The liver and biliary tract

14 The liver and biliary tract





The liver



Anatomy


The liver is the largest abdominal organ, weighing approximately 1500 g. It extends from the fifth intercostal space to the right costal margin. It is triangular in shape, its apex reaching the left midclavicular line in the fifth intercostal space. In the recumbent position, the liver is impalpable under cover of the ribs. The liver is attached to the undersurface of the diaphragm by suspensory ligaments that enclose a ‘bare area’, the only part of its surface without a peritoneal covering. Its inferior or visceral surface lies on the right kidney, duodenum, colon and stomach.


Topographically, the liver is divided by the attachment of the falciform ligament into right and left lobes; fissures on its visceral surface demarcate two further lobes, the quadrate and caudate (Fig. 14.1A). However, it is the liver segmental anatomy, as defined by the distribution of its blood supply, that is important to the surgeon.





Blood supply and function


The liver normally receives 1500 ml of blood per minute and has a dual blood supply, 75% coming from the portal vein and 25% from the hepatic artery, which supplies 50% of the oxygen requirements. The principal venous drainage of the liver is by the right, middle and left hepatic veins, which enter the vena cava (Fig. 14.1B). In 25% of individuals, there is an inferior right hepatic vein, and numerous small veins drain direct into the vena cava from the caudate lobe (segment I). The functional unit of the liver is the hepatic acinus. Sheets of liver cells (hepatocytes) one cell thick are separated by interlacing sinusoids through which blood flows from the peripheral portal tract into the hepatic acinus to the central branch of the hepatic venous system. Bile is secreted by the liver cells and passes in the opposite direction along the small canaliculi into interlobular bile ducts located in the portal tracts (Fig. 14.2).



The liver has an important role in nutrient metabolism and is responsible for storing glucose in the form of glycogen, or converting it to lactate for release into the systemic circulation. Amino acids are utilized for hepatic and plasma protein synthesis or catabolized to urea. The liver has a central role in the metabolism of lipids, bilirubin and bile salts, drugs and alcohol. It is the principal organ for storage of a number of minerals and vitamins, and is responsible for the production of the coagulation factors I, V, XI, the vitamin K-dependent factors II, VII, IX and X as well as proteins C and S and antithrombin. The liver is also the largest reticuloendothelial organ in the body and its Kupffer cells play a role in the removal of damaged red blood cells, bacteria, viruses and endotoxin, much of which enter the body from the gut.




Jaundice


Jaundice is caused by an increase in the level of circulating bilirubin and becomes obvious in the skin and sclera when levels exceed 50 μmol/l (Fig. 14.3). It may result from excessive destruction of red cells (haemolytic jaundice), from failure to remove bilirubin from the blood stream (hepatocellular jaundice), or from obstruction to the flow of bile from the liver (cholestatic jaundice) (Fig. 14.4). Congenital non-haemolytic hyperbilirubinaemia (Gilbert’s syndrome) is a relatively rare cause of jaundice due to defective bilirubin transport; the jaundice is usually mild and transient, and the prognosis is excellent.




To the surgeon, the most important type of haemolytic jaundice is that caused by hereditary spherocytosis, in which splenectomy may be necessary (Ch. 15). Haemolytic jaundice may also occur after blood transfusion and after operative or accidental trauma, when haematoma formation produces a pigment load that exceeds hepatic excretory capacity.


Hepatocellular jaundice is usually a medical rather than a surgical condition, although its recognition in patients presenting with abdominal pain is important, as surgical intervention may aggravate the hepatocellular injury.


Cholestatic jaundice due to intrahepatic obstruction of bile canaliculi may be a feature of acute and chronic liver disease and can be caused by drugs (e.g. chlorpromazine). This form of jaundice must be differentiated from that due to extra-hepatic obstruction, the cause of which has most surgical relevance. Extrahepatic obstruction most commonly results from gallstones or cancer of the head of the pancreas. Other causes include cancer of the periampullary region or major bile ducts, extrinsic compression of the bile ducts by metastatic tumour, iatrogenic biliary stricture and choledochal cyst.



Diagnosis



History and clinical examination


An accurate, rapid diagnosis of the cause of jaundice allows prompt institution of appropriate treatment (Fig. 14.5). The age, sex, occupation, social habits, drug and alcohol intake, history of injections or infusions, and general demeanour of the patient must be considered. A history of intermittent pain, fluctuant jaundice and dyspepsia suggests calculous obstruction of the common bile duct, whereas a history of weight loss and relentless progressive jaundice favours a diagnosis of neoplasia. Obstructive jaundice is likely if there is a history of passage of dark urine and pale stools, and if the patient complains of pruritus (owing to an inability to secrete bile salts into the obstructed biliary system). Hepatocellular jaundice is likely if there are stigmata of chronic liver disease, such as liver palms, spider naevi, testicular atrophy and gynaecomastia. The abdomen must be examined for evidence of hepatomegaly or gallbladder distension, and for signs of portal hypertension such as splenomegaly, ascites and large collateral veins (caput medusae) in the abdominal wall.




