Principles of Surgery, Companion Handbook - page 30

ANATOMY

The liver constitutes approximately one-fiftieth of total body weight. True division into right and left lobes (hemilivers) is in line with the fossa for the inferior vena cava posteriorly and the gallbladder fossa anteroinferiorly (Cantlie's line). Couinaud proposed a functional division of the liver related to the hepatic venous drainage (Fig. 28-1).

FIGURE 28-1 The functional division of the liver and the segments according to Couinaud's nomenclature . (From: Bismuth H: Surgical anatomy and anatomical surgery of the liver. World J Surg 6:2, 1982, with permission.)

Biliary Drainage Each sector is drained by a major segmental duct. The anterior and posterior sectoral ducts in the right lobe join to form the right hepatic duct, whereas the medial and lateral segmental ducts in the left lobe terminate in the left hepatic duct, which joins the right duct to form a common hepatic duct in the porta hepatis.

Blood Supply The afferent blood supply to the liver arises from two sources: (1) the hepatic artery, which carries oxygenated blood and accounts for approximately 25 percent of hepatic blood flow, and (2) the portal vein, which accounts for approximately 75 percent of hepatic blood flow and drains the splanchnic circulation. The common hepatic artery originates from the celiac axis, and it bifurcates into a right and left branch to the left of the line dividing the right and left lobes. The major right hepatic artery originates from the superior mesenteric artery in 17 percent of people. Intrahepatic anastomoses between the right and left hepatic arteries do not occur. The cystic artery usually is an extrahepatic branch of the right hepatic artery.

The portal venous system returns to the liver the blood that the celiac, superior mesenteric, and inferior mesenteric arteries supply to the gastrointestinal (GI) tract , pancreas, and spleen. The vessel is formed behind the pancreas by the confluence of the superior mesenteric and splenic veins and, at times, the inferior mesenteric vein. The portal vein resides posteriorly in relation to the hepatic artery and bile duct in the hepatoduodenal ligament. In the porta hepatis, the vein divides into two branches, which course to each lobe. The hepatic venous system begins in the liver lobules as a central vein into which the sinusoids empty, forming collecting veins that gradually increase in size and coalesce to form the three major hepatic veins. Total hepatic blood flow is 1500 mL/min/1.73 m ² of body surface.

LIVER FUNCTION

The liver consists of four interrelated physiologic-anatomic units: the circulatory system, the biliary passages, the reticuloendothelial system, and functioning liver cells (hepatocytes).

Function Tests

The so-called liver function tests (Table 28-1) evaluate liver activity by assessing the degree of functional impairment .

TABLE 28-1 NORMAL VALUES FOR HEPATIC FUNCTION TESTS

Proteins Hepatic cells are responsible for the synthesis of albumin, fibrinogen, prothrombin, and other factors involved in blood clotting. Because the half-life of albumin is 21 days, impairment of hepatic synthesis must be present for over 3 weeks before abnormalities are noted.

Carbohydrates and Lipids Glycogenesis, glycogen storage, glycogenolysis, and the conversion of galactose into glucose all represent hepatic functions. Hypoglycemia is a rare accompaniment of extensive hepatic disease. The more common effect of hepatic disease is a deficiency of glycogenesis with resulting hyperglycemia. The liver is the major organ involved in the synthesis, esterification, and excretion of cholesterol. In the presence of parenchymal damage, both the total cholesterol and percentage of esterified fraction decrease.

Enzymes The three enzymes that achieve abnormal serum levels in hepatic disease and have been studied widely are alkaline phosphatase, serum glutamic oxalacetic transaminase (SGOT), and serum glutamic pyruvic transaminase (SGPT). SGOT is present in the liver, myocardium, skeletal muscles , kidney, and pancreas. Cellular damage in any of the above-mentioned tissues results in elevation of the serum level, and in the liver, most marked increases accompany acute cellular damage regardless of cause. Extremely high levels are noted in patients with hepatitis. SGPT is a more specific marker of liver disease. Elevations accompany acute hepatocellular damage. Serum alkaline phosphatase provides an indication of the patency of the bile channels. Elevation occurs in any form of obstruction including calculi, neoplasm, or intrahepatic cholestasis. In the presence of space-occupying lesions such as metastases, primary hepatic carcinoma, and abscesses, the alkaline phosphatase level also is increased. Nucleotidase levels are elevated in hepatobiliary disease.

