To elucidate the role of thyroid ultrasound (TU) in the diagnosis of congenital hypothyroidism (CH), we compared 1) TU and thyroid scintigraphy (TS) in 6 CH newborns and 2) TU results in the 6 CH newborns, in 8 newborns with "false positive" results at screening, in 13 CH children aged 2 mo to 12 yr treated since the neonatal period and in 235 controls aged 0-12 yr.
Results: 1) In all 6 CH newborns with no thyroid uptake at TS, TU evidenced small posterior hyperechogenic masses in the thyroid area [Vol: 322 +/- 180 (SD) mm3]; 2) In all normal controls and in the 8 "false positive" cases at screening TU showed normal thyroid structures. The thyroid volume was 831 +/- 383 mm3 in normal newborns and progressively increased with age. In the older CH children, TU also demonstrated the hyperechogenic masses, but their volume barely increased with age: as a consequence, the difference between the volume of the masses in CH patients and the thyroid tissue in controls, already significant in newborns (p less than 0.01), markedly increased with age. The exact nature of these masses is unknown; they could represent poorly vascularized ultimobranchial remnants containing the calcitonin - secreting cells: this hypothesis is supported by our finding that serum concentrations of calcitonin (measured by a sensitive extraction method) (mean +/- SD, pg/ml) were lower in the CH patients (2.9 +/- 1.5) than in controls (13.0 +/- 6.9; p less than 0.001) at birth. In conclusion, in all cases of CH, TU showed abnormal structures in the thyroid area. TU and TS provide complementary information in the diagnosis of CH, and TU should be routinely performed in all newborns suspected of CH to avoid unnecessary use of TS in unaffected infants.