Contrast Enhanced Endoscopic Ultrasound Imaging for Gastrointestinal Subepithelial Tumors

Abstract

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 hyperenhancement pattern in gastrointestinal stromal tumors (sensitivity, 78%-100%; specificity, 60%-100%; accuracy, 60%-100%) and hypoenhancement 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 contrastenhanced ultrasound. However, there will be subjective-bias and the results depends on the performer's skill.

Keywords: Contrast-enhanced endoscopic ultrasound; Gastrointestinal stromal tumor; High; Subepithelial tumor.

Fig. 1.

Basis of contrast harmonic imaging. Upon exposure to ultrasound beams, microbubbles in the contrast agent oscillate, resulting in resonation and release of many harmonic signals. Upon receiving the transmitted ultrasound waves, tissues and microbubbles both produce harmonic components from the microbubbles. The harmonic components from microbubbles are at a higher level than those from the tissue. By selectively depicting the second harmonic component, signals from microbubbles are visualized more strongly than those from the tissue.

Fig. 2.

Contrast-enhanced harmonic endoscopic ultrasound (CH-EUS) images of gastrointestinal stromal tumor (GIST). (A, B) CH-EUS image of a GIST. (A) Fundamental B-mode EUS shows a low echoic tumor. (B) An image of CH-EUS demonstrating the hyper-enhancement pattern. (C, D) CH-EUS image of a leiomyoma (C) B-mode EUS shows a low echoic tumor. (D) An image of CH-EUS demonstrating the hypo-enhancement pattern.

Fig. 3.

Contrast-enhanced harmonic ultrasound (CH-US) images of gastrointestinal stromal tumor (GIST). (A, B) GIST with “poor” pattern on abdominal ultrasound and contrast-enhanced harmonic abdominal ultrasound. (A) Fundamental B-mode abdominal ultrasound shows iso-echoic tumor. (B) An image of CH-US showing blood flow restricted to the periphery, without filling the parenchymal flow of the tumor (C, D). GIST with “rich” pattern on abdominal ultrasound and contrast-enhanced harmonic abdominal ultrasound. (C) Fundamental B-mode abdominal ultrasound showing an iso-echoic tumor. (D) An image of CH-US shows plentiful vessels extending from the periphery to the tumor center.

Fig. 4.

Detection of intratumoral vessels in gastrointestinal stromal tumor by contrast-enhanced harmonic endoscopic ultrasound (CH-EUS). (A) Fundamental B-mode EUS shows a low echoic mass. (B) A vessel image of CH-EUS demonstrating irregular vessel subepithelial intratumoral vessels (arrow heads) originating peripherally and extending centrally into the tumor.

Fig. 5.

Detection of heterogeneous enhancement in gastrointestinal stromal tumor by contrast-enhanced harmonic endoscopic ultrasound (CH-EUS). (A) Fundamental B-mode EUS shows a low echoic mass. (B) A perfusion image of CH-EUS demonstrating the heterogeneous enhancement.

Fig. 6.

Detection of non-enhancing spots in gastrointestinal stromal tumor by contrast-enhanced harmonic endoscopic ultrasound (CH-EUS). (A) Fundamental B-mode EUS shows a low echoic mass. (B) A perfusion image of CH-EUS demonstrating the non-enhancing spot.