A 14-year-old girl, with a previous history of controlled asthma without any chronic medication, was admitted to the emergency department with dyspnea, neck and chest pain. Without history of trauma, she only mentioned that a friend jumped on her back a few hours earlier. The primary examination revealed a blood pressure of 109/68 mmHg (50th percentile), heart rate of 89 beats/min and oxygen saturation of 97%, with palpable crepitus in the anterior chest wall and neck and diminished breath sounds in pulmonary auscultation. The rest of the physical examination was unremarkable. Electrocardiography shown normal sinus rhythm without QTc prolongation or axis deviation. Chest X-ray is shown on Figure 1.
Figure 1. Chest X-ray revealing pneumomediastinum and bilateral subcutaneous emphysema, over the neck and left side of chest wall (red arrows).
What is the diagnosis?