The isolated artery: An intrahepatic arterial pathway that can bypass the lobular parenchyma in mammalian livers

Abstract

Controversy persists concerning the distribution of intrahepatic arterial termination. Apart from nourishing structures in the portal tract, several authors have suggested arterial supply to some isolated vascular beds that bypass the parenchyma, but this was not verified morphologically. In the present study, the existence of an isolated hepatic artery unaccompanied by a portal vein or a bile duct was shown in livers of pigs and other mammals including the dog, seal, ox, horse, and man. After colored media injection, liver blocks were sampled near the hepatic capsule and hepatic vein and subject to histologic assessment. The hepatic artery dissociated from superficial portal tract, ramified, and anastomosed extensively, forming a capsular plexus that drained at places into peripheral sinusoids in which resistive structural elaborations were observed. The artery also dissociated and fed an intramural plexus (vasa vasorum) of hepatic veins. This was collected into a vessel that penetrated the intima into the vein's lumen. In smaller sublobular veins, the plexus emptied into adjacent sinusoids; in central veins, the plexus was poorly developed. In canine and phocine livers, which have a special throttling musculature in sublobular veins, the isolated arterioles were numerous; in bovine and equine livers, which have a thick fibrous investment, the capsular plexus was welldeveloped. Occurrence of the isolated artery also was confirmed in the human but not in the rodent liver. In conclusion, the isolated artery is responsible for isolated vascular beds, in which the transintimal pathway can bypass the lobular sinusoids. (HEPATOLOGY 2000;31:269-279.)There is no definite consensus concerning the distribution and functions of the hepatic artery. Intrahepatic termination of the arteria hepatica propria has been a controversial issue for more than a century. 1 Review of the literature shows that the subject became controversial in 1866, when Chrzonszczewsky, 2 with his classic experiments of selective ligation and injection, observed that branches of the hepatic artery penetrated into the depth of the lobule, and concluded subsequently that the artery nourished the central half of the liver lobule, whereas the portal vein supplied the peripheral half. One hundred years later, in 1966, not only were the statements unsupported, but also many studies extended the controversy about the anatomy 3-7 and physiology 8,9 of intrahepatic arterial distribution. As a result, the clinical and pathological significance of the hepatic artery has remained ill defined, because how the vessel ramifies in the liver has not been accurately described. 10 Microscopic terminations of the hepatic artery are classified into 2 categories, within the portal tract and outside of the portal tract. The former is associated with the formation of periductal plexus and arterioportal anastomosis, 11 whereas the latter is typically related to the distribution of intralobular arterioles. 12 It is the second category that has been most argued. From time to t...

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