Hemothorax with a High Carbohydrate Antigen 19-9 Level Caused by a Bronchogenic Cyst

A 58-year-old man presented with right-sided chest pain. Radiography and computed tomography showed a pleural effusion in the right chest and a mass in the right hilum. Thoracentesis showed a hemothorax. The carbohydrate antigen (CA) 19-9 level in the pleural effusion was very high, requiring differentiation from malignancy. Positron emission tomography showed no significant fluorodeoxy glucose (FDG) accumulation. Magnetic resonance imaging revealed a cystic lesion. The tumor was resected for both a diagnosis and treatment. A pathological examination demonstrated a bronchogenic cyst. An immunohistochemical study suggested that the cyst was the source of the hemothorax and the high CA19-9 level.