Carcinoid tumor arising in the wall of a congenital bile duct cyst.

We report an extremely rare case of carcinoid tumor arising in a congenital choledochal cyst. The dilated choledochal cyst in a 66-year-old Japanese woman was surgically resected, after which the ovoid elevated tumor, measuring 1.5 x 1.5 cm, was detected in the proximal portion of the cyst. A carcinoid tumor was histologically confirmed. To the best of our knowledge, this is the first published case of carcinoid tumor in a choledochal cyst.