Sonographic evaluation of the thyroid size in neonates.

PURPOSE:To validate the use of the ratio between the total transverse diameters of the thyroid lobes (Th) and the width of the trachea (Tr)-the Th:Tr or Yasumoto ratio-as a sonographic method for estimating thyroid size, and to determine reference values for this ratio and for thyroid volume in neonates. METHODS:In this cross-sectional study, we evaluated thyroid size according to the Yasumoto ratio and the thyroid volume calculated with the ellipsoid formula in 125 healthy, euthyroid, iodine-sufficient, full-term neonates. RESULTS:The mean thyroid gland volume was 1.00 ml (95% confidence interval, 0.95-1.03 ml), and the mean Yasumoto ratio was 2.29 (95% confidence interval, 2.21-2.31). The lower- and upper-limit results falling within 2 SDs of the mean were 0.45 ml and 1.53 ml for the volume and 1.71 and 2.87 for the ratio. CONCLUSIONS:In full-term, euthyroid, iodine-sufficient neonates, the normal reference interval for thyroid volume measured on sonography was 0.45-1.53 ml and that for the Yasumoto ratio was 1.71-2.87. A ratio of 1.7 may be applied as the cutoff value for sonographic diagnosis of thyroid dysgenesis in full-term neonates with congenital hypothyroidism. © 2014 Wiley Periodicals, Inc. J Clin Ultrasound 43:224-229, 2015.