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Current practice and new insights in thyroid ultrasound

Author:

Emmanuel Coche

Department of radiology, Cliniques Universitaires Saint-luc, Université Catholique de Louvain, Brussels, BE
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Abstract

Thyroid nodules are common and detected in 2–6% in the adult population by palpation. This prevalence increased to 40–60% with the use of ultrasound. Thyroid cancer is rare, with 1020 new cancers (751 women and 287 male) registered in 2019 in Belgium [1]. Ultrasound imaging represents the cornerstone for the thyroid nodule work-up and has benefited from significant improvements in recent years. We succinctly focus on how to evaluate thyroid nodules using ultrasonography and how to use the European Thyroid Imaging and Reporting Data System (EU-TIRADS score). We will also review the possible added value of complementary ultrasound techniques such as high-resolution colour Doppler ultrasound and elastography. Further, we discuss how to select at-risk nodules to benefit from fine-needle aspiration cytology and finally we briefly review new techniques for the treatment of thyroid nodules and the role of artificial intelligence in thyroid nodule classification.

How to Cite: Coche E. Current practice and new insights in thyroid ultrasound. Journal of the Belgian Society of Radiology. 2022;106(1):115. DOI: http://doi.org/10.5334/jbsr.2950
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  Published on 18 Nov 2022
 Accepted on 29 Sep 2022            Submitted on 26 Sep 2022

Categorization of Thyroid Nodules Using EU-TIRADS

Various risk stratification systems exist to categorize the risk of malignancy based on the ultrasound appearance of a thyroid nodule. The EU-TIRADS issued by the European Thyroid association in 2017 was the last to have been published [2]. This system categorizes nodules into five categories ranging from 1 – normal appearances to 5 – malignant on US criteria as illustrated in Table 1 and Figure 1.

Table 1

The EU-TIRADS score according to reference 2.


CATEGORY US FEATURES MALIGNANCY RISK, %

EU-TIRADS 1: normal No nodules None

EU-TIRADS 2: benign Pure cyst
Entirely spongiform
≅0

EU-TIRADS 3: low risk Ovoid, smooth isoechoic/hyperechoic
No features of high suspicion
2–4

EU-TIRADS 4: intermediate risk Ovoid, smooth, mildly hypoechoic
No features of high suspicion
6–17

EU-TIRADS 5: high risk At least 1 of the following features of high suspicion:
– Irregular shape
– Irregular margins
– Microcalcifications
– Marked hypoechogenicity (and solid)
26–87

Fine needle aspiration revealed thyroid cancer in this EU-TIRADS V nodule
Figure 1 

An 18-year-old woman presented at the ultrasound unit for a thyroid nodule discovered incidentally at the school medical examination. No familial risk factor was noted. Blood sample revealed a normal TSH level and no thyroglobulin raise. Ultrasound was performed (Figure 1A) and revealed a 1.5 cm thyroid nodule containing many hyperechoci foci suggestive of microcalcifications. The nodule was classified as EU-TIRADS V.

According to the European guidelines, a fine-needle aspiration (FNA) cytology under ultrasound guidance was therefore performed and revealed abnormal cells consistent with a thyroid carcinoma (Bethesda 6) (Figure 1B).

Colour Doppler Ultrasound

The use of colour Doppler and power Doppler imaging for characterisation of thyroid nodule vascularity is widely used currently. It is considered a nonspecific feature for malignancy even if the presence of intranodular flow raises more concerns than if there is no flow or just perinodular flow is seen. A new Doppler technique was recently developed that improved microvascular flow imaging (Figure 2). Its diagnostic capacities to better detect malignancy in thyroid nodules has to be demonstrated in large and unselected population [3].

Microvascular imaging depicts better the intranodular vascularity
Figure 2 

Comparison between vascularity obtained by colour Doppler imaging (Figure 2A) and a new technique depicting the microvascular flow imaging (Figure 2B).

Elastography in Thyroid Nodules

The primary application of elastography is the differential diagnosis of thyroid cancer. Nevertheless, despite the increasing data coming from the literature, a univocal consensus on its role in the selection of thyroid nodules to biopsy is still lacking [4].

