Intrahepatic metastases in hepatocellular carcinoma: the role of the portal vein as an efferent vessel.

The mechanism and pathogenesis of the high frequency of intrahepatic metastasis in hepatocellular carcinoma (HCC) has not yet been elucidated. Two hundred and thirty one tumors (< or = 5 cm in diameter) of resected specimens of HCC were examined for the relationship between mode of tumor spread and tumor size. Efferent vessels in HCC were identified by direct injection of radiopaque material into the tumor in 23 resected liver specimens selected at random from the 231 tumors. The most frequent site for tumor spread in HCC was capsular invasion followed by extracapsular invasion, vascular invasion, and finally intrahepatic metastasis. There was a strong statistical correlation between the presence of intrahepatic metastasis and the frequency of vascular invasion (correlation coefficient = 0.998). Radiopaque material injected directly into 23 resected tumors entered only the portal vein in 17 tumors and into both the portal and hepatic veins in six tumors. In all eight patients with unresectable lesions, radiopaque media injected percutaneously into tumor nodules flowed only into the portal vein. These findings suggest that tumor spread in HCC progresses from capsular invasion to intrahepatic invasion and that the portal vein may act as an efferent tumor vessel.