There is an inside joke within the medical fraternity about the enthusiasm that surgeons exude in favor of invasive treatment during multidisciplinary meetings. The characterization is that while invasive treatment is usually seen as a last resort by physicians that belong to other disciplines, surgeons often see it as first-line therapy.
Unfair (or perhaps sometimes fair) characterizations aside, invasive imaging and treatment do come with both a hefty price and a heavy cost. In other words, they are usually very expensive and unfortunately carry a high risk of postprocedural infection, which can result in mortality for patients who are already immunocompromised.
This is why research is continuously being conducted into existing noninvasive imaging modalities, such as ultrasound and magnetic resonance imaging (MRI). Medical researchers are constantly looking for new clues that can provide valuable insights into a disease before surgery is initiated.
A team of Chinese researchers from the Department of Radiology at Sichuan University West China Hospital in Chengdu conducted a literature review on the role of noninvasive imaging in the evaluation of intrahepatic cholangiocarcinoma (ICC). Their article as published in Expert Review of Gastroenterology & Hepatology will form the foundation of our discussion in this article.
Diagnosis of ICC
ICC is the second most common cholangiocarcinoma after hepatocellular cholangiocarcinoma. Histopathological examination remains the gold standard for ICC diagnosis. One of the most distinctive histological findings in ICC is desmoplastic stroma, driven by proliferating fibroblasts in the tumor microenvironment.
Read more about cholangiocarcinoma etiology
Despite histopathological evidence being the gold standard of diagnosis, only a minority of ICC patients are diagnosed this way. In the vast majority of cases, physicians rely heavily on noninvasive imaging modalities for tumor diagnosis and assessment. The authors of the study stated, “Moreover, radiomics, a method to assess tumors and their microenvironment in their entirety, has shown potential for improving diagnostic and prognostic accuracies and guiding individualized treatment of ICC in the era of precision medicine by assessing the carcinoma heterogeneity and predicting biological behavior and genetic variation.”
Noninvasive Imaging Modalities
Let us take a look at some noninvasive imaging modalities available for ICC and examine their usefulness. Ultrasound is, of course, one of the cheapest and most widely available imaging modalities in hospitals across the world. It is favored as first-line imaging because it does not use ionizing radiation or cause nephrotoxicity. In ICC, it has 2 main benefits: it allows physicians to identify the cause and site of bile duct obstruction, and it allows for real-time visualization of the circulation in and around the tumor. The main disadvantage of ultrasound is that it has a high false-positive rate for tumors that are 5 cm in size or smaller.
Computed tomography (CT) is undoubtedly one of the best imaging modalities to visualize vascular anatomy. In addition, CT gives physicians the ability to evaluate the tumor in terms of vascular invasion, the involvement of lymph nodes, and metastases (if any). However, besides the risk of ionizing radiation, one of the main disadvantages of CT imaging in the context of ICC is that it is largely unable to detect longitudinal tumors spread along the bile ducts.
Read more about cholangiocarcinoma diagnosis
MRI allows physicians to have an unparalleled view of the biliary ducts that are proximal to any detected obstruction. Because of its superior soft-tissue contrast ability, MRI is better able to detect longitudinal tumors spread along bile ducts than CT. However, it has limited specificity in patients who have a history of chronic liver cirrhosis or a tumor size smaller than 3 cm.
Positron emission tomography (PET) scans are excellent for quantifying the glucose metabolism potential of tumors. “18 F-FDG PET plays a crucial function in the candidate selection for surgery due to its ability to assess the local tumor extent, the presence of lymph node metastasis, and distant metastasis,” the authors of the review explained. However, it is important to note that while PET may detect the presence of metastasis, it is not useful for excluding it.
Assessing Prognosis and Treatment Response
Aside from diagnosing and characterizing ICC, the imaging modalities mentioned above can also be used, in different degrees, to assess prognosis and treatment response. For example, arterial hypoenhancement on MRI or CT is associated with a poorer prognosis. This is because arterial hypoenhancement in ICC is likely caused by rich desmoplastic stroma.
With regards to assessing treatment response, imaging is indispensable as a tool for decision-making. There exists a number of post-treatment imaging criteria that are used to evaluate treatment response, including the Response Evaluation Criteria in Solid Tumors (RECIST), Choi criteria, and PET Response Criteria in Solid Tumors (PERCIST 1.0).
The imaging modalities for ICC discussed in this article are incredibly common, but continuous research demonstrates time and again that there is still much to discover and learn about their abilities to yield important information regarding diagnosis, disease progression, and prognosis.
As Tapper and Lok so eloquently stated in their review of liver imaging and biopsy, “Noninvasive tests have not replaced liver biopsy but have sharply reduced the need for it. This shift has greatly improved our ability to care for patients with liver diseases.” They added, “However, the limitations of these noninvasive tests must be recognized. Liver biopsy will continue to have a role in diagnosing some liver diseases, resolving indeterminate stages of fibrosis, and addressing specific research questions.”
Li Q, Che F, Wei Y, Jiang HY, Zhang Y, Song B. Role of noninvasive imaging in the evaluation of intrahepatic cholangiocarcinoma: from diagnosis and prognosis to treatment response. Exp Rev Gastroenterol Hepatol. Published online September 1, 2021. doi:10.1080/17474124.2021.1974294
Tapper EB, Lok ASF. Use of liver imaging and biopsy in clinical practice. N Engl J Med. 2017;377(8):756-768. doi:10.1056/NEJMra1610570