Surgical Anatomy of the Liver

Surgical Anatomy of the Liver

Symposium on Hepatic Surgery Surgical Anatomy of the liver Paul A. Kennedy, M.D.,'~ and Gordon F. Madding, M.D. t Little is said concerning the i...

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Symposium on Hepatic Surgery

Surgical Anatomy of the liver

Paul A. Kennedy,

M.D.,'~

and Gordon F. Madding, M.D. t

Little is said concerning the intrahepatic anatomic arrangements in descriptions of the gross anatomy of the liver. For the most part, reference is made to the surface markings and regional relationships. The division of the liver into two lobes by the falciform ligament has until recently been accepted by the authors of many texts and the studies ofRex,16 Hjortsjo,9 Bilbey,2 Segall,17 McIndoe and Counseller,13 Elias and Petty,4 Goldsmith and Woodburne,5 and Healey and co-workers6-s have been ignored until recently. Surgical interest in resections of the liver and knowledgeable care in cases of liver trauma have led to a more careful definition of the intrahepatic arrangements. A working knowledge of the prevailing patterns as well as anomalous arrangements is essential not only for carrying out such surgical procedures as lobectomy but also in the surgical care of the injured liver. It is the purpose of this article to bring together the facts concerning regional anatomy of the liver as well as intrahepatic arrangements. This will obviate complications associated with liver trauma and will also aid in conserving functioning liver tissue. The liver is the largest organ in the body, having an average weight in the adult of approximately 3 lb. The average transverse diameter is approximately 20 to 23 cm. The greatest measurement at the midpoint of the right lobe is 15 to 17 cm. The greatest anteroposterior diameter on a level with the upper pole of the right kidney is approximately 10 to 12.5 cm. The liver assumes the shape of a pyramid or a wedge with the base directed to the right and the apex or thin leading edge toward the left, thus presenting three major surfaces. A sharp, well defined margin is formed by the meeting of the superior and inferior surfaces, whereas the remaining margins are rounded. The entire right hypochondrium is occupied by the liver which extends to the left across the midline where it comes into intimate relation with the anterior surface of the stomach, left kidney, and spleen. "Assistant Clinical Professor of Surgery, Stanford University School of Medicine, Stanford, California t Associate Clinical Professor of Surgery, University of California, San Francisco, School of Medicine; Associate in Surgery, Stanford University School of Medicine, Stanford, California

Surgical Clinics of North America-Vol. 57, No.2, April 1977

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PERITONEAL ATTACHMENTS (LIGAMENTOUS)' The liver is fixed in position by a number of ligamentous structures which are simply deflections of parietal peritoneum onto the liver surface. Intraabdominal and some negative pressure between the diaphragm and the superior surface of the liver aid in holding the liver in place. The falciform ligament forms a T posteriorly with the anterior leaf of the coronary ligament and with the smaller left triangular ligament and the more extensive right triangular ligament (Fig. 1). The entrance of the obliterated umbilical vein along the free margin of the falciform ligament is commonly and erroneously used to distinguish the right from the left lobe. 18 The falciform ligament in reality is a surface marking serving to delineate superiorly and anteriorly the junction of the medial and lateral segments of the left lobe ofthe liver. This line of division is well to the left of the plane separating the right and left lobes. The bare area of the liver lies between the anterior or upper layer of the coronary ligament and the posterior or lower layer in which the inferior vena cava and hepatic veins are located. At the extreme right and left the two leaves of the coronary ligament join laterally to form the triangular ligaments. Figure 1 shows the inferior surface of the liver. A line drawn through the fossa for the vena cava posteriorly and the fossa for the gallbladder anteriorly represents the main fissure dividing the liver into right and left lobes. A line drawn through the fissures for the ligamen-

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Figure 1. The three surfaces of the liver are shown. A, The anterior view with the interlobar fissure marked by the line x-x and the left segmental fissure marked by the line y-y. B, Posterior view, showing the same fissures. C, Inferior view.

