Differentiation Between Hepatocellular Carcinoma Showing Hyperintensity on the Hepatobiliary Phase of Gadoxetic Acid-Enhanced MRI and Focal Nodular Hyperplasia by CT and MRI

OBJECTIVE. The purpose of this study is to identify points useful in the imaging differentiation of hepatocellular carcinoma (HCC) showing hyperintensity on the hepatobiliary phase of gadoxetic acid-enhanced MRI and focal nodular hyperplasia (FNH) and FNH-like nodules. MATERIALS AND METHODS. We enrolled consecutive 51 pathologically diagnosed HCCs that were hyperintense on hepatobiliary phase imaging (47 patients, including 44 with cirrhosis) and 10 FNHs and eight FNH-like nodules (16 patients, including five with cirrhosis). Imaging findings of dynamic CT and gadoxetic acid-enhanced MRI were assessed by two radiologists and compared between HCC and FNH. RESULTS. The apparent diffusion coefficient (ADC) was lower in hyperintense HCC than in FNH (p = 0.004). The enhancement patterns of hyperintense HCC and FNH at dynamic CT were significantly different (p < 0.0001), with 95.9% of HCCs and 22.2% of FNHs showing arterial phase enhancement with a washout pattern, and 4.1% of HCCs and 77.8% of FNHs showing arterial phase enhancement without a washout pattern. The frequency of coronalike enhancement was 84.3% in hyperintense HCCs versus 11.1% in FNHs (p < 0.0001). The signal distribution on the hepatobiliary phase was significantly different between hyperintense HCCs and FNHs (p = 0.0002). The frequency of a capsulelike rim was 88.2% versus 22.2%, that of a mosaic appearance was 72.5% versus 11.1%, and that of a central scar was 0% versus 55.6% in hyperintense HCCs versus FNHs (all p < 0.0001). Multivariate logistic regression analysis showed that ADC ratio (p = 0.03; odds ratio, 0.12) and enhancement pattern at dynamic CT (p = 0.04; odds ratio, 16.21) were the independent factors for differentiation between hyperintense HCC and FNH. CONCLUSION. For the diagnosis of hyperintense HCC differentiated from FNH and FNH-like nodule, arterial phase enhancement and washout pattern at dynamic CT and decrease of ADC ratio would be important findings.