Small intrahepatic mass-forming cholangiocarcinoma: target sign on diffusion-weighted imaging for differentiation from hepatocellular carcinoma.

PURPOSE

To determine the differential MRI features of small mass-forming intrahepatic cholangiocarcinoma (ICC) from hepatocellular carcinoma (HCC).

METHODS

Sixty-four patients with pathologically proven small ICCs (n = 32) and HCCs (n = 32) (≤ 3.0 cm in diameter) who had undergone preoperative gadoxetic acid-enhanced MRI and DWI were enrolled in this study. Images were analyzed for the shape of the lesions, the presence of biliary dilatation, hyperenhancement (>50 % of the tumor volume) or rim enhancement on the arterial phase, capsular enhancement, and the presence of target appearance (a central enhancement with hypointense rim) on the hepatobiliary phase and on DWI (a central hypointense area with a peripheral hyperintense rim). Statistical significance of these findings was determined by the χ(2) or Fisher's exact test. Multivariate analysis was performed to identify independent imaging findings that allow differentiation of the two diseases.

RESULTS

Univariate analysis revealed that the following significant parameters favor ICC over HCC: lobulating shape, rim enhancement on arterial phase, target appearance on the hepatobiliary phase, and DWI (P < 0.05). Multivariate logistic regression analysis revealed that only target appearance on the DWI was a significant and independent variable predictive of ICC, as 24 ICCs (75.0 %) and one HCC (3.1 %) showed this feature (P = 0.0003).

CONCLUSION

A target appearance on the DWI was the most reliable imaging feature for distinguishing small mass-forming ICC from small HCC.