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tum venosum and the ligamentum teres marks the fissure between the medial and lateral segments of the left lobe. Most of the medial segment of the left lobe consists of the quadrate lobe. The caudate lobe, however, because of its bilateral blood supply and drainage, is in reality a separate lobe belonging neither to the right nor to the left side. The liver hilum is centrally located on the inferior surface and is therefore protected, which explains the less frequent injuries in this area. The somewhat protected position of this vital area does afford some immunity to blunt trauma but less to deep penetrating wounds. Wounds involving the hilum are usually of a greater magnitude and are frequently lethal. Arborization of the portal system, the hepatic artery, and bile ducts, as shown in corrosion casts, takes place toward the periphery and toward the superior surface in such a manner that the vessels and ducts rapidly diminish in size. In the majority of our casts, the hilar structures up to the second division could be covered by an area equal to that of a silver dollar.

SURFACE MARKINGS OF THE LIVER (CUTANEOUS REFERENCE) Figure 2 shows the cutaneous reference of the liver anteriorly, posteriorly, and from the lateral aspect. The dome of the right lobe reaches approximately to the level of the fifth rib or fourth interspace in the Inidclavicular line. This level varies with respiratory excursion. In the midline the upper reference is at the junction of the body ofthe sternum at the xiphoid cartilage. The upper limit of the left lobe is marked by continuing this line laterally from this point to the left fifth costal cartilage 5 cm from the midline. The leading edge of the liver on the right side conforms

Figure 2. Skin surface projections of the liver; a, anteroposterior; b, posteroanterior; c, right lateral.

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to the costal margin. A varying amount of liver would normally be felt in the epigastric space depending on the configuration of the costal margin. A working knowledge ofthe surface projection of the liver is important in appraising accurately the path of a missile or wounding agent.

INTRAHEPATIC ARCHITECTURE A plane or fissure extending from the gallbladder fossa below to the fossa of the inferior vena cava above divides the liver into two surgical lobes. The angle of this plane is about 35 degrees with the vertical plane and 20 degrees with the sagittal plane opening anteriorly.9 This "main boundary" fissure or "Hauptgrenzspalte" of Hjortsjo is readily demonstrated in vinyl acetate casts in which the hepatic veins have not been injected. There are no surface markings to indicate the location of this fissure but it is clearly demonstrated in Figure 3. Corrosion casts of the liver in which the portal system, the hepatic artery, and bile ducts have been injected show very clearly the main boundary fissure between the two lobes as well as the fissure between the anterior and posterior segment of the right lobe. Subsegments as well are clearly demonstrated by corrosion casts. It is difficult to demonstrate in corrosion casts the crossing of the lobar or segmental fissures by branches of either the hepatic artery or portal vein but it does occur. The left lobe is similarly divided into two segments, a medial and a lateral, by a plane that is commonly used to designate the "anatomic" lobes. The falciform ligament marks its anterosuperior visceral surface projection from which line the plane is directed medially and inferiorly, reaching only to the umbilical trunk of the left portal vein (Fig. 3C). It does

Figure 3. Corrosion cast of the liver in which the portal vein and hepatic arteries have been injected. The right segmental fissure (A), the lobar fissure (B), and the left segmental fissure (C) have been marked by plastic dividers. The plane of the left segmental fissure is directed medially and inferiorly, reaching only to the umbilical trunk of the left portal vein. It does not extend to the main boundary fissure.

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not extend to the main boundary fissure. The lobar fissure is shown in Figure 3B.

