Temporal Trends in Thyroid Nodule Size on Ultrasonography

Key Points

Question

How has reported thyroid nodule size changed over time?

Findings

In this systematic review and meta-analysis of 28 studies and 11 963 patients, reported thyroid nodule size increased during the last 30 years in diagnostic ultrasonography studies while reported nodule size decreased in screened populations.

Meaning

The study results suggest that the size of thyroid nodules reported on thyroid ultrasonography has increased over time concomitant with changing nodule risk stratification systems and guidelines that have been designed to improve diagnostic yield and reduce overdetection of subclinical disease.

Abstract

Importance

In recent years, concern has grown around the overdetection of thyroid cancer. Changes to thyroid nodule risk stratification systems and guidelines were made to improve diagnostic yield. It is not known how these advancements have affected the size of thyroid nodules reported on ultrasonography over time.

Objective

To evaluate change in reported nodule size since 1990, particularly between studies of thyroid ultrasonography obtained for diagnostic vs screening purposes.

Study Selection

The systematic review included original research studies that reported thyroid nodule size in adults undergoing their first thyroid ultrasonography. Excluded studies were those that included patients with known thyroid disease, prior thyroid ultrasonography, nodules identified through other imaging modalities, and/or that had constraints on nodule size and/or characteristics.

Data Sources

PubMed, SCOPUS, CENTRAL, and CINAHL were reviewed from January 1990 to March 2021. Study characteristics, patient demographic characteristics, nodule size, and ultrasonography techniques were independently extracted by multiple observers.

Main Outcomes and Measures

The size of thyroid nodules reported via ultrasonography over time. Mixed-effects meta-regression models were used to evaluate mean nodule size (1) overall, (2) in studies that used ultrasonography diagnostically, and (3) in studies that used ultrasonography for screening.

Results

A total of 11 963 patients were included; the mean (SD) age was 47.6 (5.2) years. A total of 1097 studies were identified; of these, 395 full-text articles were assessed, and 18 studies met inclusion criteria. All were done at academic institutions. Altogether, these studies had 11 963 patients who underwent a first thyroid ultrasonography. Reported mean nodule size increased 0.52 mm each year from 1990 to 2021 (95% CI, 0.2-0.81). Diagnostic subgroup mean nodule size increased 0.57 mm each year from 1990 to 2021 (95% CI, 0.21-0.93). Screening subgroup mean nodule size decreased by 0.23 mm each year up to 2012 (95% CI, −0.40 to −0.07).

Conclusions

The results of this systematic review and meta-analysis suggest that thyroid nodule size reported on diagnostic ultrasonography has increased over time in conjunction with changes in risk stratification systems, nodule guidelines, and radiology practice patterns. Conversely, a decrease in size reported in asymptomatic, ultrasonography-screened populations was observed. Findings from screening studies show that subcentimeter nodules are prevalent and easily identified with ultrasonography, but clinical relevance is questionable. Altogether, these results may provide insight into how ultrasonography guidelines and practice patterns have changed thyroid nodule reporting over time and can inform future guidelines and policies associated with thyroid nodule management.

This systematic review and meta-analysis examines changes in reported nodule size since 1990, particularly between studies of thyroid ultrasonography obtained for diagnostic vs screening purposes.

Introduction

Diagnostic ultrasonography technology, introduced in the 1960s, has remained the standard of care for anatomic thyroid examination since the early 1990s.^1,2 Ultrasonography is low risk, efficient, and widely accessible; as such, medical specialists from several disciplines regularly use it to examine the thyroid for nodules.^3,4 Interpretation guidelines and risk stratification systems have improved the diagnostic yield, with concerning or suspicious nodules now rated and reported in a more standard fashion. Features suspicious for cancer (eg, microcalcifications, irregular margins in combination with size criteria) are specifically identified to guide the utility and necessity of further workup.^2,5,6

The use of high-resolution ultrasonography improves the ability to precisely evaluate nodule (1) size, (2) location, and (3) sonographic features (eg, composition, echogenicity, margins, orientation, calcifications, vascularity, and extrathyroidal extension).^4,7,8 Enhanced-resolution ultrasonography also allows for detection of smaller nodules.⁸ The standard recommended and reported frequency for thyroid ultrasonography of 10 MHz allows for routine detection of nodules measuring less than 0.5 cm.⁹ Identification of small, nonpalpable, and likely nonpathologic thyroid nodules creates a disease paradigm that must balance incidental findings, risk-benefit analysis, health care costs, and access to care when deciding how to work up and treat these patients.

