The role of qualitative elastography in thyroid nodule evaluation: exploring its target populations.

Abstract

Thyroid nodules are frequently found and pose a dilemma to the clinician, as only a few harbor a malignancy, and the majority of nodules are benign. The standard work-up of thyroid nodules consists of ultrasound and fine needle aspiration (FNA), both having their limitations [1, 2]. In particular, ultrasound lacks criteria for determining whether a nodule is malignant [3]. FNA shows good sensitivities and specificities, but inconclusive and indeterminate results are frequently found, resulting in the need for a diagnostic thyroid lobectomy to obtain a final diagnosis [4]. In the long lasting search to reduce the number of invasive diagnostic procedures, real-time qualitative elastography has been proposed to fulfill this need. Elastography determines the elasticity of the thyroid nodule. Soft nodules are assumed to be benign, whereas hard nodules are considered to be malignant. Qualitative elastography represents the elasticity of the nodule in a colored image projected over the ultrasound image. Multiple elasticity scoring systems are used, which makes reviewing literature challenging. Most common is the 4-point scale developed by Asteria et al., in which elastography 1 (ES 1) is assigned to nodules with elasticity in the entire nodule, ES 2 is assigned to nodules with elasticity in a large portion of the nodule, ES 3 is assigned to nodules with stiffness in a large portion of the nodule, and ES 4 is assigned to hard nodules. A cut-off between ES 2 and ES 3 is widely accepted to discriminate benign from malignant nodules [5]. Studies on thyroid nodule elastography have focused on different target populations: (1) patients referred for FNA with the aim to reduce the number of FNAs, and (2) patients with an indeterminate FNA result (i.e., Bethesda classification III or IV), with the aim to reduce the number of futile lobectomies. Recently, we performed a meta-analysis of studies that investigated the first population: patients referred for FNA. The aim of this study was to determine whether elastography could determine the nature of thyroid nodules and thereby identify those that require further analysis by FNA [6]. In this study, analyzing twenty reports including 3908 nodules, two different cut-offs were examined. The first was the standard cut-off between ES 2 and 3. The second used a cut-off between ES 1 and 2, meaning that only the completely soft nodules were considered benign and the rest of the nodules as potentially malignant. Both cut-offs showed that elastography is an excellent tool to diagnose benignity, with a respective negative predictive value (NPV) of 97 and 99 %. Based on these outcomes, it was concluded that in these cases FNA could be omitted safely. However, considering the modest positive predictive value (PPV) of only 40 % of elastography, this implies that any nodule with an elastography score above ES 2 requires further analysis [6]. In the current issue of Endocrine, Trimboli et al. published an extensive review and meta-analysis on nodules with an indeterminate FNA [7]. Although the majority of these nodules are benign, around one in four harbors a malignancy [4]. Diagnostic lobectomies are often Jakob W. Kist and Sjoerd Nell have contributed equally to the manuscript.