BLOOD SUPPLY OF THE LIVER The liver receives its blood from two sources, the hepatic artery (25 per cent) and the portal vein (75 per cent). Blood is returned to the vena cava by way of the hepatic veins. Michels 14 found the conventional textbook picture of the arterial supply to the liver in only 55 per cent of dissections. In 25 per cent of his cases the left gastric artery gave rise to the left hepatic artery, in half of which there was an additional left hepatic artery. In the other 50 per cent, only one left hepatic artery was present. In 17 per cent of Michels' 200 dissections the superior mesenteric artery gave rise to an additional right hepatic artery; in 12 per cent of the cases it gave rise to a right hepatic artery, which provided the entire blood supply to the right lobe. In Figure 4 six anomalous arrangements of the arterial blood supply to the liver are shown. Lander, Lyman, and Anson l l in 100 consecutive dissections found a variation from the normal in 15 per cent of cases. At times the blood supply of the liver may be furnished by an hepatic trunk derived from the superior mesenteric artery. There has been general agreement that hepatic arteries are end arteries with no anastomosis in the liver. 8 Michels 14 lists 26 possible collateral arterial pathways to the liver but states that because of the unpredictable origin of the blood supply of the liver, few, if any, of these collaterals can be relied upon. However, recent studies by Bengmark, Rosengren, and others 3 have shown that these collateral pathways are more important than at first thought. Rapid development of collateral vessels does occur following hepatic artery ligation by way of the phrenicoabdominal and intercostal arteries as well as by numerous small vessels in the region of the porta hepatis and in the area of the caudate lobe. 15 Segall 17 demonstrated numerous collaterals in the capsular folds at the hilum when one hepatic lobar arterial trunk was ligated. We were able to show a true crossover from the righ t 10 be to the left 10 be in only one specimen (Fig. 5), Healey and co-workers 8 demonstrated extrahepatic anastomoses between the right and left hepatic arteries in some 25 per cent of cases. These anastomoses were all subcapsular in position and small in caliber and were found in the following sites: in the umbilical fossa connecting the medial and lateral segmental arteries; in the region of the porta hepatis connecting the caudate lobe arteries; and between the caudate arteries and the posterior segmental artery to the right of the porta hepatis. Posthepatic artery ligation studies done either for control of massive bleeding associated with trauma or for treatment of metastatic tumors of the liver have shown the collateral pathways suggested by Michels 14 to be of great importance.

Hepatic Artery-Extrahepatic Distribution The common hepatic artery arises from the celiac axis and runs through the hepatoduodenalligament medial to the common hepatic duct

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Accessory LHA from LbA LGA

Figure 4. A, The replaced common hepatic artery (CHA) originating from the superior mesenteric artery (SMA). B, The replaced right hepatic artery (RHA) originating from the superior mesenteric artery. C, The accessory right hepatic artery originating from the superior mesenteric artery. D, The proximal bifurcation of the hepatic artery or the right and the left hepatic artery (LHA) originating separately from the celiac artery. E, The replaced left hepatic artery originating from the left gastric artery (LGA). F, The accessory left hepatic artery originating from the left gastric artery. The middle hepatic artery (MHA) and the splenic artery (Sp. A) are also identified. (Modified from Netter, F. H.: The CIBA Collection of Medical Illustrations, 1957.)

Figure 5. An arterial crossover from the right hepatic artery to the left hepatic artery is demonstrated: A, right hepatic artery; B, left hepatic artery; C, middle hepatic artery (supply to medial segment of the left lobe); D, crossover artery retouched for clarity.

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Figure 6. Intrahepatic arrangement of hepatic arteries and bile ducts. A, Hepatic arteries, shown in black: (1) hepatic artery, (2) right hepatic artery, (3) left hepatic artery, (4) right posterior segment, (5) right anterior segment, (6) left medial segment, (7) left lateral segment. B, Corresponding biliary ducts, shown in white. (Modified from Healey, J. E., Jr., Schroy, P. S., and Sorensen, R. J.: J. Int. Coll. Surg., 20:133, 1953.)

and anterior to the portal vein. It divides into two branches at any given point between the origin of the vessel and the porta hepatis (Fig. 6).14 When the division takes place near the porta hepatis it is not in line with lobar fissure but is situated to the left, resulting in a longer right hepatic artery. 8 In most instances the right hepatic artery enters the liver parenchyma posterior to the hepatic duct. In its course to the right it comes to lie below, but not usually in close relationship to, the right hepatic duct. The left hepatic artery trunk is considerably shorter than that of the right and almost immediately gives off segmental branches to the left lobe. As a rule, it is usually situated well below the hepatic duct. The left hepatic artery follows the pattern of branching of the hepatic duct in approximately 40 per cent of Healey's specimens; that is, the artery terminated by dividing into medial and lateral segmental branches. 8 What is referred to by some as a middle hepatic artery is in reality the left medial segmental artery. The right hepatic artery takes its origin from the proper hepatic to the left of the common hepatic duct and passes to the right behind this duct. It does not maintain a close relationship to the right biliary duct and terminates by dividing into an anterior and posterior segment. The first part of the anterior segment branch lies more inferior than its posterior counterpart and usually forms a loop close to the gallbladder fossa. The right hepatic artery gives rise to the cystic artery in half the specimens in which it was injected in Healey's studies, and in 18 cases it took origin from the anterior segment artery.8 In 25 per cent of Michels' dissections, the cystic artery had a dual origin.14

