DISCREPANCY BETWEEN THE RESULTS OF THYROID ECHOCRAPHY (TE) AND THYROID SCINTICRAPHY (TS) IN CONCENTAL HYPOTHYROIDISM (CH)

Abstract

It has been proposed that TE could replace TS in the detection of thyroid tissue for the diagnosis of CH suspected by neonatal screening. However, only limited experience is presently available on TE in normal and CH infants. Therefore 1) we determined the echographic characteristics of the thyroid gland in normal newborns; 2) we compared the results obtained by TS and TE in GH infants. We studied 48 normal newborns aged 5±3 days, and 9 infants with CH detected in the neonatal period and aged respectively 11, 14, 18, 19 days, 3, 4 months and 1, 8, 9 years. TE was performed in all infants but TS only in the CH infants. Results : 1) Normals: the mean (± SD) thyroid volume (V of one lobe : length × Breadth × Deepth × 17/6)was 801±354 mm3. As compared to the neck musculature, the thyroid appeared hypo-(13 %), slightly hyper-(79 %) or strongly hyperechogenic (8 %). 2) CH infants : 99mTc TS displayed no uptake in 4 cases (agenesis) and a low uptake at the base of the tong in 5 cases (ectopia). In contrast, TE unquestionably revealed in all cases a small, bilobate and strongly hyperechogenic tissue located in the normal position of the thyroid with a mean volume of 512±95, irrespectively of age and sex. Conclusion : in 9 cases of CH with thyroid agenesis or ectopia, TE systematically detected structures in the normal position of the thyroid, though different in size and echogenicity as compared to the normal gland. Th is tissue could represent the ultimobranchial bodies. Therefore, TE cannot replace TS for the diagnosis of CH.

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