Accessory lobe of the right liver mocking a pulmonary tumor in an adult woman

We report a rare case of an accessory lobe of the liver in the right thoracic cavity with the past history of breast cancer. A 66-year-old woman underwent thoracotomy owing to a slowly growing suspected lung tumor identified by computed tomography. The intraoperative findings revealed an accessory lobe of the liver. If this possibility had been considered, the correct diagnosis could have been achieved using computed tomography with multi-directional scanning, so that an unnecessary operation could have been avoided.