Unexpected case of pneumomediastinum and subcutaneous emphysema: primary or secondary aetiology?

A 77-year-old man was admitted with a relapse of antineutrophil cytoplasmic antibody-positive vasculitis with pulmonary involvement and acute kidney injury. There was a background of pulmonary fibrosis (non-specific interstitial pneumonia type pattern) and superadded pulmonary haemorrhage, acute pulmonary oedema and sepsis. The patient was intubated for 4 days and remained dependent on high flow oxygen and continuous positive airway pressure after extubation. A chest radiograph performed 2 weeks after extubation demonstrated unexpected, extensive pneumomediastinum and subcutaneous emphysema. This was confirmed on CT which raised the possibility of a tracheal defect at the level of the prior endotracheal tube cuff position. Tracheal injury was considered clinically unlikely due to the considerable interval since extubation and a short, uneventful intubation period. The cardiothoracic team recommended a diagnostic bronchoscopy but this was felt too high risk by the clinical team. The cause of pneumomediastinum and subcutaneous emphysema remained indeterminate.