Small intrahepatic peripheral cholangiocarcinomas as mimics of hepatocellular carcinoma in multiphasic CT.

PURPOSE: Liver transplant guidelines for diagnosing hepatocellular carcinoma (HCC) do not mandate pathologic confirmation; instead, 'classic' imaging features alone are deemed satisfactory. Intrahepatic peripheral mass forming cholangiocarcinoma (IHPMCC) is a relative contraindication for transplantation due to high rate of recurrence and poor prognosis. This study examines the imaging findings of IHPMCC, to aid in the identification and differentiation from potentially confounding cases of HCC.

METHODS: After IRB approval, 43 tissue-proven cases of IHPMCC on multiphase CT were retrospectively reviewed by 2 fellowship-trained radiologists. Tumor size, presence of cirrhosis, tumor capsule, vascular invasion, tumor markers, and enhancement pattern were assessed. A grading system was assigned as determined by enhancement pattern to background liver on arterial, portal venous, and equilibrium phases, ranging from typical HCC to typical IHPMCC enhancement pattern.

RESULTS: Analysis based on our grading system shows 5 (11.6%) tumors demonstrating grade 1-2 enhancement, 9 (21%) grade 3-4 enhancement, and 29 (67.4%) grade 5 enhancement. Kruskal-Wallis test comparing CA19-9 between the five groups, Wilcoxin rank-sum test comparing tumor markers with presence or absence of tumor capsule, vascular invasion and cirrhosis, and nonparametric Pearson's correlation coefficient comparing tumor markers to tumor size were not statistically significant (p > 0.05).

CONCLUSION: Typical enhancement pattern of IHPMCC consisting of arterial phase hypoenhancement with progressive, centripetal-delayed enhancement is present in the majority of cases (68%). Five cases (11.7%) showed enhancement features potentially mimicking HCC, all of which are under 3.5 cm in size. Thus, small hyperenhancing lesions in a cirrhotic liver should be carefully scrutinized in light of differing therapy options from HCC, particularly in transplant situations.