MRI of Small Hepatocellular Carcinoma: Typical Features Are Less Frequent Below a Size Cutoff of 1.5 cm.

ABSTRACT

OBJECTIVE: The purposes of this study were to analyze MRI features of small hepatocellular carcinomas (HCCs) on the basis of size and to evaluate the difference in frequency of typical radiologic hallmarks of HCC (arterial enhancement and washout) according to the tumor size. MATERIALS AND METHODS: Enrolled were 86 patients with 110 HCCs 3 cm or smaller who underwent surgical resection or transplantation. Two radiologists reviewed gadoxetic acid-enhanced MRI features for signal intensity of T2-weighted and T1-weighted imaging, diffusion restriction, presence of arterial enhancement, washout on portal and transitional phases, and signal intensity on the hepatobiliary phase. ROC curve analysis was performed to determine the optimal HCC cutoff size for radiologic hallmarks of HCC. Tumors were divided into two groups by cutoff size, and the frequencies of MRI features were assessed. RESULTS: On ROC analysis, the optimal cutoff for radiologic hallmarks of HCC was 1.5 cm in independent and consensus reviews by two radiologists. HCCs smaller than 1.5 cm showed typical finding of HCC less frequently than HCCs 1.5 cm or larger in diameter. In subgroup analyses, HCCs with diameters between 1 and 1.5 cm showed similar MRI findings to HCCs with diameters 1 cm or less but significantly different findings compared with HCCs with diameters from 1.5 to 2 cm and 2-3 cm. CONCLUSION: HCCs smaller than 1.5 cm in size less frequently showed MRI findings seen typically in larger HCCs. Therefore, small HCCs are harder to detect with certainty not only because of small size but also because of the lower frequency of typical MRI findings.