Morphology of intraductal papillary neoplasm of the bile ducts: radiologic–pathologic correlation

Purpose: Intraductal papillary neoplasm of the bile duct (IPN-B) is known as a premalignant lesion of invasive cholangiocarcinoma. The purpose of this study was for radiologic–pathologic correlation of morphologic features of IPN-B and to correlate the subclassifications with biological behavior in regard to the bile duct wall invasion. Materials and Methods: A pathologist classified gross morphology of 75 cases (44 men and 31 women, age range, 39–85) of histopathologically proven IPN-B into polypoid, cast-like, superficial-spreading, and cyst-forming type. Preoperative images were retrospectively reviewed by two observers independently and classified the gross appearance of intraductal tumors into the four types. Results: The pathologist classified macroscopic appearances of 75 cases of IPN-B into polypoid type in 26, cast-like intraductal growth in 17, superficial-spreading growth in 21, and cyst-forming type in 11. Two observers classified image findings in accordance with pathologist’s classification in 58 and 57 (77% and 76%) among the 75 cases of IPN-B, respectively; 18 and 19 of 26 cases of polypoid type, 14 and 14 of 17 cases of cast-like growth type, 16 and 19 of 21 cases of superficial-spreading type, 10 and 5 of 11 cases of cyst-forming type, respectively. Interobserver agreement for subclassification of tumor morphology was in the category of good agreement (k = 0.651). There was no correlation between morphological subclassification and tendency to invasive cholangiocarcinoma. Conclusion: IPN-Bs can be classified morphologically into polypoid, cast-like growth, superficial-spreading, and cystic type, but there is no correlation between the types and tendency to invasive cholangiocarcinoma.