Gadoxetic Acid-Enhanced Magnetic Resonance Imaging for Differentiating Small Hepatocellular Carcinomas (≤2 cm in Diameter) From Arterial Enhancing Pseudolesions Special Emphasis on Hepatobiliary Phase Imaging

Objectives: To determine the characteristic enhancing features of hepatocellular carcinoma (HCC) and arterial-enhancing pseudolesion (AEP) on gadoxietic acid (Primovist (R))-enhanced magnetic resonance imaging (MRI) and to assess its performance compared with that of multirow detector computed tomography (MDCT) for differentiating small HCC (<= 2 cm in diameter) from AEP in cirrhotic liver. Materials and Methods: A total of 69 patients with 97 small, arterial enhancing hepatic lesions (0.5-2 cm in diameter), ie, 44 HCCs and 53 AEPs, detected on gadoxetic acid-enhanced MRI, were included in this study. HCCs were diagnosed either through histopathology confirmation (n = 16) or by a combination of liver computed tomography (CT), angiographic findings, lipiodol CT, and AFP levels (n = 28). AEPs were diagnosed either through histopathology confirmation (n = 2) or were based on the angiographic findings, liver CT, and follow-up imaging (n = 5 1). Two radiologists jointly analyzed the morphologic features and the enhancement characteristics on the gadoxetic acid-enhanced MRI. Of the 69 study patients, 42 patients with 60 arterial enhancing lesions underwent quadruple-phase CT in addition to their MRI examination within 4 weeks before or after the MRI, and 2 other radiologists who were blinded to the final diagnosis independently reviewed the MRI and CT images in random order, at an interval of 2 weeks. Diagnostic performance was evaluated using receiver operating characteristics. The Kappa test was used to evaluate interobserver agreement. Results: Among 44 HCCs, 42 (95.4%) demonstrated low signal intensity (SI) and only 2 showed iso- or high SI on the hepatobiliary phase of gadoxetic acid-enhanced MRI. Alternatively, most AEPs showed iso SI on the hepatobiliary (n = 50, 94.3%) phase, and only 2 AEPs showed low SI. Compared with the diagnostic performance of the 2 imaging modalities, the mean areas under the receiver-operator characteristic curves on MR imaging were 0.975 for reviewer I and 0.966 for reviewer 2, whereas those of CT imaging were 0.892 for reviewer I and 0.888 for reviewer 2 (P = 0.069 and P = 0.106, respectively). The sensitivity for each reviewer with MR imaging (93.9% and 90.9%, respectively) was significantly higher than that with multiphasic CT (54.5%, in both) (P = 0.001 and 0.0018, respectively). Conclusion: HCCs and AEPs show different enhancing features on the delayed dynamic and hepatobiliary phases of gadoxetic acid-enhanced MRI. Gadoxetic acid-enhanced MRI may, therefore, help to differentiate between HCC and AEP.