From the Guidelines
Pneumothorax is characterized by increased radiolucency, not opacity, on chest X-rays due to the presence of air in the pleural space. This is because air enters the pleural space between the lung and chest wall, causing the lung to collapse. The air-filled pleural space lacks the normal tissue density of the lung, resulting in a darker appearance on radiographs compared to the adjacent normal lung tissue. You can identify a pneumothorax by looking for a sharp lung edge with absence of lung markings beyond this edge, and sometimes a visible visceral pleural line. The collapsed lung itself may appear more opaque (whiter) due to atelectasis, but the pneumothorax space itself is radiolucent.
According to the BTS guidelines for the management of spontaneous pneumothorax 1, primary pneumothoraces arise in otherwise healthy people without any lung disease, and secondary pneumothoraces arise in subjects with underlying lung disease. The guidelines highlight the importance of subpleural blebs and bullae in the pathogenesis of primary pneumothorax, which are found in up to 90% of cases at thoracoscopy or thoracotomy and in up to 80% of cases on CT scanning of the thorax.
Key features to look for in diagnosing pneumothorax include:
- A sharp lung edge with absence of lung markings beyond this edge
- A visible visceral pleural line
- Increased radiolucency (darkness) in the affected area
- The collapsed lung may appear more opaque (whiter) due to atelectasis. Understanding this radiographic appearance is crucial for prompt diagnosis and management of pneumothorax, which may require interventions ranging from observation to chest tube placement depending on the size and symptoms, as described in the guidelines 1.
From the Research
Causes of Opacity in Pneumothorax
- Opacity in pneumothorax can be caused by various factors, including the presence of air or fluid in the pleural space, which can be detected using imaging modalities such as chest radiographs or computed tomography (CT) scans 2, 3, 4.
- The visceral pleura, a thin layer of tissue that surrounds the lungs, can also cause opacity in pneumothorax, and its disruption can lead to air leaks and persistent pneumothorax 2.
- Skinfold artifacts can also mimic the appearance of pneumothorax on radiographs, but can be differentiated by careful analysis of the characteristics of the linear shadow and its course 5.
Imaging Modalities for Diagnosing Pneumothorax
- Chest radiographs are commonly used to diagnose pneumothorax, but may not always detect small or occult pneumothoraces 3, 4.
- CT scans are more sensitive than chest radiographs and can detect smaller pneumothoraces, as well as other complications such as bronchopleural fistulas or oesophageal-pleural fistulas 2, 4.
- Ultrasound can also be used to diagnose pneumothorax, particularly in emergency settings, and has been shown to have higher sensitivity than chest radiographs 3.
Clinical Significance of Pneumothorax
- Pneumothorax can be a life-threatening condition, particularly if left untreated or if complications such as tension pneumothorax occur 3, 4.
- The incidence and clinical significance of pneumothorax can vary depending on the underlying cause, such as trauma or iatrogenic injury, and the presence of other thoracic injuries 4.
- The development of pneumothorax after procedures such as CT-guided lung biopsy can also have clinical significance, and factors such as nodule-to-pleura distance and emphysema can increase the risk of pneumothorax and pulmonary hemorrhage 6.