Dye Excretion The hepatic removal of dyes from the circulation depends on hepatic blood flow, hepatocellular function, and biliary excretion. The presence of jaundice, fever , shock , hemorrhage, or cellular damage causes a disproportionate indocyanine green or sulfobromophthalein (Bromsulphalein) retention.

Coagulation Factors In liver disease, multiple coagulation defects may occur. Two mechanisms contribute to the deficiency of coagulation factors: (1) in obstructive jaundice, the bile source required for the absorption of the fat-soluble vitamin K results in a decreased synthesis of prothrombin, and (2) hepatocellular dysfunction is accompanied by an inability of the liver to synthesize prothrombin. Decreases in factors V, VII, and IX and fibrinogen also have been noted in hepatic disease. Cirrhosis may have increased fibrinolysis.

SPECIAL STUDIES

Needle Biopsy Almost 100 percent accuracy has been demonstrated for both posthepatitic and postnecrotic cirrhosis. Intrahepatic cholestasis, hepatitis, and cellular degeneration resulting from toxicity are readily diagnosed. Focal lesions occassionally may be missed. Needle biopsy is contraindicated for suspected hemangioma.

Ultrasound , Computed Tomography , Magnetic Resonance Imaging, and Scintigrams Preoperative ultrasound (US) has its highest yield in defining hepatic abscesses, cystic lesions, and most hemangiomas . US and duplex scanning can determine the patency of a portasystemic shunt noninvasively. Computed tomography (CT) is used with or without vascular enhancement. For most lesions, CT provides the best results. Magnetic resonance imaging (MRI) is particularly applicable for assessing vascular lesions.

Angiography Angiography may depict hepatic tumors, both primary and metastatic. When used in conjunction with CT, sensitivity and specificity are increased. Angiography also demonstrates extrahepatic vascular anatomy and provides a road map for the surgeon.

TRAUMA

See Chap. 6, Trauma.

HEPATIC ABSCESSES

Hepatic abscesses are related to two distinct groups of pathogens: pyogenic bacteria and Entamoeba histolytica.

Pyogenic Abscesses

Incidence The highest percentage occur in the sixth and seventh decades.

Etiology Causes include (1) ascending biliary infection, (2) hematogenous spread via the portal venous system, (3) generalized septicemia with involvement of the liver by way of the hepatic arterial circulation, (4) direct extension from intraperitoneal infection, or (5) other causes, including hepatic trauma. The most frequent antecedent cause has been cholangitis secondary to calculi or carcinoma in the extrahepatic biliary duct system. The second most common cause is related to generalized septicemia. There is an increased incidence in immunocompromised patients. Cultures are positive in over 90 percent; Escherichia coli, Klebsiella, and Streptococcus are most commonly isolated. Staphylococcus and Pseudomonas are occurring more frequently, and mixed bacterial and fungal abscesses are noted in about 25 percent. Abscesses may be solitary, multiple, and multilocular.

Clinical Manifestations The primary clinical manifestation is fever, frequently accompanied by chills, profuse sweating, nausea, vomiting, and anorexia . Pain is a late symptom and is more common with large, solitary abscesses. Hepatic tenderness is present in 50 percent.

Diagnostic Studies Leukocytosis is usual; anemia is frequent. Positive blood cultures are seen in 40 percent of patients. Liver function tests are not diagnostic, but elevation of the alkaline phosphatase level is the most frequent abnormality. CT scan is the most accurate radiographic study (over 90 percent), followed by US (80 percent) and radionuclide scans (70 percent).

Treatment Treatment is based on appropriate antibiotic therapy combined with drainage in selected patients. Intravenous antibiotics are usually administered for 2 weeks, followed by 1 month of oral therapy . Abscesses may be drained percutaneously under US or CT control. Equivalent results have been reported for percutaneous and surgical drainage. Surgical access may be transthoracic or transabdominal. Occasionally, for multiple abscesses confined to a lobe, treatment is best managed by resection.

Prognosis and Complications For percutaneous and surgical drainage, there is 7.5–20 percent mortality (for multiple abscesses, the rate is significantly increased).

Amebic Abscesses

Ten percent of the population is infected with Entamoeba histolytica. Amebic abscesses usually are diagnosed in middle-aged adults with male- female ratio of 9:1. Organisms reach the liver via the portal system. The abscess is usually a solitary right lobe abscess with anchovy paste fluid.

Clinical Manifestations Clinical manifestations include fever, liver pain (88 percent), and occasionally right shoulder pain. Fever with diaphoresis and rigors is seen in 75 percent. Fifty percent of patients show antecedent diarrhea; bloody, mucous stools are seen in children. The liver is tender and enlarged on examination. Jaundice is rare.

