ročník 11,2003 č.4Kongres
Surgical anatomy and its impact to liver surgery
Jaeck, D., Oussoultzoglou, E.Centre de Chirurgie Viscérale et de Transplantation
Hôpital Universitaire de Hautepierre, Strasbourg Cedex
Nomenclature of liver segmentsFor a long time the scientific community used several terminologies sometimes confusing concerning hepatic anatomy. Indeed, the North American surgeons used the classification of liver segments described by Healey, while the Couinaud's classification was used in Europe and in Japan. Recently, a new terminology called the Brisbane 2000 Terminology of Liver Anatomy and Resections has been unanimously recommended and accepted by the scientific committee of the International Hepato-Pancreato-Biliary Association (IHPBA) in order to resolve the existing confusion (1).
General considerationsThe main technical procedures required in order to achieve a safe hepatectomy include adequate mobilization of the liver, control of supra and infrahepatic inferior vena cava and control of the main inflow and outflow liver vessels. Meticulous vessels ligation during parenchymatous transection represented the basic maneuver for liver resection reducing vascular and biliary complications. However, some differences between liver resection for a tumoral disease and liver resection for obtaining a graft (living donor and split liver) exists. In this latter procedure several differences exist. First, transection of the liver parenchyma must be performed before ligation or clamping of the glissonian vessels in order to minimize normothermic ischemia and to preserve graft viability (2). Second, the vasculars pedicles and biliary ducts must be ligated on both sides during parenchymatous transection (3). Third, both part of the liver must be carefully retracted during parenchymatous transection to avoid any damage of the graft. The emergence of split and living donor liver transplantation has necessitated reevaluation of liver anatomy. Moreover, most of the early post-operative biliary and vascular complications can be attributed to technical problems and failure to recognize anatomical abnormalities. Therefore, a wide range of perioperative investigations such as CT or MRI cholangiographies and angiographies and intraoperative ultrasonography are routinely used to map out the vascular and biliary anatomy and to draw the line of liver parenchymatous transection.
Liver ligamentous attachmentsWhile basic maneuver includes liver mobilization by sectionning the ligamentous attachements of the liver, these structures could be very helpful in palliating liver ischemia with the development of collateral circulation. For instance, in case of Klatskin tumor with arterial involvement, arterial supply delivered through the ligamentous attachements can be of great interest. In addition, reconstruction of these ligaments avoids twisting of the left liver after right hepatectomy which could lead to outflow obstruction. Intraoperative Doppler ultrasound after right or extended right hepatectomy is useful in assessing the adequacy of vascular inflow and outflow ; it helps to determine the optimal position in which to anchor the liver. Finally, the absence of liver mobilization has many theoretical advantages. It may limit tumor cells dissemination and prevent compression of the remnant liver which alters liver inflow and outflow. A new strategy for major hepatectomy without liver mobilization for large tumors has been described (2,3) and completed with the liver « hanging maneuver » (4).
Portal veinThe vascularization of the hepatocytes is mainly provided by the portal vein flow and second by the hepatic artery. In order to decrease intraoperative blood loss during a hepatectomy the most common method consists in a Pringle maneuver. However, this method results in ischemia of the whole liver. Other techniques are used in order to control selectively the vascular inflow of the liver and to preserve the blood supply of the future remnant liver. Such selective techniques reduce period of warm ischemia and minimize reperfusion hepatic injury optimizing the function of the remnant liver. During living liver transplantation, failure to recognize portal vein abnormalities can partially devascularize the corresponding segments. This can be observed either in the presence of a non-division of the portal trunk with absence of a separate left main portal vein, or in the presence of a trifurcation of the portal vein. Vascular reconstruction with or without grafts interposition can be performed to restore vascular continuity. In some cases division of the segment I portal branches in the donor may be necessary to gain adequate length for anastomosis.
Hepatic veinsAnother way to reduce intraoperative blood loss is to control the hepatic veins. Low central venous pressure is necessary to control bleeding from the hepatic veins. Short inferior right hepatic veins drain the posterior sector of the liver (segment VI and VII) and go directly into the retrohepatic vena cava ; while the segment I drain predominantly on the left by a 1 to more than 20 venules attaching the caudate lobe to the retrohepatic inferior vena cava. Accessory inferior hepatic veins can sometimes be relatively large allowing an adequate outflow of the segments which avoids outflow congestion in case of resection or ligation of the main hepatic veins (5). Therefore, large accessory hepatic vein encountered during dissection of the anterior wall of the retrohepatic vena cava should be preserved until the extent of hepatectomy is decided. In liver transplantation, particularly in living donor between adults using right liver graft, these large accessory hepatic vein must be implanted separately into the inferior vena cava of the recipient. During bisegmentectomy II and III, tributaries of the left and middle hepatic vein draining the corresponding areas are almost always encountered and sectionned without compromizing the outflow of the segment IV. In addition, the presence of a transverse segment II vein allows resection of that segment in order to perform a monosegment liver transplantation and to overcome a size discrepency between donor and recipient. It allows also to perform segmentectomy II with keeping segment III with good outflow. The technique of split liver liver transection performed on the right of the middle hepatic vein in order to create two grafts of adequate and approximately equal mass for two adult recipients was criticized as it provokes interruption of the venous outflow of segments V and VIII. Subsequently congestion and bleeding from the cut surface of the right liver lobe may occur affecting the functional volume of the graft. The same situation is observed in adult living donor transplantation when the right liver is harvested without the middle hepatic vein. In case of a small right hepatic vein, the middle hepatic vein holds the key to right liver living donation as it provides the sole drainage of the segments V and VIII. In the presence of an adequate vascular inflow and a satisfactory functioning liver mass this anatomical abnormality should no longer be considered as a contraindication to right liver living donation. Indeed, reconstruction of outflow with venous grafts can be performed.
