16-year-old male presents with moderately severe acute wheezing

Both lungs are hyperaerated, consistent with acute asthma. Vertical air densities are seen in the upper mediastinum extending up into the soft tissues of the neck and there is evidence of air around the heart.

In a pneumomediastinum, the lateral view will often show air dissecting along the trachea or free air may be visible in the space anterior to the heart in the thymic region. In this case, free air in the thymic region is visible, but it may be difficult to see on your computer monitor. There are vertical oblique air densities in the thymic space anterior and superior to the heart on the lateral view. Darken the room and adjust the contrast and brightness on your monitor to see this best.

Both lungs are hyperaerated. There are vertical air densities seen in the upper mediastinum extending up into the soft tissues of the neck. There is evidence of air dissecting along the left border of the cardiac silhouette and outlining the thymus. There is no evidence of pneumothorax. Impression: Pneumomediastinum.

References:
Marx: Rosen's Emergency Medicine, 7th ed.: Mosby; 2009. CHAPTER 71 - Asthma
Marx: Rosen's Emergency Medicine, 7th ed.: Mosby; 2009. CHAPTER 43 - Abdominal Trauma