CT Imaging of early hepatocellular carcinoma and the natural outcome of hypoattenuating nodular lesions in chronic liver disease.

Background: The Liver Cancer Study Group of Japan has designated early hepatocellular carcinoma (HCC) a clinically early-stage HCC corresponding to a high-grade dysplastic nodule as proposed by the International Working Party.

Methods: The majority of resected early HCCs were demonstrated as having hypo- or isoattenuation in the arterial and delayed phases of dynamic CT.

Results: Only 5% of early HCCs were hyperattenuated on dynamic CT, whereas 94% of advanced small HCC were hyperattenuated. CT arterial portography (CTAP) showed that 66% of early HCCs were hypo- and 34% were isoattenuated. CT hepatic arteriography (CTHA) demonstrated that 55% of them were hypo-, 30% were iso- and the remaining 15% were hyperattenuated.

Conclusions: These findings suggest that most early HCCs receive equal or decreased blood supply from both portal and arterial blood flow compared with surrounding hepatic parenchyma. In contrast, 97% of small advanced HCCs were hypoattenuated on CTAP, and 93% were hyperattenuated on CTHA. For nodule-in-nodule type HCC, the central portion of the lesion was hyperattenuating and the peripheral portion was hypoattenuating in the arterial phase of dynamic CT, and both areas became hypoattenuated in the delayed phase. Sixty hypoattenuating nodular lesions in chronic liver disease were followed periodically with helical CT. Thirty-six (60%) of them developed to the hyperattenuating type (attenuation conversion), 21 were unchanged, and 3 disappeared spontaneously. The hyper-in-hypo-attenuating lesions showed rapid progression to entirely enhanced lesions, i.e. overt HCC. Dynamic CT is recommended as one of the low-invasive imaging modalities to follow the hypoattenuating nodules and to determine the optimal treatment with careful attention being given to intratumoral attenuation conversion.