The caudate lobe of the liver: implications of embryology and anatomy for surgery.

The anatomy of the caudate lobe has technical and possibly oncologic implications for surgeons. The complex anatomy of the lobe is clarified by embryologic and anatomic analysis. This posterior sector is embryonically and anatomically independent of the right and left liver and the main portal fissure. The caudate lobe represents the only part of the liver that is in contact with the vena cava, except at the entrance of the main hepatic veins into the vena cava, and provides an anastomosis between the hepatic veins and vena cava. The entire caudate lobe is a single anatomic segment that is defined by the presence of portal venous and hepatic arterial branches, which supply the lobe, draining biliary ducts, and hepatic veins. Because no separate veins, arteries, or ducts can be defined for the right paracaval portion of the posterior liver and because pedicles cross the proposed division between the right and left caudate, the concept of segment IX is abandoned. The significance of caudate anatomy is reflected in the increase in the frequency and safety of major hepatic resection for primary and metastatic tumors in the liver. Right hepatic lobectomy routinely involves resection of the right portion of the caudate lobe (C. Couinaud, unpublished data, 1999). In the case of hilar bile duct cancer, which may extend into the dorsal ducts (especially the right lateral duct), partial or total caudate lobectomy is often necessary for complete extirpation of the tumor. Isolated caudate lobectomy can be performed for hepatocellular carcinoma that arises in the caudate lobe or for other tumors that arise in the lobe. The caudate lobe can be resected as part of the donor liver in preparation for a living related donor transplantation. Knowledge of the surgical anatomy of the caudate lobe is an essential part of the repertoire for surgeons who perform liver transplants or treat hepatobiliary cancer.