Pneumomediastinum

Disruption of parenchyma with interstitial dissection of air is the most common aetiology of pneumomediastinum due to blunt thoracic trauma. Pneumomediastinum is often asymptomatic, but it may cause chest pain or dyspnoea. It can lead to pneumothorax when the mediastinal pleura ruptures. In these circumstances, pneumomediastinum does not require any treatment. Rarely, it may cause hypotension by impairing venous return to the heart.

Radiographically pneumomediastinum is manifested by lucent streaks or bubbles of gas in the mediastinal soft tissues, that outline mediastinal structures, elevate the mediastinal pleura and often extend into the neck or chest wall (Fig.1 a). Mediastinal air between the heart and the superior surface of the diaphragm results in "continuous diaphragm sign" on the frontal chest radiograph and "continuous left hemidiaphragm sign" on the lateral view. Nacleiros V sign refers to gas outlining the lateral margin of descending aorta and extending laterally between the parietal pleura and medial hemidiaphragm. The ring around the artery sign is formed by gas surrounding the extrapericardial portion of the right main pulmonary artery. Pneumomediastinum can dissect along the parietal pleura and extend into the extrapleural tissues and create linear or round lucent gas collections, known as the extrapleural air sign. In some cases pneumomediastinum can be confused with pneumothorax or pneumopericardium, but analysis of the distribution of the gas and accompanying signs will usually distinguish these conditions. Because gas in pneumomediastinum, unlike in pneumothorax and pneumopericardium, does not change in distribution with change in patient position, a contralateral decubitus view can be obtained to determine whether the gas shifts or not. CT demonstrates streaks of air in the mediastinum (Fig.1 b), and, more importantly, other associated mediastinal, pleuroparenchymal and chest wall abnormalities.

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