A 71-year-old man presented to our hospital for dyspnea lasting for the past 3 days. Chest X-ray and computed tomography demonstrated right tension pneumothorax, and an electrocardiogram suggested acute inferior myocardial infarction. Despite the relief of tension pneumothorax, the electrocardiographic findings were not completely resolved. Emergency coronary angiography demonstrated an occlusive lesion in the right coronary artery, and percutaneous coronary intervention was performed successfully. Thereafter, the chest tube was removed, and he was discharged. While rare, multiple life-threatening diseases that present with similar symptoms can coexist, so a re-evaluation after performing the initial treatment for one of these diseases is crucial.

We report here a case of a patient who underwent surgical resection of a giant pericardial cyst that was growing rapidly, causing anterior chest pain. An asymptomatic 56-year-old woman underwent a complete medical checkup in a health-care center. Her chest X-ray showed an unusually large bulge on the left cardiac border, and she was referred to our hospital. The chest X-ray taken 2 years ago in another hospital showed similar bulge on the same left cardiac border, but it was noticeably smaller. Chest CT revealed a 9.5 × 4.5 cm pericardial cyst within the anterolateral aspect of the left cardiac border. The CT number of the mass was approximately 15 - 20 HU. The mass also showed slight hyperintensity on T1-weighted MR images and hyperintensity on T2-weighted MR images. Four weeks later, she experienced anterior chest pain for the first time, and the chest X-ray and CT showed an increase in the size of the pericardial cyst. The CT number of the mass increased to approximately 30 - 40 HU. The cyst was successfully removed by video-assisted thoracic surgery. The pericardial cyst was diagnosed as benign according to the results of histopathology. We conclude that the rapid growth of the pericardial cyst was caused by intracystic hemorrhage that originated from vascularized connective tissue in the cyst wall