Left Hepatic Artery The medial and lateral segments of the left lobe are supplied by the left hepatic artery, a relatively short vessel that divides almost immediately into its terminal branches. Its oblique course extending from the inferior surface superiorly and laterally permits an almost complete resection of the medial segment of the left lobe with preservation of the lateral segment. 12 In the majority of cases the artery divides into medial and lateral segments and follows the prevailing branching ofthe portal vein and the hepatic ducts. 8 In 25 per cent of cases a major portion of the arterial supply to the left lobe (medial segment) is from the right hepatic artery.8

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Portal Vein The valveless portal vein is the scaffolding, in a sense, upon whiCh the liver is built and it returns blood to the liver from the mesenteric bed, the pancreas, and the spleen. It is formed by the junction of the superior mesenteric veins and the splenic vein anterior to the vena cava and posterior to the head and neck of the pancreas and emerges from behind the duodenum to course in the free fold of the gastrohepatic omentum. It measures approximately 7 to 8 cm in length and in the porta hepatis lies posterior to the common bile duct and the hepatic artery. It divides into a right and left trunk at the hilum of the liver. The left trunk is longer and morphologically less effective as a channel of blood flow. 4 The left portal vein has a transverse portion, which lies in the hilum, and an umbilical part, which lies in the left segmental fissure (Fig. 7A). The somewhat unfavorable circulatory pattern on the left side originates during the development of the organ, since a part of the umbilical vein has served from birth as the distal portion of the left trunk of the portal vein in which the entire blood flow has been reversed. 4 The transverse part of the left trunk is 2 to 3.5 cm in length. At this point, it bends in an anterolateral direction to form the umbilical portion, which immediately gives off a branch to the superior area of the lateral

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Figure 7. A, Intrahepatic branches of the portal vein: RPV, right portal vein; LPV, left portal vein; A, transverse portion; B, umbilical portion. B, The hepatic venous return, showing intralobar position of middle hepatic vein and intrasegmental portion of the right hepatic vein. (Modified from Healey, J. E., Jr.: Int. Coll. Surg., 22:546, 1954.)

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segment. Branches to the inferior area (medial and lateral segments) arise from the most distal portion of the pars umbilicus (Fig. 8). The umbilical portion lies in the anterior part of the left lobar segmental fissure, making it imperative that the line of resection for a lateral segmentectomy be made 1 to 2 cm lateral to the falciform ligament. The branches to the medial segment originate from the umbilical trunk as it runs in the left lobar segmental fissure. The right trunk of the portal vein measures approximately 2 to 3 cm in length and runs laterally from its point of origin to the right where it divides into an anterior and posterior segmental vein. 8 Considerable variation in the branching of its rami have been demonstrated, and in the studies of Elias and Petty 4 no two specimens were alike as far as rami of the right half of the liver were concerned. In two instances in our vinyl acetate casts, the portal branch to the right anterior segment originated in the transverse trunk on the left side. Hilar ligation in this instance for a left hepatic lobectomy would interrupt portal blood flow to a major portion of the right lobe. Although anastomoses between branches of the portal vein in normal livers are few, they do communicate in the sinusoids that are located in the territory common to two adjacent hepatic lobules. 4

Hepatic Veins The major portion of the venous return is by way of the right hepatic, middle hepatic, and the left hepatic veins (Fig. 7B). The posterior segment of the right lobe and a major portion ofthe superior aspect of the anterior segmen t of this lobe is drained by way of the right hepatic vein which is the largest of the three. The middle and left hepatic veins join to enter the vena cava as a single trunk but also may have separate but adjacent points of entry. The superior aspect of the medial segment ofthe left lobe and the inferior aspect of the anterior segment of the right lobe are drained

Figure 8. Vinyl acetate cast of the portal system, showing the left portal vein (a), the umbilical portion (b), and the portal vein proper (c) which marks the lobar fissure.