FNA or Core Biopsy?

Nodules are selected for fine-needle aspiration biopsy on the basis of ultrasound features, size, and high-risk clinical history. Cytology results are classified by the Bethesda system into six categories ranging from benign to malignant. Limitations of FNA include a substantial rate of inconclusive results or indeterminate interpretations (2–30%). When cytology is indeterminate, molecular testing can further risk-stratify patients for observation or surgery. Core-needle biopsy (CNB) has been suggested as a complementary or even alternate method to FNA with a greater diagnostic accuracy compared to repeated FNA but sill with some limitations regarding differentiation between follicullar neoplasms and hyperplastic nodules [5].

Ultrasound-Guided Ablation Procedures for Thyroid Nodules

There is an increasing interest to use ultrasound-guided thermal ablation procedures to treat both benign and malignant thyroid nodules. Thermal ablation techniques are differentiated based on the method used to develop this temperature differential and include radiofrequency ablation (RFA), laser ablation, microwave ablation and high-intensity focused ultrasound. For benign thyroid nodules, RFA appears the most effective US-guided ablation technique for treating solid, mixed, and spongiform nonfunctioning thyroid nodules. RFA is a developing application in primary thyroid cancer with some efficacy in the setting of recurrent and residual thyroid malignancy. Standardization of practices and reporting has emerged as an important component of multidisciplinary application of these technologies [6].

Artificial Intelligence (AI) and Thyroid Nodules

There is evidence that AI increases diagnostic accuracy and significantly limits inter-observer variability by using standardized mathematical algorithms. It could also be of aid in practice settings with limited sub-specialty expertise, offering a second opinion by means of radiomics and computer-assisted diagnosis. However, the real effectiveness of AI systems remains controversial, taking into consideration the largest and most scientifically valid studies [7].

Competing Interests

The author has no competing interests to declare.

References

  1. Cancer Burden in Belgium 2004–2017, Brussels: Belgian Cancer Registry; 2020. 

  2. Russ G, Bonnema SJ, Erdogan MF, Durante C, NGU R, Leenhardt L. European Thyroid Association Guidelines for Ultrasound Malignancy Risk Stratification of Thyroid Nodules in Adults: The EU-TIRADS. Eur Thyroid J. 2017; 6(5): 225–237. DOI: https://doi.org/10.1159/000478927 

  3. Capelli C, Pirola I, Gandossi E, et al. Ultrasound microvascular blood flow evaluation: A new tool for the management of thyroid nodule? Int J Endocrinol. 2019; 7874890. eCollection 2019. DOI: https://doi.org/10.1155/2019/7874890 

  4. Kwak JY, Kim E-K. Ultrasound elastography for thyroid nodules: Recent advances. Ultrasonography. 2014; 33: 75–82. DOI: https://doi.org/10.14366/usg.13025 

  5. Pantanowitz L, Thompson LDR, Jing X, Rossi ED. Is thyroid core needle biopsy a valid compliment to fine needle aspiration? J Am Soc Cytopathol. 2020; 9(5): 383–388. DOI: https://doi.org/10.1016/j.jasc.2020.06.003 

  6. Orloff LA, Noël JE, Stack, BC, Jr., Russel MD, et al. Radiofrequency ablation and related ultrasound-guided ablation technologies for treatment of benign and malignant thyroid disease: An international multidisciplinary consensus statement of the American Head and Neck Society Endocrine Surgery Section with the Asia Pacific Society of Thyroid Surgery, Associazione Medici Endocrinologi, British Association of Endocrine and Thyroid Surgeons, European Thyroid Association, Italian Society of Endocrine Surgery Units, Korean Society of Thyroid Radiology, Latin American Thyroid Society, and Thyroid Nodules Therapies Association. Head Neck. 2022; 44(3): 633–660. DOI: https://doi.org/10.1002/hed.26960 

  7. Sorrenti S, Dolcetti V, Radzina M, et al. Artficial intelligence for thyroid nodule characterization: Where are we standing? Cancers (Basel). 2022; 14(14): 3357. DOI: https://doi.org/10.3390/cancers14143357 

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