Thyroid Nodule Growth as A Predictor of Malignancy

Abstract

Objective: To assess which measure of thyroid nodule growth on serial neck ultrasound, if any, is associated with malignancy. Methods: Retrospective exploratory chart review of malignant thyroid nodules assessed at Kingston Health Sciences Centre (2006-2016) and benign thyroid nodules (2016), at least 1 cm in diameter and with 2 ultrasounds completed at least 30 days apart. Groups were compared using independent samples Student's t test, chi-square test, or Mann-Whitney U test as appropriate, as well as multivariable logistic and linear regression modelling to adjust for age and baseline volume. Results: One hundred and seventy-eight nodules were included in the study. When growth was defined as >20% increase in 2 dimensions (minimum 2 mm), malignant nodules (MNs) underwent significantly more growth than benign nodules (BNs) (16.8% BN versus 29.8% MN [P = .026]; odds ratio = 2.49; 95% confidence interval = 1.12 to 5.56). There was no significant difference between the groups when growth was defined as >2 mm/year or ≥50% volume growth. Nodules shrank >2 mm/year in each group and the difference was not statistically significant (24.2% BN versus 20.7% MN [P = .449]). The median doubling time for the nodules that grew was 1022.1 days in the BN group and 463.2 days in the MN group (P = .036). The median doubling time for all nodules was 456.5 days in the BN group and 244.2 days in the MN group (P = .015). Conclusion: Thyroid nodule growth defined as >20% increase in 2 dimensions (minimum 2 mm) is associated with risk of malignancy. Nodule shrinkage did not distinguish between BNs and MNs. Abbreviations: BN = benign nodule; CI = confidence interval; FNA = fine needle aspiration; KHSC = Kingston Health Science Centre; MN = malignant nodule; OR = odds ratio; ROC = receiver operating characteristic.