Cholangiocarcinoma developing after simple excision of a type II choledochal cyst.

We have reported the fourth case of cholangiocarcinoma associated with a resected diverticulum of the common bile duct (type II choledochal cyst). The malignancy developed 2 years after adenomatous hyperplasia was demonstrated by simple excision of the cyst. We hypothesize that adenomatous hyperplasia is an early phase of malignant transformation in such patients. We believe the finding of adenomatous hyperplasia is of considerable importance in determining the extent of surgical resection.