Ultrasound (US) has high specificity and sensitivity, and it should be performed first for patients with suspicion of biliary tract cancer. However, the complicated anatomy in addition to the gas images makes it difficult to delineate the entire extrahepatic bile duct (EHBD). The keys to depiction of EHBD are the "J" shape manipulation in the left lateral decubitus position and the use of magnified images with high-frequency transducers. Furthermore, indirect findings such as gallbladder (GB) distension, BD dilatation, and debris echo in the GB and BD are also important for detecting occult lesions, particularly in the ampullary region of Vater. For the differential diagnosis of BD wall thickening, the spreading pattern in the long and short axial directions should be assessed first. Then, the characteristics of the innermost hyperechoic layer (IHL) and outermost hyperechoic layer (OHL) should be evaluated. Asymmetrical wall thickening, absence of IHL, and presence of irregularity or discontinuity in OHL are characteristic patterns of cholangiocarcinoma (CCA). Because CCA is the most common BD polypoid lesion, it is important to diagnose tumor extension and depth invasion in addition to differential diagnosis. Nodular-type CCA is usually hypoechoic and more likely to invade vertically. In contrast, papillary-type CCA is often hyperechoic and extends laterally. Contrast‑enhanced US may be useful for evaluating these findings. However, if the possibility of CCA cannot be ruled out or a definitive diagnosis is needed, a transpapillary biopsy or endoscopic US-guided tissue acquisition should be considered.
Advances in next-generation sequencing have made comprehensive genomic profiling (CGP) using tumor tissue specimens and liquid biopsy using blood samples feasible in routine clinical practice. In the context of pancreaticobiliary cancer, it is necessary to consider CGP in formulating individualized treatment strategies. Performing CGP with tumor tissue specimens requires a sufficient number of high-quality samples. EUS-guided tissue acquisition (EUS-TA) is expected to play a significant role in this regard, and endosonographers need to address this role. Here, we review the current status of EUS-TA for CGP focusing on pancreatic cancer and biliary tract cancer.
Magnetic resonance imaging (MRI)-detected lesions are often category 2 or 3 lesions on initial ultrasound examination. In addition, in the case of new non-mass lesions detected on MRI, one would expect to find lesions with ductal dilatation with minimal secretory accumulation, single short lesions with ductal dilatation, cyst-like lesions less than 5 mm in size, mammary gland-like lesions less than 8 mm in size, and very indistinct lesions. Detection is expected to be even more difficult. Currently, there are no clear uniform criteria for the indication of second-look ultrasonography (US) for MRI-detected lesions, so it is not possible to make a general comparison, but recent studies have indicated that the ratio of mass to non-mass MRI-detected lesions is 7:3. And it has been pointed out that the percentage of malignancy is about 30% for each. Before about 2012, the US detection rate was about 70%, and MRI-guided biopsies of undetected lesions showed a small percentage of malignant lesions. Therefore, some observers believe that lesions not detected on US should be followed up, while others believe that MRI-guided biopsy should be performed. Recently, however, the use of surrounding anatomical structures as landmarks for second-look US has increased the detection rate to as high as 87-99%, and the percentage of malignancy remains the same. In addition, recent surveillance of high-risk breast cancer requires careful management of MRI-detected lesions. In this review, we will discuss the literature on MRI-detected lesions and describe ultrasound techniques to accurately detect small lesions and reliably reveal pale lesions based on their structural differences from their surroundings.
