A 28-year-old female attended an outpatient clinic in October, 1989, b
ecause of a tumor in the left supraclavicular fossa, detected in a hea
lth examination, Following exploratory puncture of the tumor which yie
lded milky-white fluid, suggesting a cyst in the thoracic duct, she wa
s admitted to our department. The cyst was unilocular measuring about
6 cm in diameter, and the fluid content was chyle-rich in lipids, Lymp
hography demonstrated a lymphatic structure adjacent to the lesion and
scattered lymph vessels on the cyst surface, On November 16 the cyst
was resected. A restiform structure was observed between the cyst and
the thoracic duct, but the presence or absence of communication was un
clear. The histological diagnosis was thoracic duct cyst, Thoracic duc
t cyst occurring in the cervical region is very rare, Our case may pro
vide useful information as to its pathogenesis and the mode of retenti
on of cyst fluid.