Signal intensity of small hepatocellular carcinoma on apparent diffusion coefficient mapping and outcome after radiofrequency ablation

It has been reported that the apparent diffusion coefficient (ADC) value of hepatocellular carcinomas (HCC) on diffusion-weighted magnetic resonance imaging (MRI) is associated with their histological grade. The present study aimed to evaluate whether the signal intensity of small hypervascular HCC on the ADC map is related to the treatment outcome of radiofrequency ablation (RFA).Between February 2008 and August 2012, 136 consecutive patients with initial small hypervascular HCC (≤3 tumors and ≤3 cm in diameter) were examined by diffusion-weighted MRI before RFA. The signal intensities of HCC on the ADC map were visually compared with the surrounding liver and categorized as hypointense and non-hypointense. Critical recurrence was defined as more than three intrahepatic recurrences, recurrence with vascular invasion, seeding, dissemination and/or extrahepatic metastasis.The median follow up was 619 days. The cumulative 2-year recurrence rates of the hypointense and non-hypointense on the ADC map groups were 79% and 50% (P < 0.001), respectively, with cumulative 2-year local recurrence rates of 18% and 7% (P = 0.014) and cumulative 2-year critical recurrence rates of 38% and 13% (P = 0.005), respectively. The cumulative 3-year survival rates were 60% and 82% (P = 0.007), respectively. On multivariate analysis, hypointensity on the ADC map was the strongest independent factor related to recurrence and survival after RFA.The signal intensity of HCC on the ADC map was strongly associated with outcome after RFA. These results suggest that treatment strategy should be determined carefully even for small HCC when they appear hypointense on the ADC map.