Grading of small hepatocellular carcinomas (≤2 cm): correlation between histology, T2 and diffusion-weighted imaging

Objective: To evaluate the capacity of diffusion-weighted imaging (DWI) to determine the histological grade of small-sized hepatocellular carcinomas (HCCs) in liver cirrhosis in comparison with T-2 weighted imaging. Methods: 51 cirrhotic patients with 63 histologically proven HCCs <= 2 cm underwent abdominal MRI, including DWI (b-values 50, 400 and 800smm(-2)) and T-2 weighted sequences. HCCs were classified into well-differentiated HCCs (n=37) and moderately differentiated HCCs (n=26). Relative contrast ratios (RCRs) between the lesions and the surrounding liver were performed and compared between the two groups for T-2 weighted images, each b-value and apparent diffusion coefficients (ADCs). A receiver operating characteristic (ROC) analysis was performed to compare RCRs in T-2 and diffusion-weighted images. Results: We found significant differences in RCRs between well-differentiated vs moderately differentiated HCCs for b=50, 400 and 800smm(-2) and T-2 weighted images (1.35 +/- 0.36 vs 1.86 +/- 0.62; 1.35 +/- 0.38 vs 1.82 +/- 0.60; 1.27 +/- 0.30 vs 1.74 +/- 0.53; 1.14 +/- 0.18 vs 1.43 +/- 0.28, respectively; p<0.001), whereas no significant differences were observed in ADC and ADC RCR (1.05 +/- 0.19 vs 0.99 +/- 0.15 and 1.1 +/- 0.22 vs 1.09 +/- 0.23; p=0.16 and p=0.82, respectively). No significant difference was found in the areas under the ROC curve for RCRs of T-2 weighted images and every DWI b-value (p=0.18). Conclusion: The RCR measurement performed in DWI 50, 400 and 800 b-values and T-2 demonstrated a significant difference between well-differentiated and moderately differentiated small-sized HCCs. Furthermore, no difference was shown by using either ADC or ADC RCR. Advances in knowledge: DWI with RCR measurement may be a valuable tool for non-invasively predicting the histological grade of small HCCs.