemithorax | Moderate | Non-specific; can occur with bullae, COPD | | Mediastinal shift | Shift away from affected side | Indicates tension PTX | Sign of hemodynamic compromise | | Deep sulcus sign | Deepened costophrenic angle on frontal CXR | Moderate | More sensitive in supine patients | **Clinical Pearl:** On a supine CXR (common in trauma), the **deep sulcus sign** (hyperlucency in the anteromedial lung base) may be more apparent than the pleural line. However, on an upright PA view (as in this case), the **visceral pleural line** is the gold standard. **High-Yield:** The pleural line is typically: - Located 1–3 cm from the chest wall (small PTX) or >3 cm (large PTX) - Best seen on the lateral aspect of the hemithorax - Accompanied by absence of lung markings (vessels, bronchi) between the line and the chest wall ### Why This Patient's Presentation Fits - Acute trauma (fall) → risk of traumatic pneumothorax - Decreased breath sounds + hyperresonance → physical signs of PTX - Upright CXR → pleural line most visible - PA view → optimal for detecting pleural line **Tip:** Always scan the **lateral lung fields** on CXR when pneumothorax is suspected—the pleural line is easiest to spot there.