ABSTRACT. The purpose of this pictorial review is to understand the embryological basis of the development of congenital hepatic vascular shunts and to review the multimodality imaging appearances of congenital and acquired hepatic vascular shunts. Hepatic vascular shunts are commonly seen in imaging. Familiarity with their characteristic appearances is important in order to accurately characterise these shunts and diagnose the underlying disorders. Intrahepatic vascular shunts are common; all intrahepatic vessels are associated with the formation of shunts. These include arterioportal (AP), portosystemic and arteriosystemic venous shunts. Rarely, systemic venous (i.e. hepatic vein to hepatic vein) shunts and portal-to-portal communications are seen [1]. The unique dual blood supply of the liver (approximately 75% portal venous and 25% arterial) means there is a compensatory relationship between the two sources. When vascular compromise occurs, it causes a macroscopic opening of the shunts between the hepatic arteries, the portal veins and the hepatic veins through physiological anastomoses, which become abnormally enlarged [1][2][3]. The purpose of this pictorial review is to illustrate the imaging appearances of hepatic vascular shunts on multidetector CT (MDCT) with sonographic and conventional angiographic correlation.
EmbryologyIn the fifth week of intrauterine life, there are three major paired veins in the abdomen: the vitelline or omphalomesenteric veins, the umbilical veins and the cardinal veins. The vitelline veins form the hepatic sinusoids. The left vitelline vein subsequently involutes and the blood is diverted into the right vitelline vein, which enlarges and forms the hepatocardiac portion of the inferior vena cava (IVC). Derivatives of the vitelline veins also form the hepatic and portal vein. The entire right umbilical vein and a portion of the left umbilical vein also degenerate. The persistent portion of the left umbilical vein connects to the right vitelline vein via the ductus venosus (Figure 1). The hepatic artery arises from the aorta and follows the mesentery [4,5].In antenatal circulation, oxygenated blood from the placenta returns to the foetus via the umbilical vein and flows through the ductus venosus into the IVC (Figure 2a). At birth, there is functional closure of the umbilical arteries, veins and the ductus venosus. Following atrophy, these form the medial umbilical ligaments, the ligamentum teres and the ligamentum venosum, respectively. Post-natal anatomy consists of inflow into the liver through the hepatic artery and portal vein, with the outflow through the hepatic veins (Figure 2b) [5].There is potential for intrahepatic shunts to develop when the ductus venosus remains patent, from failure of right upper vitelline vein regression, from a varix of the portal vein connecting to the hepatic/systemic venous circulation, from focal persistence of the most superior aspect of the vitelline veins or from arteriovenous malformations or neoplasms [6,7].