[A case of pericardial cyst associated with atrial septal defect]

A 51-year-old woman with an abnormal shadow in the right upper mediastinum and systolic heart murmur was diagnosed as mediastinal cyst and atrial septal defect (ASD). Before the operation, the cyst was suspected as bronchogenic cyst or cystic thymoma based on the findings by CT and NMR. Both cystectomy and closure of ASD was successfully performed and the cyst was diagnosed as pericardial cyst by pathological examination. A brief of literature on the pericardial cyst is given.