From the case:
Pneumopericardium
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Frontal

X-rays of the chest demonstrate the heart to be outlined by air, consistent with pneumopericardium.
Case Discussion
These images are from Dr. Paula Brill's excellent pediatric radiology collection.
Dr. Brill is a professor in the department of radiology (pediatric section) at Weill Cornell.
This case was donated to Radiopaedia.org by Radswiki.net.