Risk of thyroid cancer in a lung cancer screening population of the National Lung Screening Trial according to the presence of incidental thyroid nodules detected on low-dose chest CT

Abstract

Purpose: This study evaluated thyroid cancer risk in a lung cancer screening population according to the presence of an incidental thyroid nodule (ITN) detected on low-dose chest computed tomography (LDCT).

Methods: Of 47,837 subjects who underwent LDCT, a lung cancer screening population according to the National Lung Screening Trial results was retrospectively enrolled. The prevalence of ITN on LDCT was calculated, and the ultrasonography (US)/fine-needle aspiration (FNA)-based risk of thyroid cancer according to the presence of ITN on LDCT was compared using the Fisher exact or Student t-test as appropriate.

Results: Of the 2,329 subjects (female:male=44:2,285; mean age, 60.9±4.9 years), the prevalence of ITN on LDCT was 4.8% (111/2,329). The incidence of thyroid cancer was 0.8% (18/2,329, papillary thyroid microcarcinomas [PTMCs]) and was higher in the ITN-positive group than in the ITN-negative group (3.6% [4/111] vs. 0.6% [14/2,218], P=0.009). Among the 2,011 subjects who underwent both LDCT and thyroid US, all risks were higher (P<0.001) in the ITNpositive group than in the ITN-negative group: presence of thyroid nodule on US, 94.1% (95/101) vs. 48.6% (928/1,910); recommendation of FNA according to the American Thyroid Association guideline and Korean Thyroid Imaging Reporting and Data System guideline, 41.2% (42/101) vs. 2.4% (46/1,910) and 39.6% (40/101) vs. 1.9% (37/1,910), respectively.

Conclusion: Despite a higher risk of thyroid cancer in the LDCT ITN-positive group than in the ITN-negative group in a lung cancer screening population, all cancers were PTMCs. A heavy smoking history may not necessitate thorough screening US for thyroid incidentalomas.

Keywords: Incidental thyroid nodule; Low-dose chest CT; National Lung Screening Trial; Thyroid neoplasms; Ultrasound.

Fig. 1.. Flowchart of patient enrollment.

LDCT, low-dose chest computed tomography; ITN, incidental thyroid nodule; US, ultrasonography; FNA, fine-needle aspiration.

Fig. 2.. Types of incidental thyroid nodule calcification (arrows) on low-dose chest computed tomography: punctate (A), rim (B), and coarse (C).

Fig. 3.. A 71-year-old man (34 packyear smoking history) with an incidental thyroid nodule on lowdose chest computed tomography (LDCT) that was proven to be a benign follicular nodule.

A. LDCT shows a 2.0-cm low-attenuating nodule (arrows) in the left hemithyroid. B. Ultrasonography reveals a 1.8-cm, slightly hypoechoic, well-defined, ovoid solid nodule in the left hemithyroid. It was reported to be a benign follicular nodule (Bethesda category 2) based on fine-needle aspiration results.

Fig. 4.. A 60-year-old man (180 pack-year smoking history) with an incidental thyroid nodule (arrows) on low-dose chest computed tomography (LDCT), which was proven to be a papillary thyroid microcarcinoma.

A. LDCT shows an 11-mm low-attenuating nodule in the left hemithyroid. B. Ultrasonography reveals a 13-mm, heterogeneous, ovoid solid nodule (arrows) in the left hemithyroid. It was suspected to be a papillary thyroid carcinoma (Bethesda category 5) based on fine-needle aspiration results. Surgery confirmed the 9-mm papillary thyroid microcarcinoma without extrathyroidal extension.

Fig. 5.. A 61-year-old man (37 pack-year smoking history) with an incidental thyroid nodule on low-dose chest computed tomography (LDCT), which was proven to be nodular hyperplasia and concurrent papillary thyroid carcinoma.

A. LDCT shows a 33-mm low-attenuating nodule with punctate calcifications (arrows) in the left hemithyroid. B. Ultrasonography reveals a 26-mm ill-defined, isoechoic, predominantly solid nodule (arrows) in the left hemithyroid, which was finally proven to be nodular hyperplasia. C. Unexpectedly, ultrasonography showed another 8-mm low-echoic, suspicious nodule with spiculated margin (arrows) in the left hemithyroid, which was finally confirmed to be a 5-mm papillary thyroid microcarcinoma without extrathyroidal extension during surgery.