Impending cardiac herniation: the snow cone sign.

Two cases of cardiac herniation and volvulus that occurred after right pneumonectomy are presented. Both asymptomatic patients demonstrated an unusual bulging contour to the right side of the heart on radiographs obtained in the recovery room, before complete herniation and volvulus occurred. In an autopsy preparation, a similar right contour was produced after partial cardiac herniation through a pericardial defect. The hemispheric contour from partial cardiac herniation resembles the shape of a snow cone. Clinical awareness of this sign of impending herniation is important, so risk factors known to produce herniation may be modified.