[Adult endocardial blood cyst; report of a case].

We report herein a rare case of endocardial blood cyst (EBC) in an adult patient. A 63-year-old asymptomatic woman underwent echocardiography, which incidentally detected a cardiac tumor in the right atrium. On echocardiography, the tumor was revealed to be a 30-mm round mass with thin, hyperechogenic walls and heterogeneously hypoechogenic contents. The lesion was attached to the septum. On computed tomography, the tumor appeared partly calcified and showed poor contrast-enhancement. On magnetic resonance imaging, the lesion appeared isointense or slightly hyperintense in T1 and T2-weighted sequences. Myxoma was strongly suspected based on these preoperative imaging findings. The tumor was successfully excised under cardiopulmonary bypass. Gross examination confirmed that the cyst was filled with blood. The cystic walls comprised thin-layered fibrous tissue lined with endocardial cells. No tumor cells were found. The diagnosis of EBC was confirmed based on histopathological examination, and the postoperative course was uneventful.