Small Intrahepatic Cholangiocarcinoma and Hepatocellular Carcinoma in Cirrhotic Livers May Share Similar Enhancement Patterns at Multiphase Dynamic MR Imaging.

Purpose: To assess the accuracy of magnetic resonance (MR) imaging-based differential diagnosis of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) in a cohort of patients with focal liver lesions and cirrhosis. Materials and Methods: This study was institutional review board approved, and the requirement for informed consent was waived. Between January 2009 and December 2014, a cohort of cirrhotic patients, including 71 with ICC and 612 with HCC, underwent unenhanced T1- and T2-weighted MR imaging, gadolinium-based contrast material-enhanced dynamic phase imaging, and partial hepatectomy. Results of patho-logic examinations were obtained for all patients. Clinical, radiologic, and pathologic results in these patients were analyzed and compared comprehensively. Differences in signal intensity on baseline and contrast material-enhanced images and dynamic enhancement patterns were evaluated and compared by using the chi(2) test or the Fisher exact test. Results: The preoperative diagnoses of 517 of 683 lesions were confirmed pathologically. Five ICCs and 481 HCCs displayed contrast material washout in delayed phases (P < .001). Thirty-six ICCs and 23 HCCs displayed a progressive enhancement pattern (P < .001). Twenty-six ICCs and 63 HCCs displayed a stable enhancement pattern (P < .001). ICCs displayed significantly different enhancement patterns according to size (P = .022). Conclusion: The accurate discrimination of small ICCs from HCCs in the setting of cirrhosis at MR imaging is difficult, as substantial proportions of ICCs and HCCs have similar enhancement patterns. Absence of contrast material washout at MR imaging is not a factor that prevents the misdiagnosis of HCC. (C) RSNA, 2016