Pneumomediastinum

Refers to air in the mediastinal space. Can occur secondary to alveolar rupture in asthma, esophageal rupture (e.g., Boerhaave syndrome), or sometimes even bowel rupture when there is communication between the abdominal and thoracic cavities.

Case #1. Continuous diaphragm sign present (linear lucency below cardiac shadow). A pneumothorax is also present.