Radiographic Findings of Pneumothorax on Chest X-Ray
The key finding on chest X-ray for pneumothorax is the visualization of the visceral pleural line—a thin, sharply defined white line representing the edge of the collapsed lung, with absence of lung markings peripheral to this line 1.
Primary Radiographic Signs
Upright Chest X-Ray (Standard View)
- Visceral pleural line: The hallmark finding—appears as a thin, sharp, white line that follows the expected course of the lung margin 1, 2
- Increased lucency (darkness): The area beyond the pleural line appears blacker due to air in the pleural space with no lung tissue 1
- Absence of lung markings: No vascular or bronchial markings extend beyond the visceral pleural line 2
Supine Chest X-Ray (Common in Trauma/ICU Settings)
When patients are supine, air rises anteriorly, making pneumothorax harder to detect. Look for these alternative signs 3, 4:
- Deep sulcus sign: Abnormally deep and lucent costophrenic angle
- Double diaphragm sign: Two diaphragm-lung interfaces visible
- Increased lucency over upper abdomen: Unusually dark appearance over the upper quadrants
- Unusually sharp anterior diaphragmatic surface: Crisp definition of the hemidiaphragm 1
Important Clinical Caveats
Expiratory Films Are NOT Recommended
The BTS guidelines explicitly state that expiratory chest radiographs should not be used for routine diagnosis of pneumothorax 5. Standard inspiratory PA films are sufficient.
When Standard CXR Is Inadequate
Consider additional imaging when 5:
- Lateral or lateral decubitus views: If clinical suspicion is high but PA film is normal
- CT scanning: Gold standard for differentiating pneumothorax from complex bullous disease, detecting occult pneumothorax (which accounts for 52-63% of traumatic cases), or when surgical emphysema obscures the plain film 5, 3, 4
Common Pitfalls to Avoid
Skinfold artifacts can mimic pneumothorax but have distinguishing features 2, 6:
- Skinfolds appear as broad opacities (not thin lines)
- Have a lucent line laterally (Mach band effect)
- Do NOT follow the expected course of visceral pleura
- Lung markings project across the line (unlike true pneumothorax)
- When in doubt, repeat the film or obtain CT
Sensitivity Limitations
Supine portable CXR has poor sensitivity for pneumothorax, particularly small ones 3, 7. In trauma patients with chest tenderness or mechanism suggesting pneumothorax, consider:
- Oblique chest radiograph as a fast screening tool 3
- Low threshold for CT imaging in critically ill patients 4
- Ultrasound at easily accessible windows (anterior, apical, and basal locations where occult pneumothoraces commonly occur) 4
Size Assessment
While CXR can estimate pneumothorax size (measuring the rim of air from chest wall to lung edge), clinical history and physical examination are NOT reliable indicators of size 5. The 2023 BTS guidelines reference a "rim of air >2 cm" as a decision point for management 8, though CT remains more accurate for precise sizing 9.