Background: The presence of a mediastinal mass or a malignant tumor is the most common reason for thoracotomy and resection.Case Report: The authors have described a 71-year-old male patient who was admitted to hospital for abnormal mediastinal shadow. CT and plain X-ray did not reveal the existence of an aortic arch aneurysm. The patient was operated on via left thoracotomy and the diagnosis was made.Conclusions: The explorative thoracotomy should be carried out in the cases of mediastinal localisation of the tumor. The presented case is an example of intraoperative diagnosis due to localisation of the mediastinal mass in CT, not readily accessible for clinical or accessory investigation.

Keywords: aortic arch aneurysm, chest radiograph, mediastinal-neoplasms-diagnosis