2013 67 4 239 244 The Diagnosis of Hypovascular Hepatic Lesions Showing Hypo-intensity in the Hepatobiliary Phase of Gd-EOB- DTPA-enhanced MR Imaging in High-risk Patients for Hepatocellular Carcinoma a* a,b a,c a a a a a a a a b c
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August 2013 Diagnosis of Hypovascular HCC with EOB 243 Fig. 1 Typical findings of hypovascular hepatocellular carcinoma (HCC). A, T1-weighted enhanced MRI (arterial phase); B, Abdominal MRI (diffusion weighted image, b 1,000); C, Gd-EOB-DTPA-enhanced MRI (hepatobiliary phase); D, Abdominal ultrasonography; E, Histological finding of biopsied specimen (well-differetinated HCC). is inhibited in malignant liver lesions, such that they appear hypointense at the hepatobiliary phase [9]. Because so-called early HCCs do not show a classical HCC pattern, which is enhancement at an early arterial phase and washout at a portal venous phase, it is very difficult to distinguish them from other nonmalignant liver nodules by traditional imaging modalities. In the present study, we found that 74.3ｵ of hypovascular nodules that showed hypointensity at the hepatobiliary phase of EOB-MRI were HCCs. This PPV for the diagnosis of small hypovascular HCC is relatively high compared with other imaging modalities. Tajima. reported that only 9 of 19 (47ｵ) liver nodules showing hypoattenuation on CTHA were diagnosed as well-differentiated HCC [18]. Also, Hayashi. reported that 1 of 9 (11ｵ) liver nodules showing isoattenuation or hypoattenuation on CTHA and hypoattenuation on CTAP were diagnosed as well differentiated HCC [5]. Recently, other liver-specific contrast agents have been used, and those agents can also reveal hypovascular HCCs in some cases. Superparamagnetic iron oxide (SPIO) is a tissue-specific MR imaging contrast that is taken up by Kupffer cells in the liver; however, most of the well-differentiated HCCs had a similar number of Kupffer cells in the tumorous and nontumorous tissues. Therefore, it is difficult to distinguish dysplastic nodules from well-differentiated HCCs by SPIO-enhanced MR imaging alone [19]. Sonazoid is a lipid-stabilized suspension of perfluorobutane and is also taken up by the Kupffer cells. According to a recent report, only 3 of 13 (23.1ｵ) well-differentiated HCCs showed a perfusion defect in the Kupffer phase so that the diagnosis of hypovascular HCC by this method is also limited [20]. In our study, PPV of EOB-MRI at the hepatobiliary phase was high (74.3ｵ); however, the result is somewhat unsatisfactory because the false positive rate was 26ｵ. To achieve a higher PPV, we combined it with 3 independent factors: washout appearance at the delayed phase on triple-phase CT, the existence of a hypoechoic region in conventional US B-mode, and hyperintensity in DWI. As shown in Table 3, the PPV was raised to about 80ｵ when combined with one factor, and increased to almost 90ｵ when combined with 2 factors. When all 3 factors were positive, PPV reached 100ｵ. Liver biopsy for the diagnosis of HCC has several potential risks, such as intra-abdominal bleeding and the dissemination of tumor cells. The combination of examinations that we
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