Obstruction of the biliary tract

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•132• Chapter 12 Obstruction of the Biliary Tract R. Darko Introduction The obstruction of the biliary tree may be intrahepatic or extrahepatic. It may also be partial or complete. When obstruction is significant the classical symptoms of jaundice, pruritus, pale stools and dark urine are prominent. Most cases of intra hepatic bile duct obstruction are not amenable for surgical repair and therefore emphasis will be placed on extrahepatic bile duct obstruction. PREVALENCE OF THE DISEASE: The true incidence of the disease in Ghana is unknown but it is generally believed that carcinoma of the head of pancreas is the commonest cause, followed by a gall stone causing the biliary obstruction. The only paper published in West Africa was by Rahman et al. (2011) in which he described 64 cases seen over a 5-year period and found carcinoma of the head of pancreas constituting 60 percent of cases.1 There are many ways of classifying bile duct obstruction. The vast majority of bile duct obstructions are due to tumours or gall stones but the one classification that allows easy clinical identification is one that puts the cases into one of these four categories based on the behaviour of the jaundice. 1. Progressive jaundice: here it is common to find that the obstruction is complete and the jaundice becomes increasingly severe. They are all caused by tumour of the biliary tree except periampulary tumours. Included in this list is inadvertent ligation of the common bile duct and an impacted gallstone at the lower end of the bile duct. 2. Fluctuating jaundice: here the bile duct gets blocked and for a reason becomes unblocked again. The cycle then repeats itself. This is the typical behaviour of a stone in the common •133• Obstruction of the Biliary Tract bile duct which is not impacted. When the stone is impacted it gives rise to progressive jaundice. Other causes include periampullary tumours, intrabiliary parasites, choledochal cysts, duodenal diverticuli and papilloma of the bile duct. 3. Chronic continuous obstruction: In this situation there is gradual stricture of the duct and usually does not proceed to rapid complete obstruction. This is seen in benign strictures of the bile duct. Other causes include chronic pancreatitis and stenosis of bilio-enteric anastomosis. 4. Segmental obstruction: If only a few segmental ducts are obstructed since the liver has a large reserve, jaundice may not appear but the alkaline phosphatase will rise. The causes include tumours, injury and stones that involve only a few segments of the biliary tree in the liver.2 Pathophysiology of Bile Duct Obstruction In the patient with bile duct obstruction there is hepatic dysfunction as well as systemic effects. With bile duct obstruction, the intrahepatic canaliculi become dilated and tortuous. The pressure in the bile duct is normally low (5-10cm of water) When bile duct pressure increases to more than 300mm of water, hepatic bile duct secretion ceases.3 As a result the excretory products of the hepatocytes reflux directly into the vascular system resulting in systemic toxicity. In the jaundiced patient, there is decreased capacity to excrete drugs that are normally secreted into bile.4 High levels of bile acids induce apaptosis.5 The synthesis of substances like albumin, clotting factors and immunoglobulins is considerably reduced. The Kupffer cell function, including phagocytosis, clearance of bacteria and endotoxins is considerably reduced. Decreased cardiac function and reduced total peripheral resistance may make the jaundiced patient more susceptible to the development of post-operative shock than non-jaundiced patients. Decreased cardiac function, hypovolaemia and endotoxaemia may be the leading factors in the development of renal failure in the jaundiced patient. •134• Chapter 12 The increased levels of bile acids may be the cause of increased diuresis that occurs in biliary obstruction.6 Coagulation is impaired due to the reduced vitamin K absorption resulting from the lack of bile salts to aid the absorption of fat soluble vitamins. Surgery in the jaundiced patient also results in reduced immunity leading to increased post-operative septic conditions. There is an increased incidence of wound failure with increased incidence of incisional hernia in patients who undergo operation for obstructive jaundice. In bile duct obstruction usually there is dilatation of the portion proximal to area of obstruction. The degree of dilatation depends on the tissue that supports the intrahepatic bile ducts and how pliable the extra hepatic bile ducts are. Physiology of Bile Under normal circumstances 0.5-1.5 litres of bile is secreted each day into...