Role of MRI with hepatospecific contrast agent in the identification and characterization of focal liver lesions: pathological correlation in explanted livers.

Aim: To assess the diagnostic performance of magnetic resonance imaging (MRI) with gadoxetic acid in the identification of hepatocellular carcinoma (HCC) nodules by comparison with histological findings.
Methods: In a cohort of patients suffering from cirrhosis of various etiologies (chronic hepatitis C virus (HCV) or hepatitis B virus (HBV), alcohol abuse, cryptogenic forms), we selected 17 patients affected by HCC who were eligible for liver transplantation on the basis of a computed-tomography (CT) total-body examination. Such patients also underwent an MRI examination under basal conditions, and with four dynamic phases, as well as a hepatobiliary phase acquired after at least 20 min and recognized by the excretion of contrast agent into the bile duct, following intravenous administration of 0.05 mol/kg of gadoxetic acid (gadoxetate disodium, Primovist(®); Bayer, Osaka, Japan). The MRI images were then evaluated in a double-blinded experimental setup by two radiologists experienced in imaging of the liver. The diagnosis of HCC was made in the presence of nodular lesions that showed typical or atypical enhancement patterns. The liver was subsequently explanted (on average 47.4 days after MRI evaluation), dissected into 1-cm samples, and histologically evaluated according to the classification of Edmondson-Steiner.
Results: At the histopathological examination, 46 nodules were identified, on average 2.7 nodules for each patient. Of these, 37 were hepatocellular carcinomas, 3 were characterized by histologically unrecognizable complete necrosis, and 6 showed high-grade dysplasia. MRI with hepatospecific contrast medium showed inter-observer average values of sensitivity, specificity, and diagnostic accuracy of 94.6, 90, and 93.6 %, respectively. In one case, a nodule was not identified by MRI with gadoxetic acid, even in the hepatospecific phase (false negative (FN)). This result could be implicated to the long time interval between the analysis and the explant (88 days). In another case, there was an overdiagnosis of a HCC with a typical nodular pattern (false positive (FP)), but which most likely should have been attributed to a previous echinococcus cyst. MRI analysis, in combination with the study of the hepatobiliary phase, also showed a greater sensitivity, the same specificity, and a greater diagnostic accuracy compared to MRI evaluated only in the dynamic phases (with an average percentage between the two operators, respectively, of 75.7, 90, and 78 %).
Conclusions: MRI with gadoxetic acid shows a diagnostic accuracy superior to contrast-enhanced MRI, allowing for the diagnosis of additional lesions, and it could be considered as an imaging method to carry out a more appropriate management of waiting lists for liver transplants.