Letter to the Editor on “Two‐Dimensional Shear Wave Elastography: Utility in Differentiating Gallbladder Cancer From Chronic Cholecystitis”

Recently, Journal of Ultrasound in Medicine published an article entitled “Two-dimensional shear wave elastography: utility in differentiating gallbladder cancer from chronic cholecystitis (2023;42:1577–1585) by Soundararajan et al.”1 I read this article with great interest and commend the authors on this prospective study that compared shear wave (SW) values between gallbladder cancer (n = 46) and chronic cholecystitis (n = 51) as a screening modality before final decision making in patients with gallbladder (GB) wall thickening. The authors concluded that the mean SW value was significantly higher in gallbladder cancer patients (34 ± 17.77 kPa) than that of chronic cholecystitis patients (12.27 ± 4.13 kPa). We would like to bring forward few concerns regarding the study. First, the data regarding intra- and interobserver variability have not been provided. This becomes very important as SW values in gallbladder wall show a large instability in measurement. Recently, SW elastography has gained preferential use because of its low cost and easy manipulation of the instrument.2 Among all ultrasound (US)-based elastographies, two-dimensional (2D) SW elastography is currently the most frequently used for hepatic fibrosis quantification; this is due to its ability to sample a large area in the liver, changing the sampling area quickly under B-mode observation and displaying a color mapping of SW values over the B-mode image. The current 2DSW elastography method uses emission of multiple acoustic push-pulses to generate SWs from multiple lines in the tissue. As the SWs propagate, they cause tissue displacement, and this very minimal displacement is tracked by conventional pulse-echo US beams.3 The two-dimensional shear wave elastography (2DSWE) has been reported as useful for predicting tissue characterization. However, like conventional US beams, SWs refract and reflect at the interface between different tissues. As a result, when examining the gallbladder by 2DSWE, propagating SWs are expected to refract at the liver/gallbladder interface (Figure 1). There is another problem. Measurement of SW values is made on the assumption that the tracking US pulses propagate at regular intervals and straight from the transducer through the issue. However, these US pulses refract at the liver/gallbladder interface as well4 (Figure 2). Thus, the SWE results (especially cut-off value of 20 kPa) of the gallbladder wall must be interpreted with caution. Second, there were no cases of surgically resected gallbladder cancer in this study group. However, they authors emphasized the fact that the mean SW value of the uninvolved gallbladder regions in patients with gallbladder cancer was significantly higher than that of chronic cholecystitis, and concluded that the rest of the gallbladder wall, though it appears uninvolved on B-mode, could have microscopic infiltration or metaplastic tissue. We cannot agree with this opinion, because we must consider many other possibilities, including severe fibrosis, or degeneration, and others (all these factors are expected to increase SW values). Third, all their chronic cholecystitis cases were probably complicated by acute change (for this, symptomatic), thus did not reflect a wide spectrum of chronic cholecystitis (eg, xanthogranulomatous cholecystitis). We hope you find our feedback to be useful and we are interested to hear about the authors' opinion regarding our questions. However, the authors should be congratulated, since many of these suggestions give us important hints about how we perform 2DSWE for patients with gallbladder disease.