Original InvestigationIncidental Thyroid Nodules in the National Lung Screening Trial: Estimation of Prevalence, Malignancy Rate, and Strategy for Workup
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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Cited by (0)
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.