[A case of right atrial thrombus associated with idiopathic pericarditis].

A 73-year-old man suffering from exertional dyspnea was admitted to our hospital. Transthoracic echocardiography revealed pericardial effusion. This case was diagnosed as idiopathic pericarditis from laboratory data and pathological findings of the pericardial biopsy. A right atrial mass was detected by computed tomography, transesophageal echocardiography and MRI during conservative treatment. Because of the risk of pulmonary embolism due to the presence of the right atrial mass, removal of the mass was performed. The atrial mass was diagnosed as organized thrombus by pathological examination. It was suggested that the cause of right atrial thrombus was congestion and damage of the right atrial endocardium due to idiopathic pericarditis and atrial fibrillation. This case of a right atrial thrombus associated with idiopathic pericarditis is very rare, and MRI was proven to be very useful in the differentiation of a thrombus from cardiac tumor.