Biochemical and haematological investigations


Haemolytic jaundice is suggested if there are high circulating levels of unconjugated bilirubin but no bilirubin in the urine. Serum concentrations of liver enzymes are normal in these circumstances and the appropriate haematological investigations should be set in train.


In jaundice due to biliary obstruction, the circulating bilirubin is conjugated by the liver and rendered water-soluble; it can then be excreted in the urine and gives it a dark colour. As bile cannot pass into the gastrointestinal tract, the stool becomes pale and urobilinogen is absent from the urine. Obstruction increases the formation of alkaline phosphatase from the cells lining the biliary canaliculi, producing raised serum levels. This rise precedes that of bilirubin and its fall is more gradual once obstruction is relieved. Serum transaminase and lactic dehydrogenase levels may rise in obstruction. Conversely, swelling of the parenchyma in hepatocellular jaundice frequently produces an element of intrahepatic biliary obstruction and a modest rise in serum alkaline phosphatase concentration.


Full blood count and coagulation screen should be undertaken as a matter of routine and viral status should be determined. Anaemia may signify occult blood loss, and a low white cell or platelet count may indicate hypersplenism due to portal hypertension. Prolongation of the prothrombin time may be present in both hepatocellular and cholestatic jaundice, but should readily correct within 36 hours with the administration of parenteral vitamin K when jaundice is cholestatic.



Radiological investigations


If the clinical picture and biochemical investigations suggest that jaundice is obstructive, radiological techniques can be used to define the site and nature of the obstruction.












Congenital abnormalities


Up to 5% of the population has simple liver cysts. They are lined by biliary epithelium and contain serous fluid, but never communicate with the biliary tree. They rarely produce symptoms, are associated with normal liver function, and on ultrasound or CT have no discernible wall (Fig. 14.6). In the few patients who develop symptoms, cysts tend to recur following aspiration, and sclerosis by alcohol injection is of little value for large symptomatic cysts. Surgical management consists of deroofing and may be undertaken by laparoscopic means. Polycystic disease is a rare cause of liver enlargement and may be associated with polycystic kidneys as an autosomal dominant trait. In symptomatic patients, it may be necessary to combine a deroofing procedure with hepatic resection or to consider liver transplantation.




Cavernous haemangiomas are one of the most common benign tumours of the liver (up to 5% of population) and may be congenital. Women are affected six times more frequently than men. Most haemangiomas are small solitary subcapsular growths found incidentally at laparotomy or autopsy, but they are sometimes detected on ultrasound examination as densely hyperechoic lesions that mimic hepatic tumours. These lesions rarely give rise to pain. Resection may be considered for symptomatic lesions exceeding 5 cm in diameter.




Hepatic infections and infestations


Liver abscesses can be classified as bacterial, parasitic or fungal. Bacterial abscess is the most common type in Western medicine, but parasitic infestation is an important cause world-wide. Fungal abscesses are found in patients receiving long-term broad-spectrum antibiotic treatment or immunosuppressive therapy, and may complicate actinomycosis.



Pyogenic liver abscess


Infection from the biliary system is now more common due to the increasing use of radiological and endoscopic intervention. Infection may spread through the portal vein from abdominal sepsis (e.g. appendicitis, diverticulitis), via the hepatic artery from a septic focus anywhere in the body, or by direct spread from a contiguous organ (e.g. empyema of the gallbladder). Abscess formation may follow blunt or penetrating injury, and in one-third of patients the source of infection is indeterminate (cryptogenic). Common organisms are:








Hydatid disease


This less common infestation is caused in humans by one of two forms of tapeworm, Echinococcus granulosus and E. multilocularis. The adult tapeworm lives in the intestine of the dog, from which ova are passed in the stool; sheep or goats serve as the intermediate host by ingesting the ova whereas humans are accidental hosts (Fig. 14.7). The condition is most common in sheep- and goat-rearing areas. Ingested ova hatch in the duodenum and the embryos pass to the liver through the portal venous system. The wall of the resulting hydatid cyst is surrounded by an adventitial layer of fibrous tissue and consists of a laminated membrane lined by germinal epithelium, on which brood capsules containing scolices develop.







