A 28-year-old male smoker presents to the emergency department with acute onset right-sided pleuritic chest pain and dyspnea of 2 hours duration. He denies trauma or recent procedures. On examination, breath sounds are diminished on the right side, and percussion note is hyperresonant. A chest X-ray (posteroanterior view) is obtained. Which radiological sign would be most specific for confirming the diagnosis of pneumothorax?

Explanation

## Diagnosis of Pneumothorax on Chest X-Ray **Key Point:** The visceral pleural line (pleural stripe) is the pathognomonic radiological sign of pneumothorax. It appears as a thin, sharp white line representing the collapsed visceral pleura, with absent lung markings (vessels, bronchi) in the area peripheral to this line. ### Radiological Signs of Pneumothorax | Sign | Description | Specificity | Notes | |------|-------------|-------------|-------| | **Visceral pleural line** | Thin white line marking the edge of collapsed lung | **Highest** | Pathognomonic; best seen on inspiration | | **Absent lung markings** | No vascular or bronchial markings beyond pleural line | High | Confirms air in pleural space | | Mediastinal shift | Shift away from pneumothorax | Moderate | Indicates tension pneumothorax (emergency) | | Costophrenic angle blunting | Suggests pleural effusion, not pneumothorax | Low | Opposite finding | | Homogeneous opacity | Suggests consolidation or atelectasis | Low | Not characteristic of simple pneumothorax | **High-Yield:** The pleural line must be distinguished from other linear opacities (skin folds, clothing artifacts). True pleural lines: - Are **curved** (follow the chest wall contour) - Have **no lung markings beyond** them - Are best seen on **full inspiration** - Persist on **serial radiographs** ### Secondary Signs Supporting Pneumothorax 1. **Lung edge sign:** Visible collapsed lung margin 2. **Deep sulcus sign:** Hyperlucency at the lung base on frontal view (especially in supine patients) 3. **Mediastinal shift:** Only in tension pneumothorax (hemodynamic compromise) 4. **Subcutaneous emphysema:** Air tracking into soft tissues (suggests ongoing air leak) **Clinical Pearl:** In a supine patient (ICU setting), the pneumothorax may not be visible on frontal radiograph because air rises anteriorly. Look for the **deep sulcus sign** (exaggerated lucency at the costophrenic angle) or obtain a lateral decubitus view. **Warning:** Do not confuse pneumothorax with: - ~~Skin folds~~ (do not follow pleural anatomy; visible on both sides of film) - ~~Bullae~~ (have lung markings within them; no sharp pleural line) - ~~Pneumomediastinum~~ (air in mediastinum, not pleural space) [cite:Felson's Principles of Chest Roentgenology Ch 10]