Quantitative Shear Wave Elastography as a Prognostic Implication of Papillary Thyroid Carcinoma (PTC): Elasticity Index Can Predict Extrathyroidal Extension (ETE)

To investigate whether the quantitative elasticity index of shear wave elastography (SWE) can predict extrathyroidal extension (ETE) of papillary thyroid carcinoma (PTC) preoperatively. A total of 208 patients with pathology confirmed PTC whom underwent SWE during preoperative staging US between April 2011 to June 2012 were included.SWE indices of E (mean), E (max), E (min) of the index malignancy, the ratios between E (mean) of the lesion and parenchyma (E (ratio-P)), and muscle (E (ratio-M)), and grayscale US findings, including ETE, multifocality, bilaterality, and central and lateral lymph node (LN) metastasis were evaluated. The correlations of SWE indices and grayscale US findings with pathologic prognostic factors of PTC were analyzed by Chi square or Fisher's exact test, and multivariate regression analysis. ETE was associated with E (mean), E (max), E (min), and E (ratio-M) (P = 0.005, 0.009, 0.016 and < 0.001, respectively), multifocality was associated with E (mean), E (max), and E (min) (P = 0.028, 0.007, and 0.004, respectively), and central LN metastasis was associated with E (ratio-M) (P = 0.03). On multivariate analysis, E (mean) and E (min) were independent factors for predicting ETE (P = 0.032, 0.049, respectively). Quantitative elasticity index of SWE could predict pathologic ETE, and SWE could be a complimentary method to grayscale US for preoperative prediction of prognostic factors of PTC.