Pneumomediastinum

The presence of free air or gas within the mediastinum, usually due to alveolar, tracheobronchial, or esophageal disruption, and may be spontaneous, traumatic, or iatrogenic, sometimes progressing to tension pneumomediastinum or associated pneumothorax. Possible causes are increased airway pressure (airway blockage, asthma, COPD, coughing, sneezing, vomiting, weightlifting, the Valsalva maneuver, childbirth), trauma, iatrogenic (mechanical ventilator, bronchoscopy, endoscopy, chest/abdominal surgery), scuba diving, high-altitude flying, inhalation drugs (marijuana, crack cocaine).