Elsevier

Academic Radiology

Volume 25, Issue 9, September 2018, Pages 1152-1155
Academic Radiology

Original Investigation
Incidental Thyroid Nodules in the National Lung Screening Trial: Estimation of Prevalence, Malignancy Rate, and Strategy for Workup

https://doi.org/10.1016/j.acra.2018.02.016Get rights and content

Rationale and Objectives

There is limited research on the prevalence of incidental thyroid nodules (ITNs) in the United States screening population and on the appropriate evaluation of computed tomography (CT)-detected ITNs. The purpose of this study is to determine the prevalence of ITNs in the National Lung Screening Trial (NLST) and develop a workup strategy for ITNs.

Materials and Methods

CT images were obtained for subjects with documented thyroid abnormalities in the CT screening arm of the NLST, subjects diagnosed with thyroid malignancies, and control subjects. Several size thresholds were compared to determine how many nodules would be further evaluated and how many thyroid malignancies would be missed had each threshold been applied at the time of workup.

Results

Thyroid nodules were reported in 0.7% (117 of 17,309 subjects). In 663 control subjects without reported thyroid nodules, thyroid nodules were identified in 78 (11.8%). Reported nodules were larger than unreported nodules (21.3 vs 16.9 mm, P = .03). Thyroid malignancies were diagnosed in 0.1% (22 of 17,309). If a 20-mm rather than a 10-mm cutoff were used to determine which nodules should be further evaluated, all malignancies would be detected, but 24 rather than 62 patients would require workup, for a workup reduction rate of 48.7% (38 of 78).

Conclusions

Less than 1% of subjects in the NLST had reported ITNs. The true prevalence of ITNs was estimated to be 11.8%, which provides a better approximation of the number of patients who could potentially receive workup. A 20-mm rather than a 10-mm cutoff would reduce the workup rate by almost 50% while still capturing all malignancies.

Introduction

A commonly encountered incidental finding on chest computed tomography (CT) examinations is the incidental thyroid nodule (ITN) 1, 2. The majority of imaging-detected ITNs are benign, but the possibility of malignancy can prompt further evaluation with ultrasound and fine needle aspiration biopsy (FNAB) 3, 4. If the FNAB results are not conclusive, additional tests and interventions may ensue, including ultrasound surveillance, repeat FNAB, and even surgery for histopathologic diagnosis (5).

There are currently no studies on the prevalence of ITNs in the United States lung screening population. Several European and Canadian CT lung screening trials, the largest of which had 5200 trial participants, found that ITNs are reported in less than 5% of patients 6, 7, 8, 9. Furthermore, there is limited research on the appropriate workup and management of ITNs identified on CT, which has led to variable reporting practices among radiologists 10, 11.

This study involves review and analysis of data from the CT screening arm of the National Lung Screening Trial (NLST) (12). The purpose is to determine the prevalence of ITNs on CT in the screening population of the NLST, to determine the incidence of thyroid malignancy, and to compare several size thresholds for CT-detected ITNs.

Section snippets

Study Population

Anonymized data were obtained from the NLST, which was a randomized controlled trial of screening tests for lung cancer (12). From 2002 to 2004, more than 53,000 participants aged 55–74 years, with a history of heavy smoking but no lung cancer, were randomly assigned to two study arms in equal proportions (low-dose spiral CT or chest radiography). Of the 26,722 subjects randomized to the CT screening arm of the NLST, the Lung Screening Study randomized 17,309 (64.8%) through 10 screening

Results

There were 17,309 subjects (mean age 61.3 years, standard deviation [SD] 5.0 years) who underwent CT in the Lung Screening Study. Of these subjects, 10,568 (61.1%) were male, and 6741 (38.9%) were female. Thyroid abnormalities were reported by NLST readers in 221 subjects (thyroid nodules in 117, thyroid gland enlargement or goiter in 101, thyroidectomy in 2, and thyroid atrophy in 1). Thus, thyroid nodules were reported by NLST readers in only 0.7% (117 of 17,309 subjects). The reported

Discussion

This study finds that the proportion of subjects with reported ITNs in the CT screening arm of the NLST was less than 1%. The true prevalence of ITNs in the lung cancer screening population was found to be approximately 11.8%. There were few thyroid malignancies (22 total) diagnosed during the study period of the NLST. Assuming that imaging-detected thyroid nodules led to the diagnosis of malignancy during the study period, the data suggest that a 20-mm rather than a 10-mm cutoff to determine

Acknowledgments

This project was funded by the 2014-15 American Society of Head and Neck Radiology William N. Hanafee Research Grant. The author thanks the National Cancer Institute for access to its data collected by the NLST. The author also thanks Ken Clark, Joshua Rathmell, Tom Riley, and Brett Thomas for providing the datasets and CT images.

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This project was funded by the 2014-2015 American Society of Head and Neck Radiology (ASHNR) William N. Hanafee Research Grant and was presented at the ASHNR Annual Meeting in September 2015.

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