Pneumomediastinum: NEET PG Essentials
1. Hallmark Radiographic Signs
- Continuous Diaphragm Sign: A crucial high-yield sign. Air beneath the heart allows the diaphragm to be seen as a continuous structure across the midline (usually, the heart silhouette obscures the middle part).
- Ring Around the Artery Sign: Air outlines the pulmonary artery or the aorta, making them appear as a distinct ring.
- Thymic Wing Sign: Seen in children; the thymus is lifted by air, making it look like the wings of a butterfly or angel.
- Double Bronchial Wall Sign: Air outlining both the inner and outer walls of the bronchi.
2. Clinical Context: The Macklin Effect
The Macklin Effect describes the pathophysiology: alveolar rupture → air tracking along bronchovascular sheaths → accumulation in the mediastinum.
| Etiology | High-Yield Clinical Note |
|---|---|
| Boerhaave Syndrome | Spontaneous esophageal rupture. Suspect if persistent vomiting followed by chest pain (Mackler triad: vomiting, chest pain, subcutaneous emphysema). |
| Asthma/Valsalva | Common trigger in younger patients: forceful coughing or breath-holding. |
3. Examination Pearls
- Hamman’s Sign: A crunching, rasping sound heard on cardiac auscultation that is synchronous with the heartbeat. Highly specific for pneumomediastinum.
- Subcutaneous Emphysema: Often accompanies pneumomediastinum; crepitus is felt on palpation of the neck or chest wall.
- Management: Generally conservative (oxygen therapy promotes nitrogen washout). However, if secondary to Boerhaave’s, it is a surgical emergency requiring immediate contrast studies (esophagram).