Introduction of nodule risk stratification systems (eg, American College of Radiology Thyroid Imaging Reporting and Data System [ACR TI-RADS⁷]) and guidelines (eg, American Thyroid Association [ATA]⁴) is increasingly important as ultrasonography technology has become more ubiquitous and advanced. These systems and guidelines intend to mitigate growing concerns of overdetection and overtreatment of small thyroid nodules and subclinical disease. Most guidelines do not recommend biopsy of nodules less than 1 cm unless concerning features are present.^4,8,10,11 However, radiologists may still report subcentimeter nodules, as they are well-visualized on ultrasonography studies. These reports, particularly to patients or practitioners unfamiliar with guidelines, can cause concern or even prompt additional workup. To our knowledge, there is little existing evidence describing the trend in the size of reported thyroid nodules on ultrasonography during the time that these guidelines, risk stratification systems, and subsequent change in practice patterns occurred. The purpose of this systematic review and meta-analysis was to determine how the reported size of thyroid nodules has changed over time. We hypothesized that reported nodule size has decreased over time due to a combination of better ultrasonography technology and the increased ubiquity of ultrasonography in clinical practice. However, it is also possible that improved guideline adherence has been associated with increased reported nodule size. Characterizing changes in nodule size reported over time may help to inform clinical practice, decision-making, and future guidelines associated with thyroid nodule workup.¹²

Methods

Data Source

The systematic review protocol was registered in PROSPERO (CRD42021253731). PubMed, SCOPUS, Cochrane Central Register of Controlled Trials (CENTRAL), and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases were searched for peer-reviewed original research articles that reported thyroid nodule sizes identified on ultrasonography that were published from January 1990 to March 2021. A research librarian (M.H.) assisted with all searches.

Study Selection

Physicians and researchers with expertise in thyroid nodules and ultrasonography developed inclusion and exclusion criteria (D.O.F., L.M.G., S.F.T., and N.A.). Included studies were originally published in English, were peer-reviewed articles with at least 20 adults (age ≥18 years), and included only patients who were undergoing their first thyroid ultrasonography. Studies reporting the size (mm) of a single identified nodule or only the largest nodule, if multiple were present, were included in the meta-analysis. To minimize the risk of interpretation bias, we excluded studies that included patients with a history of thyroid disease or nodules and/or nodules identified through other imaging modalities (eg, computed tomography, magnetic resonance imaging, nuclear medicine scan). We also excluded any study that only analyzed nodules that met certain size or characteristic constraints to ensure that the sample was representative of all nodules and did not skew nodule size larger or smaller. Two investigators (among Y.Z., V.H., C.J., E.M., and A.A.) independently screened each abstract and subsequent full-text articles against inclusion criteria.

Data Extraction

The primary outcome was the reported size of a singular nodule or the largest thyroid nodule (if multiple present) reported on initial thyroid ultrasonography. Two investigators (Y.Z. and A.A.) extracted the following data: study characteristics (country, publication year, study period), patient characteristics (sample size, age, sex), nodule size (maximum diameter, mean/median with distribution), and ultrasonography and technique characteristics (ultrasonography manufacturer, model, frequency, probe, and specialty of the clinician performing the ultrasonography). Discrepancies between reviewers were resolved by consensus, then by a senior investigator (D.O.F.) if consensus could not be reached.

Risk of Bias Assessment

Two investigators (Y.Z. and A.A.) independently conducted a risk of bias (ROB) assessment of each study with an adapted ROBINS-I (Risk Of Bias In Non-Randomized Studies of Interventions) tool. This tool is commonly used in systematic reviews of nonrandomized intervention studies.¹³ Selection bias and bias due to missing data domains were scored using the following scheme: low (0 points), moderate (1 point), serious (2 points), or critical ROB (3 points). Studies with overall scores of 0 to 1 points were considered low risk, 2 points moderate risk, and greater than 3 points high ROB. Studies with high ROB were excluded from the analysis. Discrepancies between reviewers were resolved by consensus; if a consensus was unable to be reached, the discrepancy was settled by a senior investigator (D.O.F.). The robvis package of R (version 0.3.0; R Foundation) was used for the presentation of ROB results.¹⁴

