Abnormal vasculature of the liver in thoracopagus twins: case report.

Each of the two minimally united livers of thoracopagus conjoined twins occupied an epigastrium in opposite aspects of the conjoined abdomen, straddling the plane of conjunction, instead of being located beneath the domes of the diaphragm. Whereas the hepatic artery and portal vein of the right twin supplied only the larger "anterior" liver, the same vessels in the left twin divided to provide blood for both the "anterior" and the "posterior" liver. Thus the "posterior" liver had only one porta hepatis while the "anterior" liver had two. In addition, the hepatic veins of both ectopic livers were found to drain into the inferior vena cava of only the left twin. All of these anomalies have been reported, albeit rarely, among 477 cases of thoracopagus and omphalopagus twins recently reviewed. A theory explaining the abnormal embryology of the liver is proposed.