Diagnostic Studies/Complications Leukocytosis and anemia accompany prolonged disease. The recovery rate of ameba in stool is 15.4 percent. Liver function tests are not helpful. The indirect hemagglutination test usually is positive. Scans also are useful. Aspiration of the cavity shows characteristic material, trophozoites in less than one-third. Secondary bacterial infection is evident in 22 percent. Abscesses may rupture (6–9 percent) or extend into adjacent organs.

Treatment Amebicidal drugs are used first; metronidazole is the drug of choice. Treatment may require aspiration and drainage if symptoms persist, the abscess remains apparent radiographically, or it is secondarily infected.

Prognosis The mortality rate is less than 5 percent in uncomplicated cases; with complications, the rate can rise to 43 percent.

CYSTS AND BENIGN TUMORS

Nonparasitic Cysts

These include degenerative, dermoid, lymphatic, retention, and proliferative cysts. Solitary cysts usually occur in the right lobe and have clear contents. The liver may be honeycombed, polycystic, which is associated with polycystic kidneys. Rarely, a polycystic liver may cause portal hypertension. Traumatic cysts usually are single and filled with bile. Cystadenomas are filled with mucoid material. Cysts usually grow slowly with few symptoms and present as painless right upper quadrant masses. Symptoms result from pressure on adjacent organs. Pain occurs with rupture, torsion, or hemorrhage. Jaundice is rare. Liver function tests have little value. CT and US are very useful for diagnosis.

Treatment Asymptomatic cysts require observation only. Surgical treatment can consist of complete extirpation. Large, deep, sterile cysts may be widely unroofed. Purulent contents demand external drainage. Polycystic livers may require nonanatomic resection and wide fenestration. Prognosis follows that of the associated renal polycystic disease, if any.

Hydatid Cysts

Hydatid cysts usually are unilocular and caused by Echinococcus granulosus. The alveolar type is caused by E. multiocularis. Seventy percent are located in the liver; one-third are multiple. The right lobe is affected in 85 percent. The cyst is two-layered and encapsulated with the contents under pressure and is colorless, opalescent. Daughter cysts can be inside the main cyst. Alveolar disease has no capsule with multiple metastases, blood, and lymphatic invasion.

Complications Complications include intrabiliary rupture (5–10 percent), suppuration with biliary bacteria, and intraperitoneal or intrapleural rupture.

Clinical Manifestations These cysts usually are asymptomatic. Early symptoms result from pressure on adjacent organs. Pain, tenderness, and palpable mass are common. If the cyst is secondarily infected, symptoms are those of pyogenic abscess. Hydatid cyst may present with anaphylaxis if there is an intraperitoneal rupture. Biliary rupture can present with colic, jaundice, and urticaria.

Diagnostic Studies Round, calcified shadows are seen on plain films . CT scan is very useful. Indirect agglutination is positive in 85 percent. Casoni's skin test is positive in 90 percent.

Treatment Treatment is surgical. Cysts must be removed without contaminating the peritoneal cavity. Cysts may be drained intraoperatively and flushed with hypertonic saline, alcohol, or hibitane before excision . Large cysts may require partial hepatectomy. The cavity may be managed by omentoplasty and simple closure. External drainage has a high complication rate. In the past, alveolar disease of the liver was inevitably fatal, but more recently, satisfactory results have been obtained with extensive hepatic resection.

Benign Tumors

Hamartoma This lesion is composed of normal tissues arranged in disorderly fashion. Hamartomas are firm, nodular, encapsulated, and cystic and usually are of no clinical significance.

Adenoma This tumor may be related to oral contraceptives, pregnancy , diabetes mellitus, or glycogen storage disease. It should be resected particularly if it is enlarging or bleeding. Because of the risk of bleeding and malignant potential, adenomas should be removed.

Focal Nodular Hyperplasia (FNH) Focal nodular hyperplasia is a solitary, tan, unencapsulated tumor near the liver edge that usually is asymptomatic; it rarely ruptures. It should be resected only if symptomatic. Deep biopsy is necessary for diagnosis.

Hemangioma This is the most common liver nodule. The female-male ratio is 5:1. There is no malignant potential. Most hemangiomas are asymptomatic; bruit is rare. Symptoms are related to size. They rarely rupture and hemorrhage. Diagnosis is by angiography, CT, US, MRI, or scintigram. Avoid needle biopsy because of bleeding. Infants may have high-output congestive heart failure and may respond to steroids or hepatic artery ligation. Adults should only be resected for symptoms and when size is greater than 4–5 cm.

