Thoracic duct cyst presenting as an hour-glass shaped mass in the left supraclavicular area: case report. Thoracic duct cysts are a very rare entity in the head and neck pathology. We present a case of a 52 year-old man, who was referred to our service, complaining by a 30 days left cervical mass, with no other symptoms. A 6 cm cystic mass was revealed after ultrasonography and CT. Needle aspiration confirmed the presence of lymph in the cyst. The treatment was simple excision. Special care was taken to ligate the connected lymphatic vessels.