Extralobar sequestrations constitute a rare form of congenital pulmonary airway malformations that are difficult to diagnose. Here, we report a rare case of a localized extralobar sequestration in the right superior portion of the mediastinum accompanied by congenital cystic adenomatoid malformation. A 19-year-old man presented with a right upper mediastinal mass that was detected using chest radiography, had a history of left spontaneous pneumothorax, and had undergone a bullectomy 4 years previously. The initial diagnosis included a mature teratoma and a bronchogenic cyst in the mediastinum; however, the presence of a cystic mass in the right upper lobe of the lung prompted further examination. A preoperative diagnosis of extralobular sequestration was finally determined using contrast-enhanced computed tomography. The aberrant artery was connected to the brachiocephalic artery, and its drainage vein was connected to the right pulmonary artery, uniquely behind the pericardium. Despite the unique location, right mediastinal extralobular sequestration with a congenital cystic adenomatoid malformation in the right upper lobe was confirmed pathologically. Examination of contrast-enhanced chest computed tomography (CT) and three-dimensional computed tomography images enabled a correct diagnosis. It is very important for surgeons to correctly diagnose and identify an aberrant artery and drainage vein to prevent uncontrolled hemorrhage.
