Pneumomediastinum 2017-04-23T12:21:33Z Spontaneous pneumomediastinum (SPM) is defined as the non-traumatic presence of free air in the mediastinum in a patient with no known underlying disease. The most common etiology for SPM is alveolar rupture, most commonly due to an asthma exacerbation, but also seen with barotrauma, intrathoracic pressure increase, the valsalva maneuver, and withdrawal symptoms of illicit drugs. Other causes of pneumomediastinum include coughing, mechanical ventilation, pneumonitis, emphysema, lung fibrosis, acute respiratory distress syndrome, heroin, marijuana, cocaine use, gas producing infections in the head and neck, tracheobronchial or esophageal rupture and facial fractures that lead to disruption of maxillary sinus walls. The presence of free air in the mediastinum. Abnormal mediastinum morphology