Acute pericardial diverticulum caused by pericarditis treated with drainage of pericardial effusion.

A 50-year-old woman was admitted with congestive heart failure due to cardiac tamponade, which was caused by acute pericarditis with pericardial effusion. Although images of contrast computed tomography (CT) obtained two weeks prior to admission had shown no abnormality, CT on admission showed a mediastinal tumor communicating with the pericardial cavity. It had rapidly appeared in a few weeks. We diagnosed it as acute pericardial diverticulum caused by acute pericarditis. They improved after treatment with antibiotic therapy and pericardial drainage. <Learning objective: This case suggests that acquired pericardial diverticulum could be caused by herniation due to increasing pressure of the pericardial cavity resulting from pericarditis.　The drainage of pericardial effusion decreased the pressure, so we could treat the acute phase of pericardial diverticulum.>.