Correlation between the size of incidental thyroid nodules detected on CT, MRI or PET-CT and subsequent ultrasound

PurposeThe aim of this study was to assess the relationship between size of thyroid nodules at computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography CT (PET-CT), and size at ultrasound.Materials and methodsWe performed a retrospective review of thyroid ultrasound studies over a 2-year period.ResultsA total of 307 patients were included in the study. There was a statistically significant difference between the size of nodules measured on ultrasound compared with cross-sectional imaging (P < .001). American College of Radiology white paper recommendations would have decreased ultrasound referrals by 24% without any additional missed malignancies.ConclusionCross-sectional imaging underestimates the size of thyroid nodules; however, the difference is small and likely not clinically significant.