US-Elastography in Differential Diagnosis of Benign and Malignant Thyroid Nodules

Abstract

Thyroid nodules are increasingly detected during thyroid evaluations or incidentally during ultrasound examinations for other clinical purposes or screening programs, leading to potential overdiagnosis and overtreatment; thus, the present thyroid nodules' epidemic represents a challenge for the clinical management, since the vast majority of discovered nodules end up being diagnosed as benign. Thyroid Imaging Reporting and Data System (TI-RADS) was proposed to facilitate understanding and communication of US reports among specialists. Furthermore, technology developments including CEUS and US-elastography have opened further prospects of ultrasound leading to the possibility to perform the advocated multiparametric ultrasound. Assessing stiffness as indicator of malignancy, using either SE (strain quasistatic elastography) or SWE (Shear wave elastography), is recognized as a valid and useful additional tool to gray-scale and color Doppler US in thyroid evaluation. It may be performed with no patient preparationand dedicated equipment that supports elastography is required. Elastography is especially recommended as an additional tool to conventional ultrasound and to guide follow-up of lesions previously diagnosed as benign at FNA biopsy and can be used in combination with conventional US to improve specificity. To date the majority of papers and the meta-analyses present in literature showed US-elastography more accurate than Ultrasound with a few exceptions. However, what was clearly debated and reported is that to achieve reliable SE, adequate training, suitable cut-off values for both strain and SWE, adequate equipment and clinically appropriate examinations are necessary. Expert suggestions are to minimize pre-compression, carotid pulsation artefacts, to check the ROI size and positions, avoid areas with artifacts or with gross calcifications or cystic areas and instruct patients to cooperate properly. There are still open and debated issues such as which is the most accurate and reproducible elastographic techniques; which is the role of U-elastography for thyroid nodules indeterminate at FNAC; which is the reproducibility of these techniques and how much thyroiditis may influence the US-elastography accuracy in thyroid nodules characterization. Limitations and perspectives will be presented.