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The biliary tree is made up of channels that collect bile from the hepatic parenchyma and transport it to the duodenum. It is divided into the intrahepatic and extrahepatic ducts. The clinical organization in most of the population is as follows:
- Bile canaliculi unite to form segmental bile ducts that drain liver segments. These segmental ducts unite as follows:
- Segments VI and VII form the right posterior duct.
- Segments V and VIII form the right anterior duct.
- Segments II, III and IV unite to form the left hepatic duct.
- The right hepatic duct is formed by the joining of the right anterior and posterior ducts.
- The right and left hepatic ducts unite to form the common hepatic duct that joins the cystic duct to form the common bile duct. The common bile duct crosses posterior to the duodenum and pancreas to unite with the main pancreatic duct and form the ampulla of Vater that drains into the duodenum.
Traumatic Biliary Leaks
The biliary tract can be injured in abdominal trauma but this is usually rare. The estimated prevalence of biliary tract injuries in patients who sustain a significant blunt hepatic trauma is around 2.8%.
Biliary tract injuries are usually associated with hepatic, splenic and/or duodenal injuries. The most commonly injured part of the biliary tract is the gallbladder. The intrahepatic biliary system is the least common part of the biliary tract to be injured in blunt abdominal trauma.
Patients with intrahepatic biliary system traumatic injuries also have hepatic parenchymal injuries. The risk of intrahepatic biliary system injury seems to be unrelated to the severity of hepatic parenchymal injury or the American Association for Surgery of Trauma liver injury grade.
Imaging Studies in Patients with Traumatic Intrahepatic Biliary System Injuries
Computed Tomography Scan
This is the imaging modality of choice in trauma set-ups. A patient with a blunt abdominal trauma usually undergoes a multidetector computed tomography scan of the abdomen to look for solid organ injuries and grade such injuries. When there is evidence of hepatic parenchymal injury, the risk of intrahepatic biliary system injury and leak becomes higher. Unfortunately, the computed tomography findings in patients with biliary injuries are usually non-specific.
In some patients, the main imaging finding on computed tomography scans of the liver is intrahepatic contrast accumulation. These small intrahepatic fluid collections are believed to originate from focal bile leaks which can later develop into a biloma. Patients with intrahepatic fluid collections and extravasation of contrast on delayed imaging usually have a high-grade liver injury.
Ultrasonography can also be used in the evaluation of the traumatic liver and intrahepatic biliary system. The main goal of ultrasonography is to evaluate the progress and evolution of a biloma rather than to exclude or grade hepatic injuries. Ultrasound-guided drainage of the biloma might be performed if the collection is growing.
Hepatobiliary scintigraphy can be also used in patients with suspected intrahepatic or extrahepatic biliary tract injuries. Contained intrahepatic leaks can be easily identified on hepatobiliary scintigraphy.
Magnetic resonance cholangiopancreatography
The most sensitive and specific imaging modality for intrahepatic biliary system traumatic injuries and leaks is magnetic resonance cholangiopancreatography with a hepatobiliary contrast. The images produced with this technique can help in evaluating the anatomy of the biliary tract from the intrahepatic part to the gallbladder to the extrahepatic part and intrapancreatic portion.
Magnetic Resonance Cholangiopancreatography
- Heavily T2 weighted sequences performed without contrast
- Very helpful in determining cause and level of obstruction
Intrahepatic cholangiocarcinoma arises from the intrahepatic portion of the biliary tract and are considered as the second most common intrahepatic primary tumor. They arise from the biliary epithelium of mucin-producing cells, known as cylindrical cells, which are found within the segmental bile ducts or from cuboidal cholangiocytes which do not produce mucin.
These tumors are very invasive and usually have areas of necrosis, fibrosis and mucin on histopathology. Intrahepatic cholangiocarcinoma can spread via the biliary system, venous system or lymphatic system.
The clinical presentation of intrahepatic cholangiocarcinoma is non-specific and consists of abdominal pain, weight loss, jaundice and night sweats.
Imaging Studies in Intrahepatic Cholangiocarcinoma
The main imaging modalities used in the radiographic evaluation of intrahepatic cholangiocarcinoma are ultrasonography, computed tomography, magnetic resonance imaging and positron emission tomography. Each imaging modality has its own strength points, weaknesses and indications.
