What can the National Lung Screening Trial teach us about incidental thyroid nodules?

How common are incidental thyroid nodules (ITNs) in the U.S. screening population? And which ITNs should receive further evaluation? A researcher from Duke University Medical Center in Durham, North Carolina, examined data from the National Lung Screening Trial (NLST) to answer those questions, sharing her findings in a new study for Academic Radiology.

Manisha Bahl, MD, MPH, studied data from more than 17,000 patients from the CT screening arm of the NLST. All patients were between the ages of 55 and 74 “with a history of heavy smoking but no lung cancer.” Overall, ITNs were reported in just 0.7 percent of those patients. This lines up with prior U.S. lung screening trials that found ITNs in less than 5 percent of patients. 

“These percentages are less than expected; however, in a clinical trial setting, readers are advised to record findings only if the findings are considered significant,” Bahl wrote. “Outside of a clinical trial, radiologists report findings less judiciously. The true prevalence of ITNs in the lung cancer screening population was found to be approximately 11.8 percent, which provides a better estimation of the number of patients who could potentially receive workup when reported by radiologists outside of the clinical trial setting.”

A total of 22 thyroid malignancies were diagnosed during the NLST study period. The NLST’s 10-mm cutoff for determining which ITNs require further evaluation could potentially be changed, Bahl explained, while still providing the same level of high-quality care to patients who need it.

“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 which nodules require further evaluation would reduce the workup rate by almost 50 percent while still capturing all malignancies,” Bahl wrote.

Bahl added that the study did have limitations, including the fact that NLST results “may not be generalizable to other populations.” Also, the CT exams were performed as part of a lung cancer screening trial, so the entire thyroid gland may have not been in the field of view for every exam.