What causes the ring-around-the-artery sign on chest radiographs?
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Mediastinal air tracking around the extrapericardial segment of the right or left pulmonary artery, seen in pneumomediastinum.
This finding is known as the ring-around-the-artery sign on lateral chest radiographs and chest CTs.
Why is it called so?
The name describes the distinct (semi-) circular radiolucent halo of air that outlines and surrounds the dense central pulmonary artery, appearing as a dark “ring” on imaging.
Pathophysiology:
In pneumomediastinum, free air from alveolar rupture (often due to asthma, barotrauma, or severe coughing) tracks proximally along the bronchovascular sheaths toward the pulmonary hilum—a process known as the Macklin effect. When this air reaches the mediastinum, it can collect around the mediastinal (extrapericardial) portion of the right pulmonary artery, rendering its outer wall visible against the surrounding gas and creating the classic ring-like lucency.
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