CTICasesMacklin Phenomenon (Pneumomediastinum)
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Imaging findings
Subtle radiographic findings include small slips of air traversing the thoracic inlet and outlining a mediastinal structure (a vessel in the superior mediastinum), with a subtle double wall sign along the superior wall of the left mainstem bronchus. CT confirms pneumomediastinum, with air dissecting into the mediastinum in relation to bronchovascular bundles and connective tissue sheets of pulmonary vein branches. There is also subpleural interstitial emphysema related to portions of the interlobar fissures, and septal emphysema with 'black lightning bolts' in the right middle lobe. No pneumomediastinum around the esophagus was observed.
Key takeaways
The Macklin phenomenon describes pneumomediastinum resulting from increased alveolar pressure (e.g., violent retching). This leads to alveolar rupture, interstitial emphysema, and dissection of air into the mediastinum. Subtle radiographic signs, such as mediastinal air outlining vascular structures or the 'double wall sign' of a bronchus, can indicate its presence. CT clearly demonstrates the extent of air dissection and associated interstitial emphysema.
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