Biliary Tree Pathophysiology & Investigations

Laboratory Investigations in Biliary Tree Pathophysiology

The laboratory investigation will show us. 

• Raised bilirubin and raised ALP (alkaline phosphates) are suggestive of the cholestatic process.
• Cholestasis means there is an obstruction.
• Raised serum transaminases are suggestive of hepatocyte pathology.

This all can be due to Hyperbilirubinemia, or jaundice is of two types:

1. Conjugated Hyperbilirubinemia
   • The cause of conjugated hyperbilirubinemia is obstruction. Hyperbilirubinaemia, which is conjugated to obstructive jaundice, is identifiable in these organs:
     • Frenulum: The first structure to be checked is the frenulum.
     • Sclera: The bilirubin level is ≥ 2.5 mg/dl when obstructive jaundice is observed in the sclera.
     • Skin: The bilirubin level should be >5 mg/dl when obstructive jaundice is observed in the skin.
2. Unconjugated Hyperbilirubinemia
   • The causes of unconjugated hyperbilirubinemia can be any one of the following:
     • Increased synthesis of unconjugated hyperbilirubinemia in patients in whom hemolyses occur
     • Impaired hepatocyte uptake of unconjugated bilirubin
     • Decreased intracellular conjugation

There are some specific imaging techniques that are used to check for any biliary tree pathophysiologies. 

Plain X-ray

• 90% of gallstones: Radiolucent
• 90% of renal stones: Radiopaque
• 80% of salivary gland stones : Radiopaque

Ultrasound 

It differentiates medical and surgical jaundice. Ultrasound is the initial investigation of choice for the evaluation of jaundice or symptoms with biliary disease or for patients with dilated common bile duct (CBD) with jaundice. The jaundice that occurs because of obstruction or blockage of excretion is called surgical jaundice. Dilated CBD with jaundice can be painful, or it can be painless. It is painful whenever the obstruction is due to a stone that is an acute obstruction. Because of this, there is stretching, which leads to the activation of pain fibers. Whenever it's because of a tumor, it is painless. Ultrasound is the investigation of choice for the diagnosis of :

• Gallstone
• Acute cholecystitis
• Acute acalculous cholecystitis
• Chronic cholecystitis
• Sometimes, ultrasound can identify even the causes of obstructive jaundice by visualizing CBD stones and sometimes by cholangiocarcinoma.

Gall Bladder Polyp USG

Gall bladder polyps are fixed, and they don’t change as the patient's position changes. This can be visualized using USG.

Sludge on USG

If the patient has sludge, it can be identified on USG. Sludge moves slowly and does not have a sharp echogenic pattern of cause. Therefore, Ultrasound is the investigation of choice for the diagnosis of acute cholecystitis. It can also diagnose the porcelain gallbladder, in which the wall is calcified.

USG in Acute Cholecystitis

In acute cholecystitis, The patient will have gallbladder thickening. The thickness of the gallbladder wall should be more than 4 mm, and there should be the presence of pericholecystic fluid. Ultrasound is the preferred diagnosis for acute cholecystitis. Porcelain gallbladder, also called calcified gallbladder since the wall is calcified, appears as an echogenic focus in the entire gallbladder wall. Apart from this, there is also acoustic shadowing.

HIDA (Hepatic Imindiacetic Acid) Scan

The gold standard of investigation is the HIDA (Hepatic iminodiacetic acid) Scan for acute cholecystitis. In HIDA scan: Imino diacetic acid is processed in the liver before being secreted in the bile, bile flow, gallbladder, bile duct, and small intestine. If the patient has a normal HIDA scan, there is tracer in the gallbladder (GB), CBD, and small intestine. In acute cholecystitis, visualization of the liver, CBD, and small intestine whereas the gallbladder is not visualized as there is obstruction because of a stone in the cystic duct, the GB is not visualized. So the failure of GB filling even after 2 hours of injection is suggestive of obstruction of the cystic duct and is diagnosed as acute cholecystitis.

The other role of the HIDA scan is to identify obstruction of the biliary tree, a bile leak, or Gall bladder function. By injecting cholecystokinin during the scan, the gallbladder contracts and gallbladder content is ejected. That means the scan will document the gallbladder's physiological function. It is also useful in patients with biliary tract pain without stones, whose cause can be biliary dyskinesia.

Role of CT in the Biliary Tract Pathologies

CT has better anatomical delineation than ultrasound. It is used to identify the cause and site of biliary obstruction.

MRI/MRCP (Magnetic Resonance Cholangiopancreatography)

It is the choice of investigation for CBD stones, choledochal cysts, biliary strictures/primary sclerosing, and cholangitis. MRCP is investigation of choice for diagnosis of CBD stone. ERCP is diagnostic and therapeutic for CBD stone so it is considered a gold standard. MRI/MRCP: MRI uses water in the bile to delineate the biliary tree, and it provides a superior anatomical definition of the intrahepatic and extrahepatic biliary trees as well as the pancreatic duct.

ERCP (Endoscopic Retrograde Cholangiopancreatography)

It is used when some intervention is required and is the gold-standard investigation. ERCP is used for obstruction. It is used in Malignant obstruction: as the endoscope is used, tissue samples can be taken by biopsy. If there is obstruction, a stent is inserted, and decompression of obstruction is done by stenting. 