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by the middle hepatic vein. Thus, the main boundary fissure is crossed by the middle hepatic vein. The superior portion of the medial segment and the entire lateral segment of the left lobe are drained by the left hepatic vein. The caudate lobe is drained by two or more veins that enter the vena cava on its left side anteriorly. The posterior and lateral portions of the posterior segment of the right lobe are drained by several veins that join the vena cava at its right posterolateral aspect. The right superior vein may enter the vena cava directly but usually drains into the superior aspect of the right hepatic vein. The left superior vein enters directly into the vena cava and drains the area marked by the left triangular ligament. In exposing the esophageal hiatus this vein is occasionally torn when the left triangular ligament of the liver is dissected. Numerous anastomoses between hepatic veins have been reported. 4 These have been difficult to demonstrate in corrosion casts. Some general agreement exists that such communications do occur between the portal and hepatic venous systems in normal specimens. 4 The communication is between the afferent venule of the portal system and the sublobular hepatic veins. In specimens in which only the hepatic veins are injected, a segmental distribution of drainage is readily demonstrable (Fig. 9). These anatomic divisions, however, do not parallel the segmental arrangement of the portal system. The two systems interdigitate in such a way that when both are injected, no lobar or segmental planes are demonstrable. Figure 10 shows the relationship of the hepatic venous return to the portal vein, hepatic artery, and biliary system. The segmental pattern of distribution of the hepatic artery, portal vein, and bile ducts is completely obscured when the hepatic veins are also injected in the same specimen.

BILIARY DRAINAGE OF THE LIVER The pattern of biliary drainage follows very closely that of the hepatic artery and portal systems. There is little anatomic evidence that a functional anastomosis exists between the right and left lobes except

Figure 9. Vinyl acetate cast of the vena cava and hepatic veins. Right hepatic vein (a). middle hepatic vein (b), left hepatic vein (c), and the inferior vena cava (d). The left and middle hepatic veins can be seen joining to enter the vena cava as a common trunk.

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Figure 10. The hepatic venous return as shown runs almost perpendicular to the main branchings of the portal vein, hepatic artery, and biliary ducts. The umbilical portion of the portal vein in the left segmental fissure is clearly shown. (Redrawn from Elias, H., and Sherrick, J. C.: Morphology of the Liver. New York, Academic Press, 1969.)

across the junction of the right and left hepatic ducts in the porta hepatis. In injected specimens there appears to be no communication between the bile ducts of the anterior and posterior segments of the right lobe across the segmental fissure. In a small percentage of cases, bile ducts do appear to cross the left segmental fissure. 7 Ligation of a lobar or segmental biliary duct is not usually followed by jaundice; however, this may not be true of all forms of ductal obstruction at these levels. 19 The right hepatic duct measures approximately 9 mm in length and is formed by the union of the anterior and posterior segmental ducts near the porta hepatis. Seventy-two per cent of the corrosion casts in Healey's studies7 showed this arrangement to prevail. However, in 28 per cent, either the posterior or the anterior segment duct crossed the lobar fissure to drain into the left hepatic duct. Left lobectomy in such cases would interrupt drainage from either the anterior or the posterior segment of the right lobe. The lateral segment of the left lobe is drained by two segmental ducts, the more extensive inferior and the smaller superior, which j oin at the line of the segmental fissure. The medial segment drainage is considerably more variable. The drainage of the caudate lobe is also variable and drainage into both the right and left hepatic ductal system may occur. The left and right lobar ducts join in the transverse fissure to form the common hepatic duct. It varies in length from 1 to 5 cm, the average being 2.5 cm. Lander and co-workers l l showed that this arrangement prevailed in 97 per cent of their dissections. The cystic duct has a variable length, ranging from 0.5 to 4.5 cm, averaging approximately 2 cm. It joins the right side of the hepatic duct to form the common bile duct. l l There is considerable variation in the length of the common bile duct (2.0 to 7.0 cm); however, it is remarkably consistent in its course and arrangement.u It is a continuation ofthe common hepatic duct from the point of junction of that duct with the cystic duct. It courses centrally and inferiorly in the free margin of the lesser omental fold, passing behind the duodenum of the ampulla of Vater where it empties into the duodenum. Prinz, Howell, and Pickleman 15 list four anomalies of the extrahepatic ductal arrangements which may have clinical significance:

