The role of superb microvascular imaging and shear wave elastography in differatiation of intrathyroidal ectopic thymus tissue and thyroid nodule in children

OBJECTİVE :In children, sonographic examination of the thyroid gland suggests that the intrathyroidal ectopic thymus tissue may interfere with papillary thyroid cancer due to punctate internal echogenicity. In this study, we planned to obtain quantitative data using superb microvascular imaging (SMI) and shear wave elastography mode. It would be possible to recognize and differantiate intrathyroidal ectopic thymus tissue from thyroid nodule in order to prevent unnecessary biopsies by quantitative evaluation. MATERIAL AND METHOD: Twenty-seven thyroid nodules (mean age: 15.6 years) and 20 intrathyroidal ectopic thymus (IET) (mean age: 8.8years) tissues were evaluated in 47 patients. Vascularity index via SMI and elasticity (kPa and m/sn) and velocity via SWE hava been evaluated in both group. The age, vascularity indicis and elasticity parameters were expressed in terms of minimum, maximum, mean and standard deviation.Correlation between volume, elasticity and vascularity index of the lesions and diagnostic accuracy via ROC analysis were studied. RESULTS: Median vascularity index of the IET is 4.7% (range 0,2-16%) while that is 23,8%(7,5-40) in the nodules. Median elasticity values were 7.6kPa (4.4-9.5kPa) in IET while those were 15.58kPa (8.5-23.4kPa) in the nodules respectively. Significant positive correlation was found between vascularity index and volume (p:0.018), vascularity index and elasticity (p:0.001), elasticity and volume (p: 0.001) values. There was also a significant positive correlation between the age and the volume of the lesions. When the cut off value was set to13% in VI the the sensitivity , specificity, positive and negative predictive values were in differerntiating nodules were 88%,95%,95%,86% respectively. When the cut off value of the elasticity was set to 9.2 kPa; the sensitivity , specificity, positive and negative predictive values were 92%,95%,96%,90% in differerntiating nodules respectively. CONCLUSION : In children, intrathyroidal ectopic thymus tissue should be considered in the differential diagnosis of thyroid nodule. In our study, increased vascularity index and high elasticity and velocity values were found on SMI and shear wave elastography of thyroid nodules compared to IET. All these values obtained, confirmed that SMI and SWE have high consistency of differentiation between these two antities and can be used to improve the diagnostic accuracy. By using these two advanced ultrasound methods in the differential diagnosis, unnecessary surgery and interventional procedures will be avoided. Key Words: SMI, Shear Wave Elastography, İntrathyroidal ectopic thymus,Thyroid nodule