Adenomyoma of common bile duct arising in a type I choledochal cyst

Adenomyoma can be misdiagnosed as an adenocarcinoma, leading to needless and extensive surgical resections. A 45-year-old woman presented with right hypochondrial pain. Magnetic resonance imaging showed a choledochal cyst. Excision of choledochal cyst with Roux-en-Y hepaticojejunostomy was performed. A segment of dilated common bile duct and an attached nodule was received. Sections from the choledochal cyst showed a cyst wall composed of dense fibrous tissue lined by partially ulcerated columnar epithelium. Sections from the nodule showed interlacing whorls of smooth muscle bundles with entrapped glands. The glands were lined by cuboidal to columnar cells without nuclear atypia. This was recognized as an adenomyoma. To the best of our knowledge, this is the first reported case in which an adenomyoma was found associated with a type 1 choledochal cyst. A review of the existing literature and discussion of theories of genesis and the diagnostic pitfalls are presented.