Ultrasound determination of pediatric thyroid mass.

Background: Radioiodine therapy for Graves disease can be achieved with dosing based on estimated thyroid gland mass. Thyroid mass can be estimated using linear ultrasound measurements, and conversion factors for volume and density. The choice of conversion factors could impact estimated thyroid mass and thus administered radioiodine dose.

Objective: The objective of this study was to define the relationship between thyroid mass estimated by ultrasound and measured thyroid mass following thyroidectomy.

Materials And Methods: This was a retrospective, exempt study that included patients < 18 years of age with < 6 months between thyroid ultrasound and thyroidectomy January 2010-June 2020. Thyroid dimensions by ultrasound, thyroid mass at thyroidectomy and histopathological diagnosis were collected. Published conversion factors were used to estimate thyroid volume with conversion to mass using a density of 1.05 g/cm. Pearson correlations and Bland-Altman difference analyses were used to define the relationship between estimated mass and specimen weight. Linear regression was used to calculate an optimal conversion factor for estimating thyroid mass.

Results: We included 86 patients, 67 female (78%), with a mean age of 14.5 ± 3.15 years. Mass estimated using all tested conversion factors had similar strong, positive correlation with specimen weight (r = 0.95). The mean difference between thyroid mass estimated by ultrasound and measured mass ranged from - 0.34 g (conversion factor = 0.523) to 1.69 g (conversion factor = 0.554). The optimal simplified factor for estimation of thyroid mass for the study sample was 0.537.

Conclusion: All published conversion factors for estimating thyroid mass based on linear ultrasound measurements produce good estimates of thyroid mass. Errors in estimated mass are less than 2 g on average.