Letter to the Editor on “Shear Wave Elastography in the Diagnosis of Tumor Extent of Basal Cell Carcinomas”

Abstract

Dear EditorBasal cell carcinoma (BCC) is the most common cutaneous tumor, mostly involving the head and neck. 1 It is absolutely necessary to preserve as much surrounding normal skin as possible as well as remove the tumor without leaving tumor tissue. Generally speaking, surgical tumor resection is performed by determining the resection margin 4-10 mm outwards based on visual observation boundaries (VOB), because it is extremely challenging to determine accurately the tumor extent before histological examination. High-frequency ultrasound (HFUS) is thought to be the ideal diagnostic tool for evaluating the tumor extent.A large number of case reports and articles have been published in order to share knowledge and experiences in this field. Recently, Journal of Ultrasound in Medicine published an article entitled "Usefulness of shear wave elastography in determining the tumor extent of basal cell carcinomas (2023;42:971-976)" 2 in which the authors concluded that shear wave elastography (SWE) was helpful in determining the tumor extent of BCC. We commend the authors for providing such a meticulous data of cutaneous US. In their study, SWE parameters (E av and E sd ) were measured 1-mm intervals in four clock directions, and then the E ratio of region of interest (ROI) at a distance of 1, 2, 3, and 4 mm was calculated. The authors should be congratulated, since many of these suggestions are widely shareable. However, we think some results should be interpreted very cautiously; 1) the E ratio between real tumor boundaries and optimal surgical margins was statically significant, shown by their SW value measurements. However, this SW measurement is problematic. Current SWE measures SW propagation velocity based on the assumption that the medium has a homogeneous structure, uniform density, and purely elastic. 3 In reality, however, like conventional US beams, SWs refract at the tumor-surrounding tissue boundary according to Snell's law, and the abovementioned measurement of SW values under SWE image is largely compromised by US refraction. Additionally, SWs reflect at the boundary. Thus, a discrete attitude is always necessary when evaluating tumor boundaries by SWE (Figure 1). This idea is certainly very discouraging for SWE in clinical practice to diagnose cutaneous tumors. Nevertheless, we propose that 2DSWE may be useful for observing intratumor heterogeneity. 2) There was no comparison between B-mode US and SWE in terms of tumor boundary