Data Synthesis and Meta-Analysis

To ascertain the association between calendar year and mean thyroid nodule size reported via ultrasonography, we defined the analysis year of each study as the median between the start and end year of data collection reported by each included study. If this was not available, we instead calculated the mean offset between the publication year and analysis year of the other studies and subtracted this from study publication year.¹⁵

We used the mean nodule size from each study to model the temporal trend. The mean was used when possible and otherwise imputed by adding the average mean-median difference to the median across studies for which both were reported. If standard error (SE) was not reported, it was estimated by dividing the mean SD by the square root of the sample size.¹⁵ If SD was not reported, it was imputed using the mean SD across all studies that reported SD. The mean (SD) age were computed similarly.

A mixed-effects meta-regression model estimating mean nodule size as a function of the elapsed number of years between 1990 and the analysis year of each study was performed, controlling for mean patient age, the proportion of female patients, and ultrasonography indication (diagnostic or screening). The year 1990 was used because it was the first year of the analysis. Each study was weighted by SEs. We performed 2 subgroup analyses: (1) studies that performed ultrasonography for randomly screened patients (screening subgroup), controlling for years elapsed and (2) studies that consisted of patients seeking care for diagnosis of thyroid-related signs or symptoms (diagnostic subgroup), controlling for years elapsed, mean age, and the proportion of female patients.

Data analysis was conducted using the R programming language (R Foundation for Statistical Computing) and Review Manager (RevMan; Cochrane Collaboration; version 5.4.1).^16,17 The mada (version 0.5.10) and meta (version 5.2) R packages were used for meta-analysis and figure production. Subgroup analyses were performed using the exact binomial distribution (instead of the normal distribution implemented by mada) to model within-study variance.^18,19

Results

Study Characteristics

In all, 1097 studies were identified, and 1093 abstracts were screened after duplicate removal. Of these, 395 full-text articles were assessed, and 18 studies met inclusion criteria (Figure 1).^{20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37} Characteristics of included studies are listed in Table 1. Data collection years ranged from 1990 to 2021 across 9 countries. In all, these studies included 11 963 patients who underwent a first thyroid ultrasonography. The mean (SD) age of patients was 47.6 (5.2) years. The proportion of females across studies ranged from 63% to 100%. All of the patients included in the studies received care at an academic institution; there were no studies conducted at nonacademic facilities that met criteria. Ultrasonography frequency did not increase over time (median, 9 MHz; IQR, 7.8-10.9).

Figure 1. Flow Diagram of Study Inclusion in Meta-Analysis.

Table 1. Characteristics of 18 Included Studies.

