<b><i>Background:</i></b> To date, there are inconsistent data about relationships between diffusion-weighted imaging (DWI) and tumor grading/microvascular invasion (MVI) in hepatocellular carcinoma (HCC). Our purpose was to systematize the reported results regarding the role of DWI in prediction of tumor grading/MVI in HCC. <b><i>Method:</i></b> MEDLINE library, Scopus, and Embase data bases were screened up to December 2019. Overall, 29 studies with 2,715 tumors were included into the analysis. There were 20 studies regarding DWI and tumor grading, 8 studies about DWI and MVI, and 1 study investigated DWI, tumor grading, and MVI in HCC. <b><i>Results:</i></b> In 21 studies (1,799 tumors), mean apparent diffusion coefficient (ADC) values (ADC<sub>mean</sub>) were used for distinguishing HCCs. ADC<sub>mean</sub> of G1–3 lesions overlapped significantly. In 4 studies (461 lesions), minimum ADC (ADC<sub>min</sub>) was used. ADC<sub>min</sub> values in G1/2 lesions were over 0.80 × 10<sup>−3</sup> mm<sup>2</sup>/s and in G3 tumors below 0.80 × 10<sup>−3</sup> mm<sup>2</sup>/s. In 4 studies (241 tumors), true diffusion (<i>D</i>) was reported. A significant overlapping of <i>D</i> values between G1, G2, and G3 groups was found. ADC<sub>mean</sub> and MVI were analyzed in 9 studies (1,059 HCCs). ADC<sub>mean</sub> values of MIV+/MVI− lesions overlapped significantly. ADC<sub>min</sub> was used in 4 studies (672 lesions). ADC<sub>min</sub> values of MVI+ tumors were in the area under 1.00 × 10<sup>−3</sup> mm<sup>2</sup>/s. In 3 studies (227 tumors), <i>D</i> was used. Also, <i>D</i> values of MVI+ lesions were predominantly in the area under 1.00 × 10<sup>−3</sup> mm<sup>2</sup>/s. <b><i>Conclusion:</i></b> ADC<sub>min</sub> reflects tumor grading, and ADC<sub>min</sub> and <i>D</i> predict MVI in HCC. Therefore, these DWI parameters should be estimated for every HCC lesion for pretreatment tumor stratification. ADC<sub>mean</sub> cannot predict tumor grading/MVI in HCC.
Prediction of microvascular invasion of hepatocellular carcinoma with preoperative diffusion-weighted imaging
