Excerpt from Biliary Obstruction

Please click here to view the full topic text: Biliary Obstruction

Background

Disorders of the biliary tract affect a significant portion of the worldwide population, and the overwhelming majority of cases are attributable to cholelithiasis (gallstones). In the United States, 20% of persons older than 65 years have gallstones and 1 million newly diagnosed cases of gallstones are reported each year.

To better understand these disorders, a brief discussion of the normal structure and function of the biliary tree is needed. Bile is the exocrine secretion of the liver and is produced continuously by hepatocytes. It contains cholesterol and waste products, such as bilirubin and bile salts, which aid in the digestion of fats. Half the bile produced runs directly from the liver into the duodenum via a system of ducts, ultimately draining into the common bile duct (CBD). The remaining 50% is stored in the gallbladder. In response to a meal, this bile is released from the gallbladder via the cystic duct, which joins the hepatic ducts from the liver to form the CBD. The CBD courses through the head of the pancreas for approximately 2 cm before passing through the ampulla of Vater into the duodenum.

Pathophysiology

Biliary obstruction refers to the blockage of any duct that carries bile from the liver to the gallbladder or from the gallbladder to the small intestine. This can occur at various levels within the biliary system. The major signs and symptoms of biliary obstruction result directly from the failure of bile to reach its proper destination.

The clinical setting of cholestasis or failure of biliary flow may be due to biliary obstruction by mechanical means or by metabolic factors in the hepatic cells. For the sake of simplicity, the primary focus of this article is mechanical causes of biliary obstruction, further separating them into intrahepatic and extrahepatic causes. The discussion of intracellular/metabolic causes of cholestasis is very complex, the pathogenesis of which is not always clearly defined. Therefore, these causes are mentioned but are not discussed in detail.

Intrahepatic cholestasis generally occurs at the level of the hepatocyte or biliary canalicular membrane. Causes include hepatocellular disease (eg, viral hepatitis, drug-induced hepatitis), drug-induced cholestasis, biliary cirrhosis, and alcoholic liver disease. In hepatocellular disease, interference in the 3 major steps of bilirubin metabolism, ie, uptake, conjugation, and excretion, usually occurs. Excretion is the rate-limiting step and is usually impaired to the greatest extent. As a result, conjugated bilirubin predominates in the serum.

Extrahepatic obstruction to the flow of bile may occur within the ducts or secondary to external compression. Overall, gallstones are the most common cause of biliary obstruction. Other causes of blockage within the ducts include malignancy, infection, and biliary cirrhosis. External compression of the ducts may occur secondary to inflammation (eg, pancreatitis) and malignancy. Regardless of the cause, the physical obstruction causes a predominantly conjugated hyperbilirubinemia.

Accumulation of bilirubin in the bloodstream and subsequent deposition in the skin causes jaundice (icterus). Conjunctival icterus is generally a more sensitive sign of hyperbilirubinemia than generalized jaundice. Total serum bilirubin values are normally 0.2-1.2 mg/dL. Jaundice may not be clinically recognizable until levels are at least 3 mg/dL. Urine bilirubin is normally absent. When it is present, only conjugated bilirubin is passed into the urine. This may be evidenced by dark-colored urine seen in patients with obstructive jaundice or jaundice due to hepatocellular injury. However, reagent strips are very sensitive to bilirubin, detecting as little as 0.05 mg/dL. Thus, urine bilirubin may be found before serum bilirubin reaches levels high enough to cause clinical jaundice.

The lack of bilirubin in the intestinal tract is responsible for the pale stools typically associated with biliary obstruction. The cause of itching (pruritus) associated with biliary obstruction is not clear. Some believe it may be related to the accumulation of bile acids in the skin. Others suggest it may be related to the release of endogenous opioids.

Frequency

United States

The incidence of biliary obstruction is approximately 5 cases per 1000 people.

Mortality/Morbidity

The mortality and morbidity of biliary obstruction depend on the cause of the obstruction.

Race

The racial predilection depends on the cause of the biliary obstruction.

• Gallstones are the most common cause of biliary obstruction. Persons of Hispanic origin and Northern Europeans have a higher risk of gallstones compared to people from Asia and Africa.
• Native Americans (particularly Pima Indians) have an increased incidence of obesity and diabetes within their population and are especially prone to developing gallstones. Pima women have a lifetime chance of developing gallstones as high as 80%.

Sex

The sexual predilection depends on the specific cause of the biliary obstruction.

• Gallstone disease is the most common cause of biliary obstruction. Women are much more likely to develop gallstones than men. By the sixth decade, almost 25% of American women develop gallstones, with as many as 50% of women aged 75 years developing gallstones. This increased risk is likely caused by the effect of estrogen on the liver, causing it to remove more cholesterol from the blood and diverting it into the bile.
• Approximately 20% of men aged 75 years have gallstones, with more complicated disease courses occurring in those who have had cholecystectomies.

Please click here to view the full topic text: Biliary Obstruction