CTICasesPneumomediastinum due to Macklin Phenomenon
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Imaging findings
A chest radiograph shows pneumomediastinum extending into the thoracic inlet and subcutaneous emphysema. Subtle signs include the 'double wall sign' (air outlining both the lumen and outer wall of the main bronchus) and a sharply defined cardiac margin due to air surrounding the heart's fat. On CT, 'lightning bolts' (black lines) of interstitial emphysema are visible within the alveolar septa, particularly in the middle lobe. Air is also seen tracking along the connective tissue sheath adjacent to the superior pulmonary vein, consistent with its dissection from alveolar rupture into the mediastinum.
Key takeaways
The Macklin phenomenon describes the mechanism of pneumomediastinum involving alveolar rupture, leading to air dissection into the peribronchovascular interstitium and subsequently into the mediastinum along vascular sheaths. Characteristic imaging signs include interstitial emphysema ('lightning bolts'), air tracking along pulmonary veins, the 'double wall sign' on radiographs, and clear outlining of mediastinal structures.
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