On a frontal chest X-ray, the pathognomonic sign of pneumothorax characterized by a thin, sharply demarcated radiolucent line parallel to the chest wall, with absent lung markings beyond it, is called:

Explanation

## Radiographic Signs of Pneumothorax **Key Point:** The visceral pleural line (also called the lung edge sign or pleural line) is the most specific and pathognomonic radiographic finding of pneumothorax on chest X-ray. ### Anatomy of the Sign - Represents the **collapsed visceral pleura** of the lung - Appears as a **thin, sharply demarcated radiolucent line** parallel to the chest wall - **Absence of lung markings** (vessels, bronchi) beyond this line — the space is occupied by air only - Best visualized on **expiratory views** (collapse is more pronounced) ### Key Features | Feature | Details | |---------|----------| | **Appearance** | Thin, white linear opacity | | **Location** | Parallel to lateral chest wall, usually at lung apex | | **Associated finding** | Hyperlucency (blackness) of pneumothorax space | | **Sensitivity** | Increases with larger pneumothorax; may be subtle in small PTX | | **Best seen on** | Expiratory CXR, prone views, or CT | **High-Yield:** The visceral pleural line is the **gold standard** for diagnosing pneumothorax on plain radiography. Small pneumothoraces may be missed on inspiratory films — always request **expiratory views** when clinical suspicion is high. ### Secondary Signs (Less Specific) - **Hyperlucency** of the hemithorax - **Mediastinal shift** (tension pneumothorax) - **Tracheal deviation** (tension pneumothorax) - **Absent lung markings** in periphery **Clinical Pearl:** In a supine patient (ICU setting), pneumothorax may collect anteriorly and be **invisible on standard CXR**. Use **CT chest** or **portable lateral decubitus view** for confirmation.