In Choledocholithiasis, the stone is removed using ERCP. The maximum size of the stone that can be removed by ERCP is 1.5 cm.

In conclusion, MRCP is the investigation of choice for most biliary tract pathology because it is an excellent modality for cross-sectional imaging of the biliary tree, including CBD stones, choledochal cysts, biliary strictures, and primary sclerosing cholangitis.

Percutaneous Transhepatic Cholangiography (PTC) 

In PTC, the needle is passed directly into the liver, percutaneously in one of the biliary radicals, and the dye is injected. As it is injected, the biliary tree is visualized; therefore, it is called cholangiography. It is both a diagnostic and therapeutic procedure.

Whatever interventions are done with ERCP in the distal part of the bile duct All these interventions are performed in the proximal region in PTC. It allows the insertion of a transhepatic catheter for drainage or for biopsy. In intrahepatic biliary disease, it can decompress the biliary obstruction. It is used in stent intervention. As the dye is injected, it provides complete information or anatomical information about biliary reconstruction.

Intra-Operative Cholangiography 

Intra - operative cholangiography is used to delineate anomalous biliary anatomy. It can identify choledocholithiasis. It can guide biliary reconstruction. Routine use of intraoperative cholangiography does not significantly reduce the injury to the biliary tree during cholecystectomy.

Indication for selective use of  cholangiography: 

• Pain on the day of operation: It means there is an obstruction. Usually, there is pain due to obstruction.
• Abnormal liver function test(LFT)
• Anomalous or confusing biliary anatomy
• Alteration in anatomy that precludes the ability to perform ERCP after cholecystectomy
• Dilated biliary tree: indirect evidence of obstruction of the bile duct
• If there is pre-operative suspicion of choledocholithiasis, perform intra-operative geography, and if stone is there, stone is removed.

Endoscopic Ultrasound

It is valuable in the assessment of distal CBD and ampulla. It is most helpful in assessing tumors for invasion into vascular structures. There are two types of endoscopes.

1. Radial eco-endoscope: useful for providing tomographic evaluation
2. Linear eco-endoscopes: they are used to guide interventions, such as if you are planning a needle biopsy under ultrasound guidance.

FDG PET (Fluoro-Deoxyglucose Positron Emission Tomography)

FDG is given to the patient, and this radioactive glucose is taken by the most hyperactive cells in the body. Malignant cells are one of the most hyperactive cells. After the body is scanned, the area where there is maximum uptake is those other areas of malignancy or metastasis, or if it is done after surgery, those areas are areas of recurrence.

Uses of FDG PET

• It is used to differentiate between benign and malignant lesions.
• Detect the recurrence post-operatively.
• It is used to identify metastatic disease.

Disadvantage of FDG PET

It is incapable of demonstrating carcinomatosis and the high metabolism of the immune system. FDG PET has limited value in the setting of infection or inflammation because, when there is infection or inflammation, those cells are also hyperactive.

Bacteriology Of Biliary Tree Pathophysiology

The most common organism responsible for infection in biliary tree diseases like cholangitis is E. coli, followed by Klebsiella. Prophylactic antibiotics are used in some cases or for patients who are undergoing interventions. Intervention means an ERCP or PCT. First or second-generation cephalosporins or fluoroquinolones are used. For elective laparoscopic cholecystectomy for biliary colic, antibiotic prophylaxis is not necessary. If the patient has a suspected or documented infection of the biliary tree, like acute cholecystitis or ascending cholangitis, antibiotics are used.

Also Read: Pyogenic Liver Abscess : Pathology, Diagnosis, Treatment

Frequently Asked Questions

Q. What should be the level of bilirubin when you can identify the Icterus in the sclera?

Answer. The bilirubin level is ≥ 2.5 mg/dl.

Q. What should be the level of bilirubin whenever you can identify the Icterus in the skin?

Answer. The bilirubin level should be >5 mg/dl.

Q. Are 90% of gallstones radiolucent or radio-opaque?

Answer. Ninety percent of gallstones are radiolucent, but 90 percent of kidney stones are radio-opaque, and 80 percent of salivary gland stones are radio-opaque. This means that gallstones are not regularly seen on plane X-rays, and even if they are sometimes seen, visualization of gallstones on the X-ray doesn't change the therapy.

Q. What is the Role of ultrasound in biliary tree pathophysiology?

Answer. Ultrasound differentiates medical and surgical jaundice.

Q: How do to identify a gall bladder polyp?

Answer. The polyp is fixed, and it doesn’t change as the position of the patient changes the position.

Q. How do to identify if a patient is having sludge?

Answer. Sludge moves slowly, and it does not have a sharp echogenic pattern of cause.

Ultrasound is the investigation of choice for the diagnosis of acute cholecystitis, and secondly, it can also diagnose the porcelain gallbladder, in which the wall is calcified.

Q. What are the findings in acute cholecystitis?

Answer. The patient will have gallbladder thickening. The thickness of the gallbladder wall should be more than 4 mm, and there should be the presence of pericholecystic fluid.

Q. What is the role of CT in the biliary tract?

Answer. CT has better anatomical delineation than ultrasound. It is used to identify the cause and site of biliary obstruction.

Also Read: Colorectal Polyps : Types, Neoplastic Polyps

Hope you found this blog helpful for your GIT, Hepatobiliary and Pancreatic Surgery preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.