A 45-year-old woman was admitted with chest pain and abnormal chest X-ray photograph findings which revealed a 6×5cm homogenous shadow in the left hilar region. Mediastinal tumor was suspected. After left thoracotomy, a cystic tumor measuring 6×5×5cm was removed. The tumor was diagnosed histopathologically as a blood cyst formed by rupture of preexisting abnormal venous vessels.
