Posttraumatic tension pneumopericardium: the "small heart" sign.

Radiographic measurements of the cardiothoracic ratio in four adult victims of blunt thoracic trauma with pneumopericardium demonstrated a sudden, substantial decrease in the size of the cardiac silhouette, which was accompanied by pathophysiologic effects of cardiac tamponade. The sudden decrease in cardiac size could not be attributed to a decrease in intravascular volume or to changes in positive airway pressure. Following surgical relief of tension pneumopericardium, the cardiac size was restored to baseline dimensions and the hemodynamic effects of tamponade resolved. In the presence of pneumopericardium, the "small heart" sign may alert one to the presence of tension pneumopericardium and impending cardiac tamponade.