Thoracoscopic resection of a thoracic duct cyst that developed during follow-up for a thymic cyst

A 29-year-old man had been diagnosed with an anterior mediastinal cyst 6 years earlier and was undergoing follow-up. At a follow-up visit, a newly developed cystic lesion was found in the middle mediastinum; therefore, the anterior mediastinal cyst and the middle mediastinal cyst were resected by thoracoscopic surgery. It was observed that the middle mediastinal cyst originated from the thoracic duct, and the thoracic duct was clipped. Pathologically, the diagnosis was a thymic cyst of the anterior mediastinum and a thoracic duct cyst of the middle mediastinum. The patient developed chylothorax after surgery, and a second thoracoscopic operation was performed. It revealed that part of the clipping of the caudal thoracic duct was incomplete, and leakage of chyle was observed. Hence, the clipping was performed again. The course after the second surgery was good. Thoracic duct cysts are rare even among mediastinal cysts and thus require caution due to their tendency to expand.