Benign thyroid nodules on cytology : results of long-term follow up with ultrasonography

Abstract

Background: Repeated fine needle aspiration (FNA) is generally recommended for cytologically confirmed benign thyroid nodules demonstrating growth on follow-up ultrasonography (US). However, little is known about the natural history of cytologically confirmed benign thyroid nodules. This study investigated the natural history of FNA-confirmed benign thyroid nodules on US and to determine growth predictors for volume increases greater than 50%. Methods: This retrospective observational cohort study enrolled 854 FNA-confirmed benign thyroid nodules from 819 patients with at least one more follow-up US since the initial US-guided FNA. Nodule volumes were measured at each US and the growth criteria was defined as an increase in volume of 50% or greater. Changes of nodule size were correlated with demographic and US characteristics of each nodule. Incidence of malignancy was investigated. Results: The majority of (79.7%) benign thyroid nodules did not change in size or decreased with the defined growth criteria during 47 months of mean follow up time (range: 7-101months). The estimated proportion with growth greater than 50% in volume was 8.1% at 4 years and 62.2% at 8 years. More than 4 years of follow up time, younger age and less than 25% of cystic component were independent growth predictors. Ten malignant nodules were detected, and eight out of them were stable in size during the follow up time but had suspicious US features. Conclusion: FNA-confirmed benign thyroid nodules do grow slowly over the long-term follow up time of more than 4 years. More than 4 years of follow up time, younger age and less than 25% of cystic component were independent growth predictors for volume increases greater than 50%.