Anatomical variations of the origin of the segment 4 hepatic artery and their clinical implications.

The threat of ischemic complications following massive resection, especially in living donor hepatectomy or split liver transplantation, has been haunting surgeons for many years. Postmortem dissections of 62 livers were performed to investigate anatomical variations of the principal artery for segment 4 (A4). The origin of A4 was examined separately in the liver with (n = 46) or without (n = 16) an aberrant left hepatic artery (abLHA). A4s were found to be extrahepatic or intrahepatic branches of the right hepatic artery (RHA), left hepatic artery, or proper hepatic artery and were categorized into 4 different types according to their origins. The RHA type, originating from the RHA or right anterior hepatic artery (RAHA), was the most common pattern in our series. The A4 roots had a strong tendency of stemming from the RHA (n = 12) even in the livers with abLHA (n = 16). Among the RHA-type A4s, the A4 arising from RAHA (n = 2) is supposed to be the most dangerous variant because it can cause an ischemic change in the remaining part of the liver after right hepatectomy. In conclusion, in the era of living donor liver transplantation, paying particular attention to the point of origin of A4 is a prerequisite, especially when the lateral section is relatively small. Arterial injuries to A4 during split liver transplantation may also increase the risk of hepatic artery thrombosis and ischemic cholangiopathy.