Portal hypertension


Portal hypertension is caused by increased resistance to portal venous blood flow, the obstruction being prehepatic, hepatic or posthepatic (Table 14.1). Rarely, it results primarily from an increase in portal blood flow. The normal pressure of 5–15 cmH2O in the portal vein is consistently exceeded (above 25 cmH2O). Portal vein thrombosis is a rare cause and is most commonly due to neonatal umbilical sepsis. The most common cause of portal hypertension is cirrhosis resulting from chronic liver disease and is characterized by liver cell damage, fibrosis and nodular regeneration. The fibrosis obstructs portal venous return and portal hypertension develops. Arteriovenous shunts within the liver also contribute to the hypertension.


Table 14.1 Causes of portal hypertension





















Obstruction to portal flow:
Prehepatic

Intrahepatic

Posthepatic

Increased blood flow (rare)


Alcohol is the most common aetiological factor in developed countries, whereas in North Africa, the Middle East and China, schistosomiasis due to Schistosoma mansonii is a common cause. Chronic active hepatitis and primary and secondary biliary cirrhosis may result in portal hypertension, but in a large number of patients the cause remains obscure (cryptogenic cirrhosis).


Post-hepatic portal hypertension is rare. It is most frequently due to spontaneous thrombosis of the hepatic veins and this has been associated with neoplasia, oral contraceptive agents, polycythaemia and the presence of abnormal coagulants in the blood. The resulting Budd-Chiari syndrome is characterized by portal hypertension, caudate hypertrophy, liver failure and gross ascites.



Effects of portal hypertension


As a result of gradual chronic occlusion of the portal venous system, collateral pathways develop between the portal and systemic venous circulations. Portosystemic shunting occurs at three principal sites (Fig. 14.8). The most important is the development of varices in the submucosal plexus of veins in the lower oesophagus and gastric fundus. Oesophageal varices may rupture, to cause acute massive gastrointestinal bleeding in about 40% of patients with cirrhosis. The initial episode of variceal haemorrhage is fatal in about one-third of patients, and recurrent haemorrhage is common. Bleeding from retroperitoneal and periumbilical collaterals (‘caput medusae’) is troublesome during abdominal surgery, and collaterals may develop and cause bleeding at the site of stomas. Anorectal varices are not uncommonly found at proctoscopy but rarely cause bleeding.



Progressive enlargement of the spleen occurs as a result of vascular engorgement and associated hypertrophy. Haematological consequences are anaemia, thrombocytopenia and leucopenia (with the resulting syndrome of hypersplenism). Ascites may develop and is due to increased formation of hepatic and splanchnic lymph, hypoalbuminaemia, and retention of salt and water. Increased aldosterone and antidiuretic hormone levels may contribute. Portosystemic encephalopathy is due to an increased level of toxins such as ammonia in the systemic circulation. This is particularly likely to develop where there are large spontaneous or surgically created portosystemic shunts. Gastrointestinal haemorrhage increases the absorption of nitrogenous products and may precipitate encephalopathy.




Acute variceal bleeding


Patients presenting with acute upper gastrointestinal bleeding are examined for evidence of chronic liver disease (EBM 14.1). The key investigation during an episode of active bleeding is endoscopy. This allows the detection of varices and defines whether they are or have been the site of bleeding. It is important to remember that peptic ulcer and gastritis are common complaints that occur in 20% of patients with varices.




Management


The priorities in the management of bleeding oesophageal varices are summarized in Table 14.3.


Table 14.3 Priorities in the management of bleeding oesophageal varices

























Active resuscitation

Assessment of coagulation status

Urgent endoscopy
Control of bleeding

Treatment of hepatocellular decompensation
Treatment/prevention of portosystemic encephalopathy
Prevention of further bleeding from varices




Endoscopy and control of bleeding

Endoscopy will reveal tortuous varices in three columns most prominent in the lower third of the oesophagus. Haemorrhage usually occurs from varices at the lowest few centimetres of the oesophagus. Rarely, bleeding occurs from varices in the gastric fundus. Although the synthetic form of somatostatin, octreotide, can be used to lower portal venous pressure and arrest bleeding, the injection of a sclerosant such as ethanolamine, or the application of bands is now used to arrest the bleeding at endoscopy (EBM 14.2). If haemorrhage is torrential and prevents direct injection, balloon tamponade may be used to stop the bleeding. The four-lumen Minnesota tube (Fig. 14.9) has largely replaced the three-lumen Sengstaken–Blakemore tube. The four lumina allow:



Mar 20, 2017 | Posted by in GENERAL SURGERY | Comments Off on The liver and biliary tract

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