Retraction Note to: Contrast-enhanced ultrasound appearances of enhancement patterns of intrahepatic cholangiocarcinoma: correlation with pathological findings.

The aim of this study was to investigate the correlation between enhancement patterns of intrahepatic cholangiocarcinoma (ICC) on contrast-enhanced ultrasound (CEUS) and pathological findings. The CEUS enhancement patterns of 40 pathologically proven ICC lesions were retrospectively analysed. Pathologically, the degree of tumour cell and fibrosis distribution in the lesion was semi-quantitatively evaluated. Four enhancement patterns were observed in the arterial phase for 32 mass-forming ICCs: peripheral rim-like hyperenhancement (n = 19); heterogeneous hyperenhancement (n = 6); homogeneous hyperenhancement (n = 3); and heterogeneous hypo-enhancement (n = 4). Among the four enhancement patterns, the differences in tumour cell distribution were statistically significant (p < 0.05). The hyperenhancing area on CEUS corresponded to more tumour cells for mass-forming ICCs. Heterogeneous hyperenhancement (n = 2) and heterogeneous hypo-enhancement (n = 2) were observed in the arterial phase for four periductal-infiltrating ICCs. In this subtype, fibrosis was more commonly found in the lesions. Heterogeneous hyperenhancement (n = 1) and homogeneous hyperenhancement (n = 3) were observed in the arterial phase for four intraductal-growing ICCs. This subtype tended to have abundant tumour cells. The CEUS findings of ICC relate to the degree of carcinoma cell proliferation at pathological examination. Hyperenhancing areas in the tumour always indicated increased density of cancer cells.