A 26-year-old male patient was admitted to the emergency department with sudden thoracic and supraclavicular pain and dyspnoea while playing football. During the last week, the patient complained of non-productive cough and rhinorrhea. Cardiac necrosis markers were normal. Chest x-ray, supraclavicular ultrasound and thoracic CT were performed.
The chest radiography was first misinterpreted as normal and a supraclavicular ultrasound ordered because of supraclavicular pain.
Supraclavicular ultrasound showed subcutaneous emphysema (Fig. 1) and a CT was then performed showing pneumomediastinum (Fig. 2A), with the air extending to the supraclavicular region, to the retropharyngeal space and surrounding the carotid arteries and jugular veins bilaterally (Fig 2B).
Retrospectively, although it was subtle, the chest radiography showed multiple signs of pneumomediastinum which could have been detected earlier if a careful analysis had been made.
Bilateral subcutaneous emphysema in the supraclavicular region could be seen (Fig. 3A). In addition, in the mediastinum, detachment of the parietal pleura from the right lateral border of the trachea with air between these two structures could be seen (Fig. 3B). Air outlining the outer contour of the right and left bronchi, a finding known as "double bronchial wall sign", was also visible (Fig. 3B).
Pneumomediastinum represents the presence of air within the mediastinum, and can be divided in spontaneous and secondary (to trauma, oesophageal or tracheobronchial injury).
Mediastinal air may have an intrathoracic (trachea, bronchi, lung, oesophagus) or extrathoracic (peritoneum, head, neck) source.
The most common origin of spontaneous and traumatic pneumomediastinum is the lung, and the responsible pathophysiologic mechanism is the Macklin effect which consists of alveolar wall rupture due to elevated alveolar pressures, followed by peri-bronchovascular air dissection into the mediastinum. [1, 2].
The most common presentation of spontaneous pneumomediastinum (SM) is acute retrosternal chest pain. Dyspnoea and subcutaneous emphysema may also be present .
Chest radiography is the standard diagnostic procedure. There are multiple radiographic signs described, such as [1, 2]:
- Double bronchial wall sign: Air outlining bronchial walls.
- Continuous diaphragmatic sign: Air posterior to the pericardium.
- Subcutaneous emphysema.
- Thymic sail sign: In children the thymus may become elevated.
On the lateral chest radiograph:
- Pneumoprecardium: Air anterior to the heart.
- Ring around the artery sign: Air enclosing the pulmonary artery.
The distinction between SM and a secondary cause of pneumomediastinum such as esophageal or tracheobronchial rupture can not always be made clinically. Chest radiography should be carefully analysed, as the differentiation is imperative since the first resolves naturally, whereas the last two are often managed surgically .
The most common site of oesophageal tear is in the left postero-lateral wall of the distal oesophagus, which usually leads to mediastinal air lateral to the aorta and between the parietal pleura and the left hemidiaphragm (Naclerio’s V sign). Moreover, reactive left lower lobe pneumonitis and left pleural effusion may also be found. If needed, the diagnosis may be confirmed with an esophagogram with gastrografin or CT .
When tracheobronchial injury is suspected, tracheobronchial morphology should be carefully assessed. The fallen lung sign (collapsed lung away from the mediastinum), although rare, is pathognomonic of bronchial fracture .
The distinction between pneumomediastinum and pneumothorax is usually easily made by the air distribution. However, in the case of a medial pneumothorax, the diagnosis may be difficult, and a contralateral decubitus view may be needed to assess whether the air shifts laterally .
Pneumopericardium may be suspected when only the pericardial sac itself is visualized.
Spontaneous pneumomediastinum is usually a benign condition and treatment consists of rest, analgesia and oxygen administration. Prophylactic antibiotherapy has been recommended in order to prevent mediastinitis. Rarely malignant pneumomediastinum can develop, with elevated pressures impairing venous return to the heart .
Differential Diagnosis List