Reappraisal of shear wave elastography as a diagnostic tool for identifying thyroid carcinoma

Abstract

Thyroid nodular disease is common, but predicting the risk of malignancy can be difficult. In this prospective study, we aimed to assess the diagnostic accuracy of shear wave elastography (SWE) in predicting thyroid malignancy. Patients with thyroid nodules were enrolled from a surgical tertiary unit. Elasticity index (EI) measured by SWE was registered for seven EI outcomes assessing nodular stiffness and heterogeneity. The diagnosis was determined histologically. In total, 329 patients (mean age: 55 ± 13 years) with 413 thyroid nodules (mean size: 32 ± 13 mm, 88 malignant) were enrolled. Values of SWE region of interest (ROI) for malignant and benign nodules were highly overlapping (ranges for SWE-ROImean: malignant 3-100 kPa; benign 4-182 kPa), and no difference between malignant and benign nodules was found for any other EI outcome investigated (P = 0.13-0.96). There was no association between EI and the histological diagnosis by receiver operating characteristics analysis (area under the curve: 0.51-0.56). Consequently, defining a cut-off point of EI for the prediction of malignancy was not clinically meaningful. Testing our data on previously proposed cut-off points revealed a low accuracy of SWE (56-80%). By regression analysis, factors affecting EI included nodule size >30 mm, heterogeneous echogenicity, micro- or macrocalcifications and solitary nodule. In conclusion, EI, measured by SWE, showed huge overlap between malignant and benign nodules, and low diagnostic accuracy in the prediction of thyroid malignancy. Our study supports that firmness of thyroid nodules, as assessed by SWE, should not be a key feature in the evaluation of such lesions.

Keywords: diagnosis; elastography; thyroid; ultrasonography.

Figures

Figure 1

SWE image depicting the ROIs used for EI measurements. Color-coded elasticity map overlying the B-mode US image. Soft areas with a low EI are colored blue, and changes to green, yellow and red with higher EI and increasing stiffness. To the right, the elasticity scale (0–100 kPa, top) and the EI measurements for the predefined ROIs (bottom) are shown.

Figure 2

Flow of patients. *Including seven patients with thyroid micro-carcinoma.

Figure 3

Plot for SWE-ROImean specified by histological diagnosis. Box-and-whisker plot: The boxes display the interquartile range (IQR) and the median, while the whiskers display 1.5 times the IQR. Outliers beyond the whiskers are marked with individual dots. Elasticity index (EI); kilo Pascal (kPa); benign, n = 325; papillary thyroid carcinoma (PTC), n = 57; follicular thyroid carcinoma (FTC), n = 16; medullary thyroid carcinoma (MTC), n = 1; thyroid micro-carcinoma (miTC), n = 9. Other: lymphoma (n = 1), renal cell carcinoma metastasis (n = 2), myxofibrosarcoma (n = 2 in one patient). The one outlier in the benign group is not shown (EI = 182 kPa).