Source	Country	Years of data collection	Sample size, No.	Study population screened or seeking care	Female, %	Age, mean (SD), y	Nodule size, mean (SD), mm	Ultrasonography manufacturer and model	Ultrasonography probe used	Ultrasonography frequencies used, MhZ	Ultrasonography operator and experience
Al-Chalabi et al, 201920	UK	2015	964	Seeking care	82	Median (IQR), 55 (36-75)	Median (IQR), 13 (7-46.5)	Not reported	Not reported	Not reported	Radiologists
Chung et al, 200121	South Korea	1997-1998	353	Screened	85.5	50.5	10	Advanced Technology Laboratories HDI 3000	Not reported	Not reported	1 Experienced radiologist
Clark et al, 199522a	US	1989-1992	115	Seeking care	90.4	35	Not reported	Acuson 128	Color Doppler and low-flow sensitivity	7.5	Not reported
Ferrari et al, 200823a	Italy	2006-2007	23	Seeking care	78.2	44	Not reported	Hitachi EUB 8500 Logos	Not reported	13	Not reported
Jin et al, 201924a	China	2017-2018	316	Seeking care	69.9	Men: 41.8 (12.5); women: 42.6 (13.3)	Total mean size not reported (benign vs malignant only)	Toshiba Aplio 500 Platinum	Linear phased array transducer	7-14	Not reported
Kim et al, 200825	South Korea	2005-2006	500	Seeking care	83.2	49.2	16.4 (11.3)	Philips IU-22	Not reported	10	Experienced radiologists
Kim et al, 201326	South Korea	2008-2009	1127	Seeking care	85.4	49.1	12	Philips IU-22	Linear probe	5-12	Experienced radiologist
Koike et al, 200127a	Japan	1999	309	Seeking care	90.3	53 (14)	Not reported	GE Logiq TM500MD	LA-39 linear probe	6-13	Surgeons, endocrinologists
Lee et al, 200328	South Korea	2003	697	Screened	100	42.7	8	Advanced Technology Laboratories HDI 5000	Not reported	5-12	1 Surgeon
Moifo et al, 201729a	Cameroon	2015-2015	126	Screened	65.9	42	Not reported	Hitachi Prosound alpha 6 and Sonoscape SSI-8000	Linear probe	4-11	2 Radiologists with at least 5 y experience in thyroid ultrasonography
Moon et al, 200730	South Korea	2004-2006	153	Seeking care	63	44.5 (21.3)	16.8 (11.3)	Siemens SONOLINE Antares	High-frequency linear transducer	7.5-15	2 Thyroid radiologists
Nam-Goong et al, 200431	South Korea	2000-2001	267	Seeking care	78.3	51	9 (3)	Advanced Technology Laboratories HDI 5000	Not reported	7-15	Radiologists
Parket al, 200732	South Korea	2001-2004	518	Screened	100	49 (12.3)	9.9	Advanced Technology Laboratories HDI 5000 or HDI 3000	Not reported	10-12	3 Radiologists with at least 6 y experience with breast and thyroid ultrasonography
Shayganfar et al, 202033	Iran	2018-2019	239	Seeking care	85.8	47.36 (11.9)	21.2	Philips Clearvue 650	Transducer and color Doppler mode		Expert radiologist and last-year radiology resident
Symonds et al, 201834	Canada	2021	1339	Seeking care	85	56 (15)	17.6 (1.39)	Not reported	Not reported	Not reported	34 Consultant radiologists with subspecialty training in diagnostic imaging
Tan et al, 199535a	US	1990-1991	151	Seeking care	74.8	Not reported	Not reported	Acusón 127	Not reported	5-7	Not reported
Yooet al, 201836	US	2012	1845	Screened	65.4	48.7	6.7 (5.9)	GE LOGIQ 7 and LOGIQ E9	Not reported	5-12	2 Board-certified radiologists
Zhang et al, 201537	China	2011-2013	2921	Seeking care	67.4	51.6 (11.6)	15.7 (11)	Siemens Medical Solutions S2000	Not reported	4-9	2 Board-certified radiologists

^a Not used in meta-analysis because the mean/median nodule size was not reported.

Risk of Bias

ROB results for each study are presented as a summary chart and detailed traffic light diagram (Figure 2). Five studies provided insufficient data for assessment; thus, ROB was unclear.^{26,27,28,31,32} The 13 remaining studies had a low ROB based on the criteria and were included in the analysis.

Figure 2. Risk of Bias Analysis.

D1 indicates bias due to selection of participants; D2, bias due to missing data.

Meta-Analysis

All articles that reported a central tendency for nodule size (ie, mean, median; 12 of 13 with low ROB) were meta-analyzed. The overall mean nodule size reported via ultrasonography increased by 0.52 mm each year from 1990 to 2021 (slope, 0.52; 95% CI, 0.23-0.81), adjusting for covariates (Figure 3A). Results varied in subgroup analyses. Meta-analysis of the mean nodule size reported among diagnostic studies (n = 8 studies; n = 7510 patients) showed a 0.57-mm increase annually from 2000 to 2021 (slope, 0.57; 95% CI, 0.21-0.93), adjusting for covariates (Figure 3B). Meta-analysis of the screening studies (n = 4 studies; n = 3413 patients) showed the opposite association, with mean nodule size reported via ultrasonography decreasing by 0.23 mm each year from 1990 to 2012 (slope, −0.23; 95% CI, 0.40 to −0.07), adjusting for years elapsed (Figure 3C). The associations between mean nodule size over time and other covariates are shown in Table 2.

Figure 3. Mean Nodule Size.

Studies were arranged in increasing order of analytic year. Each square represents the mean thyroid nodule size (reported or imputed) for each study. Bars represent the SD (reported or imputed) of nodule size. Studies whose mean nodule size was reported as not applicable (NA) reported neither the mean nor median size of nodules detected by ultrasonography.

^aMean nodule imputed as follows: imputed mean = median + (mean difference between mean and median across studies reporting both).

^bSD of nodule size imputed as follows: imputed SD = mean SD across studies reporting SD.

Table 2. Meta-Regression Covariates With Slope Estimates by Analysis Group.