MALIGNANT TUMORS

Primary Carcinoma

Incidence Primary liver carcinoma is common in Asians and African aborigines. In children, hepatoblastoma is common before age 2. Aflatoxins and low-protein diets have been implicated etiologically. Postnecrotic cirrhosis frequently precedes, with serologic markers for hepatitis B virus or hepatitis C antibody in patients living in endemic areas.

Pathology Hepatocellular carcinoma (most common), followed by cholangiocarcinoma (bile duct cancer) and hepatoblastoma, an immature variant in children. Fibrolamellar carcinoma is a hepatocellular variant occurring in young adults.

There is frequent invasion of the portal and hepatic veins. Extension is via (1) centrifugal growth, (2) parasinusoidal extension, (3) venous spread, and (4) distal metastasis by lymphatic and vascular systems, most often to nodes and lungs. Metastases occurs in 48–73 percent.

Clinical Manifestations Weight loss and fatigue are evident in 80 percent, pain in 50 percent. Hepatomegaly is very common; splenomegaly and portal hypertension are likely in 33 percent. Jaundice and ascites are common. Children usually present with a mass.

Diagnostic Evaluation Alkaline phosphatase and 5'-nucleotidase levels usually are elevated. The bilirubin level often is normal. Alpha-fetoprotein (AFP) is present in 30–75 percent. Arteriography and CT/MRI are useful. Preoperative needle biopsy also is useful. Intraoperative US is used to define resection limits.

Treatment The only chance for survival is surgical excision. Cirrhosis compromises resection possibilities. Use of intraoperative US has permitted limited resections, particularly in cirrhotic patients. Transarterial chemoembolization has achieved 1-, 2-, and 5-year survival rates of 51, 24, and 6 percent, respectively, while decreasing the tumor size in almost 33 percent of patients. Unresectable hepatocellular carcinomas may be converted to resectable lesions with combined radiation and chemotherapy.

Percutaneous ethanol injection has resulted in the disappearance of tumors less than 4.5 cm in diameter. Cryosurgery using an intraoperatively placed probe that delivers liquid nitrogen also has effected tumor necrosis and destruction. Transplantation and resection yield equivalent 5-year survival rates of approximately 50 percent, but the recurrence rate is lower in patients who were transplanted. Transplantation achieves the best results in patients with small, uninodular or binodular lesions. Resection of extrahepatic recurrences of hepatocellular carcinomas has resulted in several 5-year survivals.

In the case of hepatoblastoma, particularly in children, lesions often deemed not resectable can be converted into resectable tumors that have potential for cure. A combination of preoperative chemotherapy followed by resection has resulted in a cure rate of 90 percent in children.

Prognosis Prognosis is extremely poor for adults but better for fibrolamellar carcinoma. Resectable children under age 2 have better survivals.

OTHER PRIMARY NEOPLASMS

These include angiosarcomas (vinyl chloride, Thorotrast), mesenchymomas, and infantile hemangioendotheliomas.

Metastatic Neoplasms

Metastatic neoplasms are the most common malignant liver tumor with a ratio 20:1 to primary tumors. Metastases in the liver are noted in 25–50 percent of all cancer deaths. Routes to the liver are via (1) portal vein, (2) lymphatics, (3) hepatic artery, and (4) direct extension. Metastases often grow more rapidly than the original lesion.

Clinical Manifestations Symptoms are evident in 67 percent, with pain, ascites, jaundice, anorexia, and weight loss. A mass is seen in 50 percent. Flushing is evident in hepatic carcinoid.

Diagnosis The alkaline phosphatase level is elevated in over 80 percent, SGOT elevation is seen in 67 percent, and the AFT level is normal. Carcinoembryonic antigen (CEA) may be elevated in colon metastases. CT/MRI, particularly CT with intraarterial infusion, angiography, and intraoperative US are all useful.

Treatment Resection should be considered if (1) the primary is controlled, (2) there are no other metastases, (3) the patient will tolerate the procedure, and (4) total extirpation is possible. Resection of metastases has a survival benefit for colorectal carcinoma and Wilms' tumor. Twenty percent of colon carcinomas have metastases, of which 25 percent are resectable; 50 percent have other negating factors. A multi-institutional study of liver resection for colorectal metastases reported a 33 percent 5-year survival and a 21 percent 5-year disease-free survival. Colorectal hepatic metastases, initially considered unresectable, have been treated with doxorubicin. This resulted in regression to a size that permited resection.

