Small hypervascular hepatocellular carcinomas: value of "washout" on gadolinium-enhanced dynamic MR imaging compared to superparamagnetic iron oxide-enhanced imaging.

The aim of this study was to retrospectively compare the value of "washout" on dynamic MR imaging with superparamagnetic iron oxide (SPIO)-enhanced imaging features of small hepatocellular carcinoma (HCC). A total of 74 small (5-30 mm) hypervascular HCCs in 42 cirrhotic patients who underwent double contrast material-enhanced MR imaging were evaluated to determine the presence of washout in the portal or equilibrium phase of gadolinium-enhanced dynamic imaging and decreased uptake of SPIO on T2*-weighted imaging. HCCs were verified histologically (n = 13) or by serial follow-up imaging studies (n = 61). According to the size of the lesions, 27 vs. 73% (<10 mm, n = 15; P = 0.016 on McNemar test), 39 vs. 79% (10-14 mm, n = 28; P = 0.002), 50 vs. 93% (15-20 mm, n = 14; P = 0.031), and 82 vs. 100% (>20 mm, n = 17; P = 0.250) of the lesions showed washout vs. decreased SPIO accumulation respectively. The larger the lesion, the higher the prevalence of washout or decreased SPIO uptake (P = 0.004 or P = 0.036, respectively, on Mantel-Haenszel test). In many small hypervascular HCCs up to 2 cm, SPIO-enhanced MR imaging offers essential information for early diagnosis in the absence of washout on dynamic imaging.