Gastrointestinal and Biliary System Overview

This document delves into various aspects concerning the gastrointestinal and biliary systems, particularly focusing on the biliary system's pathologies, imaging techniques, and management strategies.

Learning Outcomes

Explain the aetiology and pathogenesis of pathologies related to the biliary system.
Discuss signs and symptoms of biliary disease.
Explain the role and efficacy of various imaging modality options in diagnosing, guiding therapy and management of the biliary system.
Describe the imaging appearances of biliary pathologies on various imaging modalities.

Introduction

The liver plays several crucial roles, one of which is excretion. Bile, the primary excretory product of the liver, is typically secreted at a rate of approximately 600 mL/day. The composition of bile includes bilirubin, bile salts, lipids, electrolytes, and water. It is produced by liver cells and subsequently excreted through bile ducts into the intestine or stored within the gallbladder (Damjanov; 2017).

The biliary system encompasses bile production, storage, and secretion through the liver, gallbladder, and bile ducts. The complex ductal system that collects bile from the liver (hepatic parenchyma) and transports it to the duodenum is termed the biliary tree, which is categorized into intra- and extra-hepatic bile ducts. Variability within the biliary tree is quite common.

Functions of Bile

Bile serves two principal functions: facilitating lipid absorption and digestion, and eliminating waste products from the body. Bile secretion is regulated by the hormones cholecystokinin (CCK) and secretin (Dave et al., 2022).

CCK, secreted by the I cells in the small intestine in response to fats and proteins, prompts a contraction of the gallbladder, leading to bile travel from the cystic duct into the common bile duct. Concurrently, the sphincter of Oddi relaxes, allowing bile to enter the duodenum. Secretin further stimulates biliary and pancreatic ductal cells to secrete water and bicarbonate, enhancing bile volume entering the duodenum (Dave et al., 2022).

Cholestasis - Pathophysiology

The decrease or cessation of bile formation or flow is termed cholestasis. Factors contributing to cholestasis may include impaired canalicular secretion of bile, ductular diseases, or obstruction within the biliary tree. Causes of diminished canalicular secretion can stem from drugs, sex hormones, or inherited defects. Ductal diseases like primary biliary cirrhosis and primary sclerosing cholangitis are also contributory. Additionally, bile duct obstructions are most frequently caused by gallstones but can also result from cancers affecting the bile ducts or pancreas (Hundt et al., 2024).

Biliary Pathologies

Cholelithiasis

Cholelithiasis, or the formation of gallstones, arises from hardened deposits of digestive fluid that may develop within the gallbladder. Contributing factors include excess water reabsorption from bile, elevated cholesterol levels in bile, enhanced bile acid reabsorption, and inflammation of the gallbladder epithelium.

Acute Cholecystitis

Acute cholecystitis accounts for the most common cause of right upper quadrant (RUQ) pain, with approximately 90-95% of cases linked to gallstones, while acalculous conditions account for 5-10%. Acute cholecystitis arises from cystic duct blockage, leading to inflammation of the gallbladder.

Chronic Cholecystitis

Chronic cholecystitis is a prolonged condition triggered by mechanical or functional dysfunctions in gallbladder emptying, which can lead to acute cholecystitis. There are two forms: calculous (associated with gallstones) and acalculous (without gallstones). Most chronic cases involve cholelithiasis, typically stemming from recurrent acute cholecystitis episodes or chronic irritation due to gallstones (Jones et al., 2023).

Choledocholithiasis

This condition refers to the presence of gallstones within the common bile duct, usually presenting with RUQ abdominal pain. The pain pattern and timing can vary per patient (McNicholl et al., 2023).

Cholangitis

Acute cholangitis, or ascending cholangitis, is a serious condition arising from a bacterial infection in the biliary tree. A diagnostic delay can result in septic shock. Choledocholithiasis commonly leads to this condition, as stones in the common bile duct can cause partial or complete obstruction of the biliary system. Clinical presentation, abnormal lab results, and imaging studies indicating infection or obstruction assist in diagnosis (Virgile and Marathi, 2023).

Epidemiology

Gallstone disease is prevalent, with 10-20% of the global population experiencing gallstones in their lifetime, and incidence increases with age. Despite this, around 80% of cases are asymptomatic. Notably, over one-quarter of women older than 60 have gallstones, while obesity increases risk factors, particularly among women due to higher biliary cholesterol secretion.

Signs and Symptoms

Pruritus
Dark urine
Pale stools
Steatorrhea
Possible association with vitamin K deficiency
Murphy’s sign
RUQ mass, pain, or tenderness
Fever (may be normal in chronic cholecystitis)
Elevated CRP (may be normal in chronic cholecystitis)
Abnormal WBC count (may be normal in chronic cholecystitis)

Diagnosis

Blood tests play a critical role in identifying and evaluating biliary tract disorders, with a comprehensive metabolic panel (CMP) assessing key liver enzymes and bilirubin levels (Dave et al., 2022).

Imaging Techniques

CXR

Chest X-ray may be used to exclude thoracic causes of pain.

Ultrasound

Ultrasound is the primary imaging technique recommended for suspected acute cholecystitis and is more sensitive than CT for gallstone detection. A positive sonographic Murphy sign indicates gallbladder tenderness upon probe application.

Endoscopic Ultrasound

This method locates bile duct stones and identifies pancreatic or biliary cancers effectively.

CT Cholangiogram

CT cholangiography uses contrast to visualize the biliary tree, making it useful for identifying bile leaks or retained gallstones.

ERCP

Endoscopic Retrograde Cholangiopancreatography (ERCP) not only assesses the bile and pancreatic ducts but also facilitates stone removal and pressure measurement in the sphincter of Oddi. It typically follows diagnostic imaging like CT or MRCP (Dave et al., 2022).

MRCP

Magnetic Resonance Cholangiopancreatography (MRCP) is a non-invasive MRI method that produces images of the bile and pancreatic ducts without requiring endoscopy, thus lacking the ability to remove stones or treat abnormalities detected (Dave et al., 2022).

HIDA Scan

Also known as cholescintigraphy, the HIDA scan serves as a confirmatory test for uncomplicated cholecystitis when ultrasound findings are inconclusive. A radioactive tracer is injected, allowing for the assessment of cystic duct patency (Dave et al., 2022).

Patient Management/Treatment

The preferred management approach for cholecystitis is laparoscopic cholecystectomy due to its low morbidity and mortality rates coupled with rapid recovery.

Questions and Further Reading

Students are encouraged to address any queries during class or submit them on the discussion board.

Suggested Revision Question

Compare and contrast the imaging pathways for acute versus chronic cholecystitis.

References

Damjanov, I. (2017) Pathology for the health professions (5th ed.). Maryland Heights, Mo.: Elsevier/Saunders.
Dave HD, Shumway KR, Al Obaidi NM. Physiology, Biliary. [Updated 2022 Dec 15]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537107/
Hundt M, Basit H, John S. Physiology, Bile Secretion. [Updated 2022 Sep 26]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470209/
Jones MW, Gnanapandithan K, Panneerselvam D, et al. Chronic Cholecystitis. [Updated 2023 Aug 8]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470236/
McNicoll CF, Pastorino A, Farooq U, et al. Choledocholithiasis. [Updated 2023 Jul 10]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441961/
Virgile J, Marathi R. Cholangitis. [Updated 2023 Jul 3]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK558946/

Comprehensive Overview of the Biliary System and Its Pathologies

Comprehensive Overview of the Biliary System and Its Pathologies