Stab wounds of the heart: two new signs of pneumopericardium.

The diagnosis of a small traumatic pneumopericardium may be difficult and differentiation from a left medial pneumothorax or pneumomediastinum is important. Two new signs which only occur in pneumopericardium are described: the "transverse band of air" sign on the frontal radiograph representing air in the transverse sinus of the pericardium, and the "triangle of air" sign as noted on the lateral radiograph. If there is still doubt, a left-side-down decubitus radiograph will establish the diagnosis.