Ultrasonography in Intrahepatic Cholangiocarcinoma
Ultrasonography is usually the first imaging modality used in any patient complaining of non-specific abdominal symptoms such as pain and indigestion.
An intrahepatic cholangiocarcinoma is usually hyperechoic. These tumors tend to be homogenous and they can resemble hepatocellular carcinoma. Contrast enhanced ultrasound might show washout within intrahepatic cholangiocarcinoma similar to what you would see with hepatocellular carcinoma.
Computed Tomography in Intrahepatic Cholangiocarcinoma
Intrahepatic cholangiocarcinoma can be infiltrative and they usually do not have a capsule which can differentiate them from hepatocellular carcinoma. The lesions appear hypoattenuating on non-enhanced computed tomography.
When contrast is used, intrahepatic cholangiocarcinoma shows enhancement only on delayed imaging series, but not in the arterial or portal venous phase images. When necrosis and mucin is extensive in the center of the tumor, the center of the tumor remains hypodense despite contrast administration. A recent study has found that tumors that show enhancement of more than two thirds of the tumor’s bulk are usually associated with a worse prognosis.
Magnetic Resonance Imaging in Intrahepatic Cholangiocarcinoma
Intrahepatic cholangiocarcinoma is usually hypointense on T1-weighted images. They can be hypointense, iso-intense or hyperintense on T2-weighted images. Mucin-producing tumors are usually hyperintense on T2-weighted images, whereas tumors with extensive fibrosis are typically hypointense on T2-weighted images.
The administration of intravenous gadolinium typically shows early peripheral enhancement, followed by delayed progressive central enhancement. Hepatobiliary specific contrast agents can be used to better understand the extent and margins of the intrahepatic cholangiocarcinoma.
Hepatocytes typically take more contrast compared to the biliary cells; therefore, a tumor that arises from biliary epithelial cells, such as a cholangiocarcinoma, is expected to be hypointense compared to the surrounding hepatic tissue when a hepatobiliary specific contrast agent is used.
Positron Emission Tomography
The main purpose of this imaging technique is to identify occult microscopic metastases. Tumor cells are expected to be more metabolically active, hence take more glucose; therefore, tumors that arise from the biliary epithelium are expected to appear as hypermetabolic regions. Unfortunately, benign biliary tumors, such as intrahepatic biliary adenoma, are also metabolically active.
Intrahepatic Biliary Adenoma
Intrahepatic biliary adenomas are rare benign biliary epithelial tumors that account for about 1% of all primary liver tumors. They are usually an incidental finding and do not cause any symptoms.
Imaging Studies in Intrahepatic Biliary Adenoma
Intrahepatic biliary adenomas are typically found incidentally on an ultrasound indicated for another problem. In most cases, you will encounter a patient with an intrahepatic biliary adenoma for further evaluation of a newly identified hepatic mass. The main goal of further imaging is to confirm the benign nature of the lesion.
Computed tomography scans
On computed tomography scans, these lesions are usually very well-defined and are small in size. They are typically of low-intensity on un-enhanced computed tomography. When contrast is used, these benign tumors typically show heterogenous enhancement with central cystic changes.
Because these tumors are very well-defined, they are unlikely to be malignant and therefore a wait-and-see approach can be followed. A repeat computed tomography scan at two months and six months is recommended to check for any size changes. A benign intrahepatic biliary adenoma is expected to show no growth over this short period or very minimal growth. If the tumor shows slight growth, it is advisable to go for hepatobiliary contrast enhanced magnetic resonance imaging.
Contrast enhanced magnetic resonance imaging
Hepatobiliary contrast enhanced magnetic resonance imaging typically shows a hypointense lesion on T1 pre-contrast, heterogenous enhancement and a hypointense lesion in contrast to the surrounding hepatic tissue after the administration of the contrast agent.
Unfortunately, these findings are the same one would expect in a cholangiocarcinoma except for the lack of invasiveness, infiltrative nature, and irregularity which are seen in malignant lesions. Regardless, most patients opt to go for surgical removal of the lesion with a hepatic segmentectomy. Once the lesion is removed, a biopsy study can then confirm the diagnosis. If the diagnosis was confirmed to be a benign intrahepatic biliary adenoma, further follow-up and treatment is usually not needed.