Giant retrocardiac foregut duplication cyst presenting with left atrial compression and palpitations

A 35-year-old man presented with a 3-month history of palpitations and shortness of breath. An ECG showed premature atrial contractions and episodes of supraventricular tachycardia. A subsequent echocardiogram showed a retrocardiac cystic mass that was compressing the left atrium. A CT scan confirmed these findings by showing a large left-sided posterior mediastinal cyst compressing the left atrium and pulmonary veins. The cyst was successfully excised from the retrocardiac position via left thoracotomy after which there was complete resolution of the palpitations. Histopathology showed it to be a mediastinal cyst, most likely a foregut duplication of the enterogenic variant. This is an extremely unusual case of foregut duplication cyst presenting with compression of the left atrium and pulmonary veins leading to atrial arrhythmias.