The role of us-elastography in the differential diagnosis of nodules associated with chronic thyroiditis

The aim of this study was to evaluate diagnostic performance of US-elastography in differentiating benign and malignant thyroid nodules with chronic thyroiditis, to compare with grey scale US and Doppler findings.Patients with chronic thyroiditis who had a coexisting nodule that was proven by fine needle aspiration or surgical pathologic analysis to be benign (n=67) or malignant (n=7). Thus, 69 patients with 74 nodules were included in the study. Their ages were between 18-78 years and the mean age was 49. Sixty four of them were female and 5 of them were male. All patients were evaluated with B-mode, color Doppler US and elastography by using Hitachi EUB 7500 digital ultrasound equipment. All images were recorded digitally. A careful evaluation of the following US parameters was performed on all thyroid nodules: internal structure (solid/mixed solid-cystic), echogenity, presence or absence of hypoechoic halo sign, microcalcifications, `taller than wide? sign, number and size. Color or Power Doppler or both were used to evaluate whether the nodule is avascular or vascular. The distribution of the flow was also assessed (reguler or irregular course of vascular structures).Patients were divided into two groups to determine the typical sonographic appearance of nodular thyroiditis; including nodules with (67/74) and without (7/74) sonographic evidence of backround diffuse thyroiditis. There was no statistically significant difference in grey scale and Doppler findings between two groups. Nodules in chronic lymphocytic thyroiditis were more likely to be solid (53/74) and hypoechoic (43/74).The US elastographic image was matched with an elasticity color scale and nodules were classified into 4 groups using elasticity score. All images were assessed by two radiologists who were blinded to the patient?s final diagnosis. Decisions regarding the findings were reached by consensus. In addition, parenchyma-to-tumor strain ratio (strain index) was calculated. Strain ratio of all nodules was measured two times and mean strain ratio values were calculated for all nodules. Grey scale properties, vascularity scores, elasticity scores and mean strain ratios of all nodules were compared with their pathologic diagnosis.Sixty seven of all nodules were benign and seven were malignant. Five of all malignant nodules were papillary carcinoma, one of them was lymphoma and one of them was thyroid carcinoma including different differentiation areas (papillary carcinoma+epidermoid carcinoma+ sarcomatous component). Sex, number of nodules, size of nodule and inner structure were not statistically related with malignancy. Hypoechogenicity, absence of halo, microcalcifications, blurred margin, `taller than wide? sign and irregular course of vascular structures were statistically related with malignanc.There was a statistically significant relation between high elasticity score and malignancy (p<0,001). The sensitivity of Score 4 elasticity was 71,4%, specificity was 95,5% positive predictive value was 62,5%, negative predictive value was 97% and accuracy was 93,2%.We determined 6,16 as the cut-off point of the strain ratio. There was a statistically significant difference between the nodules with the strain ratio above and below 6,16 (p<0,001). The sensitivity of the strain ratio above 6,16 was 71,4%, the specificity was 100%, positive predictive value was 100%, negative predictive value was 97,1%, accuracy was 97,3 %.Solid internal structure, hypoechogenity, absence of hypoechoic halo sign and irregular course of vascular structures in nodule had the highest sensitiviy (100%); the strain ratio above 6,16 had the highest specificity (100%) among all nodule characteristics.US-elastography is an assisting imaging technique to differentiate benign and malignant nodules associated with chronic thyroiditis.