[Incidentally Detected Right Atrial Blood Cyst]

A 48-year-old man underwent computed tomography for the examination of lower back pain, which incidentally detected a cardiac tumor in the right atrium. On echocardiography, the tumor was identified as a 30 mm round mass with a thin wall and iso- and hyper-echogenic contents that originated from the atrial septum. The tumor was successfully removed under cardiopulmonary bypass, and the patient was discharged in good health. The cyst was filled with old blood, and focal calcification was observed. Pathological examination revealed that the cystic wall was composed of thin-layered fibrous tissue lined with endothelial cells. Regarding a treatment, it is reported that early surgical removal is preferable to avoid embolic complications, however it is controversial. Furthermore, it needs to discuss about the difference between fetal/neonatal and adult cases.