Left atrial compression by a mediastinal bronchogenic cyst presenting with paroxysmal atrial fibrillation.

Mediastinal bronchogenic cysts develop from abnormal budding of the primitive tracheobronchial tree. They are usually located in the mediastinum at the level of the tracheal bifurcation. In adults they are frequently asymptomatic and are discovered incidentally on the chest radiograph. As they enlarge they may cause symptoms referable to tracheal, bronchial, or oesophageal compression.' Extrinsic compression of the heart or great vessels appears to be a very rare occurrence.' 3