[Mediastinal thoracic duct cyst--a case report].

The patient, a 55-year-old asymptomatic man, was referred to our hospital in October 1995 for further investigation of a chest ++roentogenographic abnormality found during a "physical check-up". His chest X-ray showed a round shadow over the hilus of the left lung. Computed tomography revealed a homogeneous, low density mass bordering the esophagus, vertebral column, left lower pulmonary vein and descending aorta. Roentogenography after swallowing barium sulfate showed that the esophagus was compressed and displaced to the right in the anterior direction. Endoscopic ultrasound scan demonstrated a cystic mass. The preoperative findings were suggestive of an esophageal cyst or a thoracic duct cyst. On December 12, 1995, the patient was operated on. The mass was 2 x 3 x 6 cm in size, and was easily separated from the left pulmonary vein, esophagus and vertebral column by blunt and sharp dissection, but it was strongly adhered to the aorta. The wall of the cyst was incised and a chylous fluid was found inside. The mass was diagnosed as a thoracic duct cyst and was removed after clipping and cutting the thoracic duct above and below the cyst. Histopathological features of the wall of the cyst was that the luminal surface was lined by a monolayer of flat endothelium and composed of loose fibrous tissue with scattered bundles of smooth muscle. It differed from that of veins. The postoperative course was uneventful and he was discharged on the 12th postoperative day. Mediastinal thoracic duct cysts are rare and only 25 operated cases have been reported in the literature. We review and discuss these cases.