Spontaneous Pneumomediastinum and Macklin Effect: Three Rare Case Reports with Computed Tomography Findings

Abstract

Spontaneous pneumomediastinum (SPM) is defined as free air or gas in the mediastinum that is not associated with an obvious cause  such as chest trauma. The SPM results from acutely elevated intra-alveolar pressure: The high-pressure gradient between the distal  alveoli and the pulmonary interstitium leads to alveolar rupture. This causes free gas to separate through the peribronchovascular fascial sheaths (interstitial emphysema) into the hilum and then into the mediastinum. Once the gas is in the mediastinum, it can travel up to  the cervical soft tissues (even the retroperitoneum) producing subcutaneous emphysema. The Macklin effect appears on thoracic  computed tomography (CT) as linear air collections adjacent to bronchovascular sheaths. This case report presents CT findings of SPM  due to the Macklin effect in three cases and a brief literature review on this subject.