Shear Wave Elastography in Evaluation of Cervical Lymph Node Metastasis of Papillary Thyroid Carcinoma: Elasticity Index as a Prognostic Implication

The aim of this study was to evaluate the usefulness of shear wave elastography (SWE) for predicting cervical lymph node (LN) metastasis and the prognostic implication of SWE as histopathologic factors of papillary thyroid carcinoma (PTC). Eighty-four LNs of 66 patients with PTC underwent B-mode ultrasonography (BUS) and SWE before ultrasound-guided fine-needle aspiration biopsy or preoperative evaluation. SWE elasticity indices (EI) of mean (E-mean), minimum (E-min), maximum (E-max) and the ratio of E-mean in LNs and surrounding muscle (Emean-m) were measured at the stiffest portion of LNs (kPa). SWE EI were correlated with the pathologic diagnosis and the histopathologic findings, including number and size of metastatic LNs, the ratio of the number of metastatic LN/dissected LN, and the presence of extranodal extension. Diagnostic performances of SWE EI and BUS for predicting LN metastasis were assessed using receiver operating curve analysis. All SWE EI were significantly higher in metastatic LNs than in benign LNs (p < 0.005). Combined E-mean [area under the curve (AUC) 0.811] or E-min (AUC 0.812) with BUS showed significantly higher AUC than BUS (0.738) for predicting metastatic LNs (p = 0.041 and 0.033, respectively). The number of positive LNs/dissected LNs and the largest LN size were significantly correlated with SWE EI (p < 0.05 and p < 0.005, respectively). Metastatic LNs with extranodal extension showed significantly higher SWE EI (p < 0.005) than those without extranodal extension. Combined use of SWE and BUS was adjunctive to the diagnostic performance of BUS for the prediction of LN metastasis of PTC, and quantitative SWE could predict pathologic prognostic factors of LN metastasis of PTC.