Taller-Than-Wide Shape: A New Definition Improves the Specificity of TIRADS Systems

Abstract

Introduction: A taller-than-wide (TTW) shape is a suspicious feature of thyroid nodules commonly defined as an anteroposterior/transverse diameter (AP/T) ratio >1. An intraobserver variability of up to 18% in AP diameter evaluations has been described, which may lead to overreporting of this feature. To potentially improve the reliability of the TTW definition, we propose an arbitrary ratio of ≥1.2. Objective: The aim of this study was to estimate the impact of this definition on diagnostic performance. Methods: We prospectively analyzed 553 thyroid nodules referred for cytology evaluation at an academic center. Before fine-needle aspiration, two examiners jointly defined all sonographic features considered in risk stratification systems developed by the American Thyroid Association (ATA), the American Association of Clinical Endocrinologists (AACE), the American College of Radiology (ACR TIRADS), the European Thyroid Association (EU-TIRADS), and the Korean Society of Thyroid Radiology (K-TIRADS). TTW was defined according to the current definition (AP/T diameter ratio >1) and an arbitrary alternative definition (AP/T ratio >1.2). Results: The alternative definition classified fewer nodules as TTW (28, 5.1% vs. 94, 17%). The current and proposed definitions have a sensitivity of 26.2 and 11.9% (p = 0.03) and a specificity of 83.8 and 95.5% (p < 0.001). Thus, as a single feature, the arbitrary definition has a lower sensitivity and a higher specificity. When applied to sonographic risk stratification systems, however, the proposed definition would increase the number of avoided biopsies (up to 58.2% for ACR TIRADS) and the specificity of all systems, without negative impact on sensitivity or diagnostic odds ratio. Conclusions: Re-defining TTW nodules as those with an AP/T ratio ≥1.2 improves this marker’s specificity for malignancy. Using this definition in risk stratification systems will increase their specificity, reducing the number of suggested biopsies without significantly diminishing their overall diagnostic performance.

Diagnostic Value of Sonographic Features in Distinguishing Malignant Partially Cystic Thyroid Nodules: A Systematic Review and Meta-Analysis

“…Likewise, Kim reported that a taller than wide shape did not contribute to an increased risk of malignant PCTNs. The reason may lie in the noted inter- and even intraobserver variability of taller-than-wide shape ( 30 , 31 ). Hypoechogenicity showed fair diagnostic performance in our review (AUC = 0.8092).…”

Contemporary Thyroid Nodule Evaluation and Management

“…For these reasons, the European Thyroid Association ( 14 ), the Korean Society of Thyroid Radiology ( 15 ), and the ACR ( 32 ) have developed specific lexicons to be used with their risk-assessment systems. The definitions of certain critical nodule descriptors, such as echogenicity ( 33 ), shape ( 34 ), hyperechoic foci ( 35 ), and extrathyroidal extension ( 36 ), can significantly impact the diagnostic performance of thyroid US. As a result, interobserver agreement for US-based risk-stratification systems remains only fair to moderate (kappa, 0.34-0.44) ( 10 ).…”

Thyroid Nodule Characterization: How to Assess the Malignancy Risk. Update of the Literature

“…The TIRADS lexicon is based on internal components (solid, mixed or cystic), echogenicity (hyper-, iso-, hypoechoic or markedly hypoechoic), margins (regular, microlobulated; irregular/spiculated), the presence of calcifications (micro or macro), and shape (taller-thanwide shape is recorded when the anteroposterior diameter is greater than the transverse one [28]; wider-than-tall shape in cases where the opposite is true) at ultrasound evaluation.…”