The first sonographic evaluation of pneumomediastinum was first described as “air gap sign” . It was described as a broad band of echoes due to accumulation of air obscuring the anterior wall of the heart, with drop out echoes posteriorly. Pneumomediastinum appeared cyclically with the cardiac cycle . In 1994, Allgood et al.  described sonographic pneumopericardium findings as the inability to view the heart at the subxiphoid area. This was due to a potential space behind the pericardium that extended inferiorly to the posterior of the pericardium. However, in pneumomediastinum, the heart can be visualized at the subxiphoid area as it was well intact with the diaphragm without obstruction of the air. If there is air in the abdomen (pneumoperitoneum) or if the presence of large gastric bubble, this can obscure the subxiphoid view, thus differential of pneumopericardium and pneumomediastinum can be difficult. The difference in ultrasound findings between pneumopericardium and pneumomediastinum was recently described by Zachariah et al. . In pneumomediastinum, the subxiphoid window remained clear and anatomy is not obscured, suggesting that diaphragm, pericardium, and myocardium were still intact and not obstructed by air. In pneumopericardium, views for parasternal long, parasternal short apical four chambers, and subxiphoid view were poor quality with diffuse A-lines, suggesting air artifact.
Point-of-care ultrasound performed at bedside can lead to a diagnosis that clinical examination alone would not have revealed. Pneumopericardium is not an easy diagnosis to make either clinically or sonographically. Although there is the literature describing pneumopericardium findings, to the best of our knowledge, there is no previous report for trauma cases. FAST scan is a standard ultrasound protocol and is used as an adjunct in primary survey according to the ATLS guidelines. However, the purpose of FAST was to look for free fluid in pericardial and peritoneal regions and, of recent years, presence of haemo- and pneumothorax. With the advancement of knowledge in ultrasound, FAST protocol can be taken to another level. The placement of the probe at the same place as in FAST scan, other pathologies can also be identified, such as atelectasis and diaphragmatic hernia [6, 7]. In our case, partial visualization of the cardiac image with the presence of A-lines on subxiphoid view, coupled with A-lines on all other cardiac views, is highly suggestive of pneumopericardium.