Variable	Slope (95% CI)
All studies
Years elapsed	0.52 (0.23 to 0.81)
Mean age	0.08 (−0.46 to 0.61)
Percentage female	0.18 (0.03 to 0.33)
Screening (asymptomatic)	−6.12 (−10.08 to −2.15)
Diagnostic subgroup
Years elapsed	0.57 (0.21 to 0.93)
Mean age	−0.02 (−0.74 to 0.70)
Percentage female	0.07 (−0.26 to 0.41)
Screening subgroup
Years elapsed	−0.23 (−0.40 to −0.07)

Discussion

The size of thyroid nodules reported via ultrasonography changed over time. Three specific trends were noted: (1) overall nodule size reported via ultrasonography increased by 0.52 mm per year; (2) reported nodule size increased by 0.57 mm per year from 1990 to 2021 in patients undergoing ultrasonography for diagnostic purposes; and (3) reported nodule size decreased by 0.23 mm per year from 1990 to 2012 in randomly screened populations. Based on our metaregression, the reported nodule size increased by a mean of 15 mm in the 3 decades since 1990. Altogether, these findings affirm the shifting attitude regarding the clinical importance of small nodules and how nodules are risk stratified and reported.

Increase in Diagnostic Nodule Size Over Time

The increase in reported nodule size over time is likely the byproduct of introduction, adoption, and/or changes in nodule risk stratification systems, clinical guidelines, and radiology practice patterns that were implemented in response to concerns regarding overdetection of subclinical nodules.^4,7,8,38 Thyroid nodule guidelines have evolved to improve the diagnostic yield of biopsies and in recognition of the growing body of evidence that thyroid nodules are overdetected, with consequent misdirected use of valuable health care resources.^4,8,9 The ATA published nodule guidelines in 2006, 2009, and 2015, with each iteration providing increased guidance on nodule size and characteristics that should prompt biopsy.^4,39,40 These evolving guidelines have put increased importance on suspicious ultrasonography characteristics and now only recommend biopsy of nodules less than 1 cm if they have intermediate or high likelihood of cancer based on suspicious ultrasonography features. Biopsy is not recommended for nodules with very low likelihood of cancer until they are 2.0 cm or larger.

In addition to the ATA guidelines, the ACR TI-RADS was published in 2017 to provide guidance on how to risk stratify thyroid nodules seen on ultrasonography. This standardized scoring system assigns points for suspicious features, such as solid composition, hypoechogenicity, taller than wide shape, irregular margin, and calcifications. The total number of points determines the category (1-5), with higher levels being more suspicious for cancer.⁷ This classification is used in conjunction with size criteria to determine the need for and timing of biopsy or follow-up. ACR TI-RADS only recommends follow-up for moderately suspicious nodules if they are 1.0 cm or larger and biopsy if they are 1.5 cm or larger. Even for highly suspicious nodules, it recommends follow-up for nodules 0.5 cm or larger and biopsy only if the nodule is 1 cm or larger. Many international versions of TIRADS-like risk stratification systems exist (eg, European Thyroid Association TIRADS and the Korean Society of Thyroid Radiology/Korean Thyroid Association TIRADS), and all use suspicious features in conjunction with nodule size to guide reporting and biopsy thresholds.⁴¹

The ATA guidelines and other risk stratification systems provide guidance that is intended to improve the diagnostic yield of biopsies and recommend reporting only on nodules that appear clinically relevant. These changes are based on growing evidence that subcentimeter nodules should only be reported if they have specific abnormal ultrasonographic features. Before recognizing the importance of suspicious ultrasonography features, reporting guidance was lacking, which led to widely divergent reporting behaviors associated with small and subcentimeter nodules. It is highly likely that improved awareness and adherence to guidelines and risk stratification systems in clinical practice explains the increasing size of reported nodules over time in this analysis.

Independent of improved guidelines, attitudes in radiology have shifted to reflect efforts to mitigate overdetection of subclinical disease and reduce unnecessary biopsies.^42,43 The behavior of radiologists in reporting of thyroid nodules has been shown to vary substantially in documentation of features based on their own preferences and experience.^42,43 For example, Hoang et al⁴³ demonstrated that surveyed radiologists agreed only 53% of the time on when to report incidental thyroid nodules, with increased disagreement when nodules are smaller than 1 cm. There seems to be greater consensus around reporting larger nodules associated with their higher likelihood of clinical importance; therefore, they are more readily found in the findings or impression of the radiologic report. This attitude shift is supported by our data that demonstrate a growth in size of thyroid nodules reported on diagnostic ultrasonography. Over time, interpretation of diagnostic ultrasonography seems to have become increasingly regimented and more aligned with guideline recommendations, which do not advocate reporting of small nodules that do not exhibit suspicious sonographic characteristics.

