Growth rates of malignant and benign thyroid nodules in an ultrasound follow-up study: a retrospective cohort study

BACKGROUND: Thyroid nodules are frequently detected by cervical ultrasound examinations. In follow-up studies, malignant as well as benign nodules may exhibit an increase in size. The objective of our investigation was to test whether histologically determined malignant and benign thyroid nodules show differences in growth rates above a defined significance level. METHODS: A retrospective ultrasound cohort follow-up study from 4 to 132 months included 26 patients with differentiated carcinomas and 26 patients with adenomas of the thyroid gland. Significance levels were determined by intra- and interobserver variations of volumetric measurements in 25 individuals. RESULTS: Intra- and interobserver volumetric measurements were highly correlated (r = 0.99 and r = 0.98, respectively), with variations of 28 and 40%, respectively. The growth rates of malignant and benign nodules did not show differences with respect to two sonographic measurements (d = − 0.04, 95%CI(P): 0.41–0.85, P = 0.83). Using shorter increments and multiple measurements, growth rates of malignant nodules revealed significantly higher values (d = 0.16, 95%CI(P): 0.02–0.04, P = 0.039). CONCLUSIONS: The growth rates of benign and malignant thyroid nodules do not appear to differ using two sonographic volumetric measurements. However, due to temporal changes in cellular proliferation and arrest, malignant nodules may exhibit higher growth rates with multiple assessments and shorter increments.