To investigate the influence of the cellular differentiation, the tumor size and the hepatic background on the washout of hepatocellular carcinoma (HCC) in contrast-enhanced ultrasound (CEUS).

All 403 cases of single HCC with arterial hyperenhancement (homogeneous or heterogeneous) who underwent CEUS examination in Southwest Hospital Affiliated to Third Military Medical University and were pathologically demonstrated as HCC by surgery or needle biopsy from January 2005 to June 2015 were retrospectively enrolled. Four washout patterns were classified according to the start time of washout: washout in arterial phase, washout in portal phase, washout in delayed phase and no washout. According to the cellular differentiation, the patients were grouped as well differentiated HCCs (n=115), moderately differentiated HCCs (n=156) and poorly differentiated HCCs (n=132). Based on the tumor size measured by ultrasound, the patients were divided into three groups: ≤3 cm (n=116), 3.1-5 cm (n=154) and >5 cm (n=133). On the basis of pathology, the background of liver were divided into cirrhosis (n=239) and non-cirrhosis (n=164). R×C table χ² test was used to analyze the proportion of different washout patterns among different cellular differentiation groups or different tumor size groups, and Pearson χ² test was used in the further two-two comparison among groups. Pearson χ² test was used to analyze the percentage of four washout patterns between cirrhosis and non-cirrhosis groups.

Of 403 cases, the percentage of initial washout occurring in arterial phase was not significantly different among different cellular differentiation HCCs. Well differentiated HCCs had significantly lower percentage of washout firstly emerging in portal phase and significantly higher percentage of washout firstly emerging in delayed phase or no washout when compared with moderately or poorly differentiated HCCs (portal phase: χ²=10.358 and 47.398, both P< 0.01; delayed phase: χ²=5.134, P<0.05, χ²=13.069, P<0.01; no washout: χ²=8.669 and 25.899, both P<0.05). The percentage of washout firstly occurring in portal phase of moderate differentiation lesions was significantly lower and the percentage of no washout of moderate differentiation lesions was significantly higher when compared with poor differentiation lesions respectively (portal phase: χ²=8.847; no washout: χ²=7.396; both P<0.01), while the percentage of washout firstly occurring in delayed phase was not statistically significant. There were no significant differences for the percentage of different washout patterns among the three groups of various size. The percentage of different washout patterns was not statistically different between cirrhosis and non-cirrhosis groups.

The tumor size and the background of liver did not influence the washout of HCC on CEUS. The percentage of different washout patterns differs significantly among different cellular differentiation lesions. Most well differentiated HCC displayed late washout or non-washout. So extended observation is necessary as late washout or sustained enhancement usually occur in most well differentiated HCCs. CEUS is useful for the diagnosis and classification of HCCs.