Decrease in Screening Nodule Size Over Time

The opposite association was seen in thyroid nodule screening studies, in which there was a decrease in reported nodule size over time. There are 2 primary explanations for this finding. First, the goal of screening studies was to detect any nodules rather than only those that would be considered clinically important, which would include nodules down to less than 0.5 cm. The US Preventive Services Task Force recommends against thyroid cancer screening, specifically citing evidence from studies that detail the natural history of small thyroid nodules as slow-growing with low potential for recurrence, cancer, or mortality.⁴⁴ The US Preventive Services Task Force also cited South Korea’s screening protocol, a program that was associated with an increase in the population’s thyroid cancer diagnosis rate from 5 cases per 100 000 persons in 1993 to 70 cases per 100 000 persons in 2011.^44,45 The increase in diagnosed thyroid cancer occurred without an associated increase in disease-specific mortality and was used as evidence against a screening protocol recommendation.⁴⁵ Our data showed that nodules reported in screened populations were small and decreased in size over time, indicating low diagnostic and clinical importance. Subcentimeter nodules are prevalent in asymptomatic individuals, and their identification may be associated with more harm than benefit.

A second reason for the decreasing size of nodules in screening studies is associated with patient selection. Selected patients included in the screening studies did not have an indication for undergoing diagnostic ultrasonography. For example, they had no known incidental nodule(s) noted on unrelated cross-sectional imaging and no thyroid-attributable symptoms. This contrasted with patients in the diagnostic group, who necessarily had an indication to justify their first ultrasonography (eg, palpable mass, symptoms). Guidelines for diagnostic evaluation of a thyroid nodule recommend reporting nodules larger than 1 cm or smaller than 1 cm with suspicious findings.^4,8,42,43 The screening studies in this analysis were conducted before the adoption of most guidelines, so they included small, insubstantial nodules that would not be reported today, likely accounting for the opposing findings between diagnostic and screening studies.

Clinical Implications

The results highlight the shifting landscape in thyroid nodule workup. The screening subgroup findings support recommendations against thyroid cancer screening, given that indolent, subclinical nodules are common in the general population, and, on a population level, their discovery could do more harm than good.⁴⁶ The increasing overall size of reported nodules in the diagnostic population demonstrates that the medical community has been responsive to practice guidelines and risk stratification systems that promote appropriate care by more accurately identifying nodules that represent clinically relevant disease.

Limitations

The observational studies that were analyzed are susceptible to selection bias, as the patients included were not randomly selected. Second, there was a limited number of studies involved in the screening subgroup analysis (n = 4), and we can only comment on nodule size reported up to 2012, when the last screening study was published. The discrepancy in number of patients analyzed in this subgroup compared with the diagnostic subgroup was also significant; therefore, the overall nodule size increase was weighted more toward the diagnostic group. Third, factors associated with ultrasonography technology and interpretation were inconsistently reported across studies. Fourth, all studies meeting inclusion criteria were performed at academic institutions. Thus, our findings may not generalize to private and community practice settings where ultrasonography practice patterns may differ. Finally, studies only reported the largest nodule per patient; therefore, smaller co-occurring nodules were not represented in these data.

Conclusions

The results of this systematic review and meta-analysis suggest that size of thyroid nodules reported via ultrasonography has changed over time, increasing annually for patients undergoing diagnostic ultrasonography and decreasing for screened asymptomatic patients. Increasing size of nodules reported over time is likely due to the introduction of risk stratification systems and guidelines, as well as changes in radiology practice patterns. In contrast, the decrease in nodule size reported in asymptomatic, screened populations shows that small thyroid nodules are prevalent in the general population and can easily be detected with current technology. Ready detection of small subclinical nodules in asymptomatic patients supports the recommendation against thyroid screening. Our study provides insight into how guidelines, risk stratification systems, and changes in practice patterns may have changed how thyroid nodules have been reported over time and may inform policies associated with thyroid nodule management.

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