Mediastinal Extralobar Pulmonary Sequestration Concurrent With Spontaneous Pneumothorax: A Case Report of Difficult Preoperative Diagnosis.

Extralobar pulmonary sequestration (EPS) in the mediastinum is rare, and preoperative diagnosis can be challenging. We report a case of EPS in the middle mediastinum, where a congenital pericardial defect became apparent on computed tomography (CT) imaging as pneumopericardium concurrent with spontaneous pneumothorax. The patient presented with a left spontaneous pneumothorax. A chest plain CT revealed bullae in the apical segment of the left upper lobe and the S6 segment of the lower lobe, a 3.2 cm solid mass in the left middle mediastinum, and a pericardial defect with pneumopericardium beside the main left pulmonary artery. We initially considered the mediastinal mass to be a hematoma resulting from the rupture of adhesions between the lung and mediastinum due to the onset of spontaneous pneumothorax. We performed a bullectomy using video-assisted thoracoscopic surgery. Intraoperative findings revealed that the mediastinal mass was not a hematoma but solid tissue, raising suspicion of a mediastinal tumor. We transected the feeding artery and drainage vein using a vessel sealing system and resected the mediastinal mass. Histopathological examination revealed bronchial structures and lung parenchyma, confirming a diagnosis of EPS. The pericardial defect manifesting as pneumopericardium due to concomitant pneumothorax could have provided clues to an accurate preoperative diagnosis of EPS.