[Dorsal sector of the liver].

The dorsal sector extends in front and to the sides of the inferior vena cava, separating the caval axis from the main liver (excepting superiorly the entrance of the main hepatic veins into the vena cava). The two elements, dorsal sector and retro-hepatic portion of the vena cava, actually make a single unit. It is made of two segments: left (segment I) larger than the Spieghel lobe, right (segment IX) incorporated in the posterior surface of the right liver. The "caudate process" is not a peculiar element: it is nothing else than the inferior margin of segment IX: the breadth gives information on the size of segment IX. The dorsal sector is the midportion of the posterior liver, it is absolutely independent of the right and left livers separated by the main portal fissure. Portal pedicles are numerous and ascendant, they arise from the posterior margin of the transverse portal arch (from right to left: segment VII vein, right lateral vein, right portal vein, left portal vein, segment II vein). The size of the dorsal sector is variable, and can be appreciated by an antero-posterior index. A voluminous sector may be a problem for the surgeon. Segment IX can be divided in three subsegments: IXb under the interval between the right superior hepatic vein and the middle hepatic vein (longer branches can ascend and supply a small portion of the upper surface in front of the vena cava), IXc under the very broad right superior vein, and posteriorly IXd, linked to segment VII. Only segment I and subsegment IXb receive branches from the right and from the left livers. Hepatic veins enter directly the caval axis, some enter the main hepatic veins. The dorsal sector is a large anastomosis between efferent veins and the vena cava. Anteriorly segment I is in contact with segment IV but also with segment VIII, subsegments IXb and IXc with segment VIII and IXd with segment VII. The fissural limit is difficult to locate. Posteriorly division of the triangular and coronary ligaments, section of the dorsal hepatic veins, the right middle and inferior veins allow separation of the liver from the posterior abdominal wall and the inferior vena cava, so the surgeon can reach the dorsal sector. A remarkable error has been commited when the main hepatectomies were described: the dorsal sector was not known and the caudate lobe was considered as a part of the left liver. Actually the dorsal liver is a separate entity covering the inferior vena cava which has no connexion with the main liver; when the main portal fissure is opened up to the anterior surface of the vena cava, the dorsal sector is opened vertically. Interruption of the pedicles must also be considered. For example, in a left hepatectomy, the left portal pedicle is divided, all the left branches for subsegment IXb (which will be preserved) are interrupted; but the left branches from the right portal pedicle are not interrupted and will bleed when the dorsal sector is divided. When splitting the liver for transplantation, some difficulties can occur, especially with the right transplant. A main practical interest is the possible propagation to the dorsal ducts of hilar carcinoma.