Cholangiocarcinomas are extremely rare cancers that occur in the epithelial cells of the intrahepatic or extrahepatic bile duct. Magnetic resonance imaging and nuclear imaging are two of the main imaging modalities used for diagnosing and monitoring them.
The overwhelming majority of cholangiocarcinoma cases are histologically sclerosing adenocarcinoma. The main method of disease classification is based on where it is located anatomically.
“Cholangiocarcinoma is diagnosed via a combination of clinical symptoms, imaging manifestations, biochemical features, and histological examinations, and imaging plays a crucial role,“ Liu and colleagues wrote in a review recently published in Insights into Imaging. “Cholangiocarcinoma, often insidious and sometimes without overt symptoms for years, is a difficult disease to diagnose early.“
Read more about cholangiocarcinoma etiology
It is impossible to discuss the diagnosis of cholangiocarcinoma today without a heavy mention of the imaging diagnostic tools needed. Without modern imaging tools—made available and refined over the last few decades— there would likely be no discussion of cholangiocarcinoma at all (at least while the patient is still alive). Cholangiocarcinoma would have remained one of those diseases that suddenly presents with symptoms (relating to bile duct obstruction) at an advanced stage, of which the only therapeutic option is palliative care.
Today, hepatology is a different field of medicine altogether. Among the various medical disciplines, hepatology is arguably equipped with the most advanced selection of imaging tools and devices. With these tools, a few of which we will discuss in this article, some areas of hepatic medicine will increasingly resemble removing blockage from a drain: the work of a well-skilled plumber.
The Benefits of MRI
Azizaddini and Mani argued that MRI represents the best imaging modality for the liver because of the following:
- The lack of ionizing radiation.
- High cross-sectional resolution.
- The availability of hepatocyte-specific and extracellular contrast agents.
- The yielding of high-quality information about diffuse liver lesions and focal liver lesions.
- Precise visualization of bile ducts and adjacent structures.
Yang and Shu agree with this assessment. They wrote, “At present, MRI is considered the most accurate and least invasive imaging modality for the assessment of [cholangiocarcinoma].”
In addition, diffusion-weighted imaging (DWI) has been known to boost the visibility of hepatic lesions, thus increasing the diagnostic sensitivity of MRI for cholangiocarcinoma. DWI may also serve as an independent tool for evaluating histopathological findings and predicting the prognosis of cholangiocarcinoma patients.
The main limitation to MRI is the long scanning time. During the duration of the scan, patients need to remain as still as possible in order for the highest-quality images to be secured. In addition, some patients are contraindicated for MRI, such as those with metal implants or severe claustrophobia.
The Powers of Nuclear Imaging
Nuclear imaging is an imaging modality that reveals physiological and pathological activity via the detection of the metabolic processes of tracers with radionuclides. It allows physicians to better diagnose liver tumors and monitor their progress.
What do researchers recognize as the best radiotracer for detecting and diagnosing cholangiocarcinoma today?
“To date, fluorine-18 fluorodeoxyglucose (18F-FDG) PET/CT has been widely used to evaluate multiple malignancies,“ Yang and Shu wrote. “Various studies have indicated that 18F-FDG PET/CT plays an important role in assessing [cholangiocarcinoma] and have estimated the efficiency to detect and diagnose [cholangiocarcinoma] at sensitivities of 84%– 94% and specificities of 79.3%-100%.”
Liu and colleagues reported similar findings on the high sensitivity and specificity of 18F-FDG as a radiotracer for cholangiocarcinoma. 18F-FDG has a higher sensitivity and specificity for suspected intrahepatic cholangiocarcinoma (95% and 100% respectively) compared to suspected extrahepatic cholangiocarcinoma (69.2% and 66.7% respectively).
Read more about cholangiocarcinoma diagnosis
Another benefit of 18F-FDG PET/CT is that it can be used to evaluate tumor spread prior to surgery. Studies indicate that 18F-FDG PET/CT has a 58.8% sensitivity for primary tumors, 41.7%-64.7% sensitivity for lymph node metastasis, and 41.7%-55.6% sensitivity for distant metastasis. This means that it can be a highly useful tool in helping surgeons decide on the best surgical approach for their patients.
Although nuclear imaging has high sensitivity and specificity for cholangiocarcinoma, its main downside is that it has a high false-positive rate due to its flagging of any focal hypermetabolism area. Its sensitivity also drops with lesions smaller than 1 cm in size.
Despite the advantages of MRI and nuclear imaging, neither of these imaging tools is likely to be the first used when a patient presents with hepatic symptoms.
“The first imaging modality to choose to evaluate liver pathology depends on the patient’s clinical situation, availability of different modalities, technician, and physician familiarity with the test,” Azizaddini and Mani wrote. “[Ultrasound] and CT remain the first imaging modality to assess the diffuse and focal liver lesion for screening and characterization.”
There are benefits and downsides to each imaging modality (as well as their costs), so a wise physician should only order an imaging test when there is a clinical imperative to do so. When used in a complementary fashion, medical imaging tools can guide physicians to make better decisions for their patients.
Azizaddini S, Mani N. Liver imaging. In: StatPearls [Internet]. StatPearls Publishing; 2021. Accessed January 26, 2022.
Liu J, Ren WX, Shu J. Multimodal molecular imaging evaluation for early diagnosis and prognosis of cholangiocarcinoma. Insights Imaging. Published online January 20, 2022. doi:10.1186/s13244-021-01147-7
Yang CM, Shu J. Cholangiocarcinoma evaluation via imaging and artificial intelligence. Oncology. 2021;99(2):72-83. doi:10.1159/000507449