[Mediastinal esophago-bronchogenic cyst presenting as a single mass]

An abnormal shadow was found on a chest X-ray film of a 42-year-old man. The mass was 17 x 12 x 11 cm, smooth, round, homogeneous, and was seen in the left upper lung field. Chest computed tomography revealed a cystic mass in contact with the left lung, the chest wall, the esophagus, and the aorta. Magnetic resonance imaging showed a wall that divided the mass into two compartments. The cystic lesion was removed and was found to contain a yellow liquid. The larger part of the mass was histologically similar to esophageal wall and the smaller part was bronchogenic. The final diagnosis was mediastinal esophago-bronchogenic cyst. In previously reported cases, two cystic masses were connected by a canal. The findings in this case support the theory by Yoshii that this type of cyst originates from the diverticulum of the foregut near the lung bud.