Contrast Enhanced Endoscopic Ultrasound Imaging for Gastrointestinal Subepithelial Tumors

Subepithelial tumors are divided into benign subepithelial and potentially malignant gastrointestinal stromal tumors. It is difficult to distinguish between these tumor types. Contrast-enhanced harmonic endoscopic ultrasound is reportedly useful for diagnosing subepithelial tumors, can be safely and easily performed by understanding the principle and method, and can be used to distinguish between tumor types with high sensitivity on the basis of differences in contrast effect. The generated image shows a hyper-enhancement pattern in gastrointestinal stromal tumors (sensitivity, 78%–100%; specificity, 60%–100%; accuracy, 60%–100%) and hypo-enhancement pattern in benign subepithelial tumors. Contrast-enhanced harmonic endoscopic ultrasound can be used to estimate the malignancy potential of gastrointestinal stromal tumors by evaluating the uniformity of the contrast and the blood vessels inside the tumor, with abnormal intra-tumor blood vessels, heterogeneous enhancement, and non-enhancing spots suggesting malignancy. Contrast-enhanced harmonic endoscopic ultrasound has a higher sensitivity than other imaging modalities for the detection of vascularity within gastrointestinal stromal tumors. Additionally, it has been reported that treatment effects can be estimated by evaluating the blood flow in the gastrointestinal stromal tumor before and after treatment with tyrosine kinase inhibitors using contrast-enhanced ultrasound. However, there will be subjective-bias and the results depends on the performer’s skill.

Clinical role of contrast-enhanced harmonic endoscopic ultrasound in differentiating pancreatic solid lesions

Accurate diagnosis of pancreatic solid lesions is often difficult using conventional imaging modalities. With the recent introduction of contrast-enhanced harmonic endoscopic ultrasound (CEH-EUS), it is now possible to evaluate the microvascular environment and dynamic enhancement of a variety of pancreatic lesions. With CEH-EUS, three patterns of pancreatic lesion enhancement compared with the normal pancreatic tissue (fast, simultaneous, or slow), two washout patterns (fast or slow) and two distribution patterns (homogeneous, inhomogeneous) can be described. By evaluating the microvasculature, enhancement speed, and washout pattern, CEH-EUS may help to differentiate pancreatic adenocarcinoma from other masses and differentiate between pancreatic neuroendocrine tumor (pNET) and inflammatory masses. The finding of a hyperenhancing lesion on CEH–EUS, both with homogeneous and inhomogeneous patterns, was a strong predictor of histology different from adenocarcinoma (94% positive predictive value). pNET was the most common hyperenhancing lesions overall. Although CEH-EUS is useful for ruling out pancreatic ductal adenocarcinoma, making the differential diagnosis between pNETs and pseudotumoral pancreatic masses is difficult because both may share an isovascular or hypervascular appearance. Currently the interpretation of CEH-EUS findings is examiner-dependent. In the future, digital image analysis by image-processing techniques should allow more objective interpretation.

Contrast-enhanced endoscopic ultrasound for pancreatobiliary disease

Endoscopic ultrasound (EUS), with or without fine needle aspiration (FNA), has become an essential tool in the evaluation of pancreatobiliary diseases. Although conventional EUS is superior to multidetector computed tomography in tumor detection and staging, there are situations when characterization of various pancreatobiliary lesions remains difficult. Contrast-enhanced EUS (CE EUS) can further improve the detection and characterization of pancreatic solid lesions such as ductal adenocarcinoma, neuroendocrine tumor, or mass-forming autoimmune pancreatitis based on differences in the enhancement pattern of the target lesions. It is also useful in differentiating between mural nodules and mucous clots in pancreatic cystic neoplasms, and characterizing various lesions in the gallbladder and bile duct. CE EUS is complementary to FNA and has the potential to increase the diagnostic yield on the first FNA needle pass.