Temporal Trends in Thyroid Nodule Size on Ultrasonography: A Systematic Review and Meta-Analysis

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.

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

Figure 2.. Risk of Bias Analysis

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

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.