Inferior vena cavaThe anterior wall of the retrohepatic vena cava constitutes an important dissection plane. Mobilization of the liver from the anterior wall of the vena cava facilitates the dissection and selective control of the main hepatic veins just before they enter the vena cava. These selective vascular controls allow major liver resection without interruption of the caval flow and avoid hemodynamic instability (6). Prosthetic replacement of the vena cava has been also performed with or without reimplanation of the main hepatic veins according to the cranial extent of the vena cava resection. In split liver transplantation, it is preferable to keep the vena cava with the right liver graft in the presence of large accessory right hepatic veins. Alternative approaches include opening the inferior vena cava longitudinally to take a patch containing all tributary veins and performing a cavoplasty in the recipient.
Hepatic arteryEach artery should be preserved as it is an end artery without anastomosis inside the liver and each artery has its specific areas of blood supply. Moreover arterial supply is essential for bile duct vascularization and viability. In case of arterial thrombosis occuring in the early phase after liver transplantation serious complications may develop in the biliary duct with risk of necrosis. Most frequently segment IV receives its blood supply from the left hepatic artery. However, sometimes the entire blood supply comes from a branch of the right hepatic artery which crosses through the Cantlie's line. Non recognition of this abnormality may result in a compromise of the blood supply of segment IV with associated postoperative bile leak. This situation can be overcome by a careful identification and preservation of this branch during the dissection of the hepatoduodenal ligament as these vessels may have an extrahepatic course at the hilum. The right hepatic artery should be divided beyond the origin of the segment IV artery. These abnormalities do not affect liver resection for localized tumor as pedicle control and ligation are performed during liver parenchymatous transection. However, recognition of such abnormality is essential in living donor liver transplantation. Complex microsurgical arterial reconstruction has recently been described (7). Preoperative CT or MRI angiography should be routinely performed to detect these arterial abnormalities.
Biliary ductIn contrast with liver parenchyma, blood supply for the bile ducts is only provided by the hepatic artery. Therefore, excellent arterial reconstruction is required to allow a satisfactory blood supply for the bile ducts and to reduce the risk of necrosis or ischemic stricture of the intra- or extra-hepatic bile ducts. Skeletonizing of the bile ducts at the hilum should be avoided. In addition, clamping of the extrahepatic bile duct during the Pringle maneuver should also be avoided. Dissection at the hilum should be minimized not only to prevent injury of abnormal ducts but also to preserve the underlying vascular plexus which contributes to the arterial blood supply of the intra- and extra-hepatic bile ducts. These considerations are also important to perform successfully bilio-enteric anastomoses and to avoid biliary fistula or stricture of hepatico-jejunal anstomoses. The bile duct of segment I drains into the confluence of the right and the left hepatic duct. Therefore, when a resection of the intrahepatic biliary confluence is decided a « en bloc » segmentectomy I should be performed to avoid biliary leakage. It is also necessary in case of Klatskin tumor in order to eradicate tumoral invasion of bile ducts of the segment I. Abnormal drainage of segment IV duct into the right hepatic duct, may lead to bile leak in both the donor and the recipient if the liver is splitted centrally for two adults. Bile leak can also occur during a left hepatectomy. This complication occurs when an associated abnormal anterior or posterior right hepatic duct drains into the left bile duct. The incidence of such accidents during conventional parenchymatous transection can be minimized by dividing the left hepatic duct as close to the parenchymal surface as possible, far away from any abnormal right segmental duct draining into the left duct.
ConclusionIn conclusion a comprehensive understanding of surgical anatomy of the liver is mandatory to improve and maintain the excellent results of liver surgery and of liver transplantation. Despite perioperative investigations, not all vascular and biliary anomalies can be accurately demonstrated before surgery and some of them may be diagnosed only when they are looked for during the operative procedure if the surgeon has a good knowledge of these abnormalities and anatomical variations.
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Address for correspondance :Professeur Daniel JAECK, MD, PhD, FRCS
Centre de Chirurgie Viscérale et de Transplantation
Hôpital Universitaire de Hautepierre
Avenue Moliere, 67098 Strasbourg Cedex, France
Tel : + 33 3 88 12 72 58, Fax : + 33 3 88 12 72 86