Intraarterial infusion chemotherapy may provide symptomatic relief, but most series show no improvement over intravenous therapy. Cures of metastatic Wilms' tumor by liver resection combined with chemotherapy and radiation have been reported.

HEPATIC RESECTION

Indications include (1) trauma with devascularization of hepatic tissue, (2) cysts, (3) granulomas, (4) primary neoplasms, and (5) secondary neoplasms. Up to 80 percent resection may be tolerated in noncirrhotics. Regeneration occurs from marked hypertrophy of remaining tissue . Insulin is an anabolic factor.

Management of the Patient Preoperative therapy is directed at maintaining optimal liver function and correcting any defects that may be present. A diet high in calories , proteins, and carbohydrates is used, and the administration of albumin may be required to achieve normal levels. Vitamin K is given routinely until a normal prothrombin time results. In the presence of jaundice, other fat-soluble vitamins are added. Fresh frozen plasma will rapidly replenish coagulation factors. Because many patients have a reduced hematocrit, transfusion with fresh whole blood rich in platelets and coagulation factors is indicated. Major hepatic resection is attended by a prohibitive mortality rate in the patient with sulfobromophthalein retention greater than 35 percent, a serum albumin level lower than 2.0 g, and an increased prothrombin time that does not respond to parenteral vitamin K. Postoperatively, infusion of 10% glucose is continued until the patient maintains an adequate oral intake to obviate severe hypoglycemia, which has been reported. After more intensive resections, daily administration of 25–50 g albumin usually is required for 7–10 days to maintain the serum level above 3 g/dL. Antibiotics are administered prophylactically. Analgesics and hypnotics that are detoxified by the liver are used only sparingly. Intraabdominal abscess formation and sepsis are the most common complications of major hepatic resection, occurring in 20–30 percent of patients. Subphrenic abscesses usually can be managed with percutaneous drainage.

Operative Procedures The major aim is to prevent/control hemorrhage. The porta hepatis may be clamped safely for 60 min. Resection follows anatomic planes of segmental anatomy based on portal distribution. The liver is mobilized by dividing the triangular ligament, coronary ligament, and ligamentum teres. Porta hepatis dissection defines the artery, vein, and duct to be removed, which are temporarily occluded. Glisson's capsule is incised, and the hepatic parenchyma is cleaved bluntly, ligating ducts and vessels and heading toward the hepatic veins, which are then doubly ligated at the cava. This is followed by division of porta hepatis structures.

On the basis of new concepts of segmental anatomy, the following classification of hepatic resection is applicable (Fig. 28-2): (1) Subsegmental or wedge resection is removal of an area of the liver that is less than a segment and without an anatomic dissection plane. (2) Left lateral segmentectomy (formerly left lobectomy) is excision of the liver mass to the left of the left segmental fissure along an anatomic plane. (3) Left medial segmentectomy is resection between the main interlobar fissure and the left segmental fissure. (4) Left lobectomy (left hepatectomy) is excision of all hepatic tissue to the left of the main lobar fissure. (5) Right lobectomy (right hepatectomy) is removal of the liver to the right of the main lobar fissure. (6) Extended right lobectomy is excision of the entire lobe plus the medial segment of the left lobe (trisegmentectomy), i.e., excision of all tissue to the right of the umbilical fossa, fossa for the ligamentum venosum, and the ligamentum teres. Based on portal distribution, there are eight hepatic segments that can be resected individually or as combinations (see Fig. 28-1).

FIGURE 28-2 Nomenclature for hepatic resection.

PORTAL HYPERTENSION

Etiology (Table 28-2) The causes include (1) increased inflow (rare), (2) extrahepatic outflow obstruction, (3) extrahepatic portal obstruction, and (4) intrahepatic obstruction. The overwhelming majority (>90 percent) of cases result from intrahepatic obstruction. Contributing factors include (1) fibrosis with portal venule compression, (2) compression by regenerative nodules, (3) increased arterial flow, (4) fatty infiltration and inflammation , and (5) intrahepatic vascular obstruction. Nutritional cirrhosis is the most common cause worldwide, which is related to ethanol consumption in Western civilization. Resistance to flow is postsinusoidal (on the hepatic venous side of the sinusoid). Postnecrotic cirrhosis accounts for up to 12 percent but represents the major cause in the Orient.