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(1) accessory bile ducts, (2) a right or left hepatic duct entering directly into the gallbladder, (3) a cystic duct that joins the right hepatic duct, and (4) a right hepatic duct that joins the cystic duct.

REFERENCES 1. Bengmark, S., and Rosengren, K.: Angiographic study of the collateral circulo'don to the liver atter ligation of the hepatic artery in man. Am. J. Surg., 119:620, 19/0. 2. Bilbey, D. L. J., and Rappaport, A. M.: Segmental anatomy of the human liver. Anat. Rec., 136:330,1960. 3. Dux. A., Biicheler, E., and Thurn, P.: Der arterielle Kollateralkreislaufder Leber. Fortsch. Rontgenstrahl, 105: 1, 1966. 4. Elias, H., and Petty, D.: Gross anatomy of the blood vessels and ducts within the human liver. Am. J. Anat., 90:59, 1952. 5. Goldsmith, N. A., and Woodburne, R. T.: The surgical anatomy pertaining to liver resection. Surg. Gynec. Obstet., 105:310, 1957. 6. Healey, J. E., Jr.: Clinical anatomic aspects of radical hepatic surgery. J. Int. CoIl. Surg., 22:542, 1954. 7. Healey, J. E., Jr., and Schroy, P. C.: Anatomy of the biliary ducts with the human liver: Analysis of the prevailing pattern of branchings and the major variations of the biliary ducts. Arch. Surg., 66:599, 1953. 8. Healey, J. E., Jr., Schroy, P., and Sorensen, R. J.: The intrahepatic distribution of the hepatic artery in man. J. Int. ColI. Surg., 20:133, 1953. 9. Hjortsjo, C. H.: Die Anatomie der intrahepatischen Gallengiinge beim Menschen, mittels Rontgen und Injektionstechnik studiert, nebst Beitriigen zur Kenntnis der inneren Lebertopographie. Kungl. Fysiogr., Sallskapets Handl., N. F., 59:1, 1948. 10. Jefferson, N. C., Hassan, M. J., Popper, H. J., and Necheles, H.: Formation of effective collateral circulation following excision of hepatic artery. Am. J. Physiol., 184 :589, 1956. 11. Lander. H. H., Lyman, R. Y., and Anson, B. J.: An anatomical consideration of the structures in the hepatic pedicle. A study of 100 consecutive cadavers. Quart. Bull. Northwest. Univ. Med. Sch., 15:103, 1941. 12. McDermott, W. V., Jr., et al.: Major hepatic resection: Diagnostic techniques and metabolic problems. Surgery, 54:51, 1963. 13. Mcindoe, A. H., and Counseller, V.: Bilaterality of the liver. Arch. Surg., 15 :589, 1927. 14. Michels, N. A.: Newer anatomy of liver-variant blood supply and collateral circulation. J.A.M.A., 172:125, 1960. 15. Prinz, R. A., Howell, H. S., and Pic kleman , J. R.: Surgical significance of extrahepatic biliary tree anomalies. Am. J. Surg., 131 :755, 1976. 16. Rex, H.: Beitrage zur Morphologie der Saugerleber. Morph. Jb., 14 :517, 1888. 17. Segall, H. N.: An experimental investigation of the blood and bile channels of the liver. Surg. Gynec. Obstet., 37:152, 1923. 18. Schiff, L.: Diseases of the Liver, 4th ed. Philadelphia, J. B. Lippincott Co., 1975. 19. Tiesenga, M. F., Neal, R. H., and Hemwall, G. A.: Jaundice in hepatic obstruction. J.A.M.A., 187:367, 1964. 530 El Camino Real Burlingame, California 94010