Elastography Methods in the Prediction of Malignancy in Thyroid Nodules

*Andreea Borlea, Laura Cotoi, Corina Paul, Felix Bende and Dana Stoian*

#### **Abstract**

Ultrasonography provides a primary stratification of the malignancy risk of thyroid nodules for selecting those that need further evaluation by fine-needle aspiration cytology (FNAC). Ultrasound elastography (USE) methods have been more recently proposed as a promising tool, aiming to increase the accuracy of baseline ultrasound. By means of USE, stiffness is assessed as an indicator of malignancy. Strain elastography was the first method used in thyroid imaging, with very good accuracy in discerning thyroid cancer. More recently, 2D shear-wave elastography also confirmed to be a valuable tool with similar outcomes. The advantages, limitations, and technical details of the elastography methods currently used in assessing thyroid morphology, particularly thyroid nodules, will be presented and compared in this chapter.

**Keywords:** thyroid imaging, elastography, strain, shear wave, malignancy risk

#### **1. Introduction**

Thyroid nodules are among the most common thyroid pathologies, and their etiology is diverse [1, 2]. They represent masses of abnormal proliferation, formation, and structure within the thyroid parenchyma [3]. The prevalence of thyroid nodules increases with age, reaching up to 50% after 65 years, and they are more commonly found in women [4]. The diagnosis of nodules less than 1 cm, as well as lesions with a deep location, is most commonly missed at physical examination; thus, thyroid imaging techniques have drawn increasing clinical attention [5]. Conventional neck ultrasound (US) is still the preferred method for assessing thyroid morphology, including the presence and appearance of thyroid nodules [6–9].

Thyroid cancer accounts for the most common endocrine malignancy, with a slowly increasing incidence [10, 11]. Its prevalence reaches 7–15% in the group of thyroid nodules [12], and it does remain one of the cancers with the least risk of death [13]. There are certain categories considered at greater risk for cancer, such as young adults, children, and patients with a history of neck irradiation [14]. Size also seems to impact the prevalence of malignancy; nodules larger than 2 cm were more often

malignant compared to smaller lesions [15], but multinodular goiters do not seem to increase the likelihood of malignancy [16].

Fine-needle aspiration cytology (FNAC) represents the procedure of choice for further examining the thyroid lesions with high-risk features documented by means of clinical or US evaluation [17]. Thyroid cytology is most commonly reported using the Bethesda classification (I-VI), with different prediction of malignancy for each category, which is meant to guide the case management decision [18]. A less aggressive approach to diagnosis and treatment was introduced starting with the 2015 American Thyroid Association (ATA) guidelines, which advise reducing FNAC indications and endorse "active surveillance" of tumors with very low risk [19].

Ultrasound elastography (USE) proved to be a valuable imaging tool in predicting the risk of malignancy of thyroid nodules [20, 21] and also in decreasing the FNAC indication [17, 22]. It assesses tissue distortion in reply to stress, assuming that a hard lesion presents an increased likelihood of cancer.
