Slide 1: Where is the abnormal air located?
Slide 2: Air is located in subcutaneous tissues and the mediastinum. Mediastinal air is called pneumomediastinum. X-ray showing air in the mediastinum, displacing the pleura laterally. X-ray also showing subcutaneous air at neck and subcutaneous air at chest wall.
Slide 3: How could air have gotten into the mediastinum? CT confirms subcutaneous and mediastinal air.
Slide 4: The air could have gotten there after esophageal or tracheobronchial rupture. Esophageal rupture may occur after vomiting, or these structures may be torn following blunt or penetrating trauma. CT showing retained esophageal chicken bone with esophageal rupture and pneumomediastinum.
Slide 5: In non-penetrating injuries (blunt trauma, positive pressure ventilation, valsalva maneuvers), over distention of alveolus and subsequent rupture can result in pneumothorax and/or pneumomediastinum. If rupture communicate with pleural, this leads to pneumothorax. If rupture is in lung parenchyma, the gas dissects along bronchovascular bundles to the mediastinum leading to pneumomediastinum. This phenomenon is known as the Macklin effect. Shown in yellow arrows. The shared mechanism explains why pneumothorax and pneumomediastinum are so often seen together. Graphic of lung showing pneumothorax after alveolar rupture into pleural space and air dissecting back to the mediastinum.
Slide 6: An example of a patient with a pneumothorax and a pneumomediastinum. CT scan showing pneumothorax, pneumomediastinum, and air dissecting back along bronchovascular bundles to the mediastinum. Unfortunately, the clinical picture is sometimes confusing. For example, if a patient presents with pneumomediastinum after vomiting, is it due to esophageal rupture or the Macklin Effect? A lot of those patients end up with a chest CT or a contrast swallow ordered by some poor PGY 20 T-surg fellow.
- Knipe H. Pneumomediastinum. Radiopedia. Published 2017 Jun 16. rID 53639.
Tags: chest radiology, ct, lung, macklin effect, Mediastinum, pneumomediastinum, radiologist, radiology, xray