Differential diagnosis includes inflammatory conditions
The differential diagnosis for pneumomediastinum includes pericarditis, mediastinitis, Boerhaave syndrome, and acute coronary syndrome.
Pericarditis. In a patient with inflammation of the pericardium, you would hear reduced heart sounds and observe electrocardiogram (EKG) changes (eg, diffuse ST elevation in acute pericarditis). These signs typically would not be present in a patient with pneumomediastinum.1
Mediastinitis. Patients with mediastinitis—inflammation of the mediastinum—are more likely to have hypotension and shock.1
Boerhaave syndrome, or spontaneous esophageal perforation, has a similar presentation to pneumomediastinum but is more likely to be accompanied by hypotension and shock. Additionally, there would be extravasation of the contrast agent during swallow studies.2
Acute coronary syndrome is also part of the differential. However, in ACS, you would see ST changes on the patient’s EKG and elevated cardiac enzymes.1
Lateral x-rays are especially useful in making the diagnosis
Diagnosis is made by CXR and/or chest CT. On a CXR, retrosternal air is best seen in the lateral projection. Small amounts of air can appear as linear lucencies outlining mediastinal contours. This air can be seen under the skin, surrounding the pericardium, around the pulmonary and/or aortic vasculature, and/or between the parietal pleura and diaphragm.2 A pleural effusion—particularly on the patient’s left side—should raise concern for esophageal perforation.